A new technical paper titled “Calibration and Performance Evaluation of a Superconducting Quantum Processor in an HPC Center” was published by researchers at Leibniz Supercomputing Centre, IQM Quantum Computers, and Technical University of Munich.

Abstract

“As quantum computers mature, they migrate from laboratory environments to HPC centers. This movement enables large-scale deployments, greater access to the technology, and deep integration into HPC in the form of quantum acceleration. In laboratory environments, specialists directly control the systems’ environments and operations at any time with hands-on access, while HPC centers require remote and autonomous operations with minimal physical contact. The requirement for automation of the calibration process needed by all current quantum systems relies on maximizing their coherence times and fidelities and, with that, their best performance. It is, therefore, of great significance to establish a standardized and automatic calibration process alongside unified evaluation standards for quantum computing performance to evaluate the success of the calibration and operation of the system. In this work, we characterize our in-house superconducting quantum computer, establish an automatic calibration process, and evaluate its performance through quantum volume and an application-specific algorithm. We also analyze readout errors and improve the readout fidelity, leaning on error mitigation.”

Find the technical paper here. Published May 2024.

X. Deng, S. Pogorzalek, F. Vigneau, P. Yang, M. Schulz and L. Schulz, “Calibration and Performance Evaluation of a Superconducting Quantum Processor in an HPC Center,” ISC High Performance 2024 Research Paper Proceedings (39th International Conference), Hamburg, Germany, 2024, pp. 1-9, doi: 10.23919/ISC.2024.10528924.

The post Characterizing and Evaluating A Quantum Processor Unit In A HPC Center appeared first on Semiconductor Engineering.

The semiconductor industry is preparing for the migration from proprietary chiplet-based systems to a more open chiplet ecosystem, in which chiplets fabricated by different companies of various technologies and device nodes can be integrated in a single package with acceptable yield.

To make this work as expected, the chip industry will have to solve a variety of well-documented technical and business issues, and it will have to rein in some of the grander visions of what’s possible — at least initially. The basic challenge is aligning domain-specific performance demands of end systems, which contain a growing number of chiplets, with the assembly and packaging capabilities and methodologies of IDMs, foundries, and OSATs. This includes the creation of assembly development kits (ADKs) that are roughly the equivalent of process development kits (PDKs), which today are codified with manufacturing specifications.

A PDK provides the appropriate level of detail needed to develop planar chips, marrying design tools with fab processes to achieve a predictable outcome. But making this work for an ADK with heterogeneous chiplets is many times more complex. Design and assembly teams need to manage thermal, mechanical, and electrical co-dependencies that cause electrical and mechanical stress, resulting in warpage, reduced yield, and reliability issues under real-world workloads. Layered on top of this the business and legal issues related to packaging of different devices from different manufacturers.

“Chiplets are a growing trend, especially in the HPC and networking segments, with potential to scale to other applications,” said Gabriela Pereira, technology and market analyst for semiconductor packaging at Yole Intelligence. “The industry has understood that high-end advanced packaging technologies are needed to connect them — but that’s much more complex than it seems. Connecting chiplets requires the design of high-bandwidth interconnections at the package level, which can take different forms — e.g., 2D, 2.5D or 3D — while ensuring that the thermal and power requirements are fulfilled.”

Commercial chiplet-based devices generally are domain-specific, and sometimes developed for a specific workload. So despite a big industry push to create a LEGO-like mix-and-match ecosystem for chiplets — which today includes multiple IP and EDA vendors, foundries, memory suppliers, OSATs, substrate suppliers, etc. — making this work as planned will require time and a massive amount of work.

Fig. 1: System assembly requires tighter coupling between chipmakers and OSATs. Source: ASE

In creating heterogeneous integrated designs, it’s essential to have much tighter collaboration between foundries, IDMs, OSATs, and PCB manufacturers. And because each chiplet-based system will be customized, the number of assembly processes will grow substantially. For example, one OSAT noted that among its ~5,000 customers, there are ~1,000 different assembly processes.

That diversity in products and processes makes it difficult to achieve predictable results by choosing chiplets from a large menu of options.

“We’ve already encountered a lot of limitations including not only the silicon, but also integration and the ecosystem,” said Lihong Cao, senior director at ASE Group, at MEPTEC’s Road to Chiplets forum. She stressed that customers continue to push for a low-cost chiplet assembly process, which is creating constructive tension between developing a sophisticated assembly process and the economic realities of different industry sectors. Computing devices for automotive have a higher cost sensitivity than for data centers, for example, but their chips operate in a harsher environment over a longer lifetime.

What’s needed is a defined set of assembly process recipes — basically, a highly limited menu of choices — that are specific to the end application (HPC, automotive, RF telecommunications) in order to lower the cost of chiplet-based systems. OSATs and foundries already are moving in that direction for high-performance computing. For example, at its 2024 Direct Connect event, Intel shared its six different package processes for chiplets. TSMC and Samsung also offer defined sets of chiplet processes. But the success of these assembly processes requires engineering teams to co-optimize the flows, processes, and materials to best match the system requirements.

Fig. 2: Integrated platform development requires tightly coupled architectural analysis that co-optimizes the system design to architecture to assembly process and packaging material selections. Source: Applied Materials

“Previously, when we designed a system we only had to be worried about the system requirements. Once we start segregating into dies and reassembling them, we have to start looking at other things. We have to worry about putting them together while considering signal integrity between dies, reliability, thermals, etc.,” said Itai Leshniak, director of AI systems solutions at Applied Materials, at the MEPTEC forum. “If we take the case of AI-based computer vision, we can break it down layer by layer — on the hardware side, determining which computer vision processors, sensors, filters are needed to break it down into the architecture at layer. Then we begin to go through how to package all these chiplets, and then which materials to use and how to take advantage of those materials.”

Materials and assembly processes
Conceptually, design engineers will use chiplets to design a system. However, the co-design and integration is far more complicated than assembling a set of LEGO blocks, because the chiplets, interposers, and package substrates come from different design houses and manufacturing facilities. The advanced packaging technologies used to connect chiplets vary with an alphabet soup of names — FOWLP, FOPLP, CoWoS, etc., each of which poses additional design and material choices along with certain process limitations.

Fig. 3: There are a multitude of choices in multi-die packaging from the high-level layout to substrates, materials, bonding methods, and cooling materials. Source: Synopsys

Currently engineering teams determine the tradeoffs among the different packaging options to select materials, derive a process recipe, and determine design rules.

Materials are a good starting point. “Materials are very important because they enable new products and packaging technologies,” Tanja Braun, deputy group manager at the Fraunhofer Institute for Reliability and Microintegration IZM. “As you move into more advanced packaging, process is getting much more complex because you are putting more things together. In the end, it’s a combination of equipment, materials, and process development.”

There are three thermal parameters that are critical in package assembly processes — coefficients of thermal expansion (CTE), glass transition temperature (T_g), and thermal conductivity. These factors affect how a material behaves in manufacturing to packaging processes, as well as how it behaves in the field.

“Challenges for our materials include temperature limitations of different die,” said Rama Puligadda, CTO at Brewer Science. “We have to ensure that the temperatures used for bonding materials don’t exceed the thermal limitations of any of the chips that are being integrated into the package. Additionally, there may be some subsequent processes like redistribution layer (RDL) formation or molding. Our materials have to survive those processes. They have to survive the chemicals they come in contact with throughout the packaging process scheme. Mechanical stresses in the package add additional challenges for bonding materials.”

Within a stack of chiplets-on-substrate with an optional interposer, their material attributes affect the thermal-mechanical stresses between neighboring materials, as well. This directly impacts interconnect dimensional control over a large area substrate area.

“If you go work the numbers, you will find that the level of tolerance and control required is frightening,” said Dick Otte, CEO of Promex Industries. “You’re talking about controlling dimensions equivalent to the width of a grass blade over the length of a football field, so that’s roughly 1 in 100,000.”

The goal is uniform heating of the structure in reflow in order to attain the best process results and to avoid cracking. “When you’re taking it through a 250 degrees centigrade temperature change, then you need to heat up slowly so that the top doesn’t get hot before the bottom does,” said Otte.

Multi-physics to comprehend co-optimization
Multi-physics modeling has become the go-to method for co-optimizing packaging design and assembly process development. That affects both permanent and temporary materials, as well the placement of processors, memories, and other components.

“You always looking to what the customer needs electrically, because that’s going to help define the material set. The material set is broadly applicable to a bunch of speed ranges. As long as you don’t step outside of those electrical specifications, theoretically you should be okay,” said Mike Kelly, vice president of advanced package and technology integration at Amkor Technology.

To save many iterations of empirically based development, engineers can use physics-based simulations to understand the impact of a material set’s properties impact on the assembly process, power/thermals, and mechanical vibrations.

Consider that HPC chiplet products can consume ~1,000 watts at peak performance so the power and thermal interactions need to be fully understood.

“We’ve struggled, as everybody has, with this blizzard of complexity in the different techniques. Not only do they vary across different vendors, but they’re also varying over time,” said Marc Swinnen, director of product marketing at Ansys. “Our approach has been to identify the essentials that need to be worked on. We work jointly with customers to develop a simulation flow that actually achieves what is needed now.”

Materials are just one piece of the puzzle. “Then there’s the assembly stresses that need to be modeled to know whether you can correctly assemble this device. The third one is mechanical vibration,” Swinnen said. “Can your device withstand those regular vibrations? Modeling these attributes ties directly into our mechanical analysis tools — acoustic, thermal, vibration, etc. In the end, you’re going to have to do physics simulation. We’re trying to make it accessible to people in many different forms. But the bedrock of our tool offerings is that we have the meshing simulation and analysis. It’s a question of getting the data in the right format in a way that’s practical and usable.”

Evolving assembly design kits
For conventional packages, OSATs provide design rules for each packaging technology. These need to consider electrical, mechanical and thermal design requirements and manufacturing process limitations. In effect this is a multi-dimensional bounding box. Suppliers perform iterations with the customer to create a product specific process recipe.

Rules cover the macro-level attributes. “At a minimum, what you see from design rules is maximum package size, maximum silicon size, and whether silicon can be [mounted] on both sides of the substrate, such that when you follow these constructions the final product will have a lifetime of 1,000 thermal cycles, for example,” said Fraunhofer’s Braun.

In addition, design rules need to describe routing constraints for the interposer and/or redistribution layer, such as RDL line widths and spaces, ball-grid/pillar/pad size and pitches, and the maximum number of interconnections.

Breaking up a monolithic HPC device into multiple dies shifts some of the semiconductor design/process complexity into the packaging space. That makes things much more complicated. Consider that to connect 10 dies requires on order of 100,000 traces within the interposer’s or substrate’s redistribution layer.

To cope with the complexity at the chip level, the IC industry has long relied upon process design kits (PDKs) to capture design rules in an electronic file that can be imported into EDA tools. Their counterparts, assembly design kits (ADKs), are relatively immature.

“We call it Smart Package,” said Amkor’s Kelly. “It’s an ADK that we give to every customer who’s doing their own design. It is a set of macros, and a customization of a database tailored to a customer’s particular design. For chiplets, it is a high-density fan-out package technology. And it’s cognizant of the limitations for metal density and metal spacing, etc. This makes it easier for us to do design rule checks (DRCs).”

But right now, with the level of customization still required, how an ADK is derived and what it entails is in flux. Partnerships between EDA tool vendors, OSATs, and semiconductor device providers are required.

“We come from the IC world where everything is very rigid,” said Kenneth Larsen, director of 3D-IC product management in Synopsys‘ EDA Group. “On the OSAT side, and maybe this is because it’s so custom, design rules seem like a data sheet. Then you build and optimize the products over time or in collaboration with the OSAT. It’s not an electronic exchange. In the IC world, this would be totally unheard of. While it is possible to tweak a few things, you have a qualification process. And it seems like that’s not there yet for packaging.”

Materials and associated assembly recipes ultimately drive what’s possible for a chiplet-substrate stack in terms of pillar pitch, RDL line widths and spaces, bonding processes, and chiplet placement tolerances. But within a handful of ADKs, there are many possible interactions to consider.

The current focus is on co-optimizing the system design with the chiplet assembly process, leading to an assembly process development flow (see figure 4). This flow considers the needs of customization of an assembly process, and it creates the necessary design rules to be used by package designers.

Fig. 4: Chip-package hybrid flow. Source: ASE

“First you need to define your structure using chiplets. Are you using substrate RDL, 2.5D RDL, or a bridge? After that you need to consider your structure’s materials. What kind of material do you choose to fulfill your electrical performance and the mechanical stress requirements,” said Cao. “After that, you do pre-analysis to ensure all the structures and materials you use are workable in terms of electrical, warpage and mechanical stress.”

The design planning flow also includes the evaluation of die-to-die interconnects through the documents for co-design sign-off.

Conclusion
Before chiplet-based designs can be enabled outside the IDM model, the industry needs to complete the ecosystem that bridges the manufacturing and design complexity. This is because the need to co-optimize the system architecture based on materials, process, and integration capabilities is essential. While this would be easier with a set of well-defined products for the chiplet ecosystem to drive forward on, that has not happened yet.

Engineering teams across the design and manufacturing stack will need to collaborate to choose the appropriate materials, architectures, processes, etc., to develop a final chiplet-based product that is designable. As ASE group’s Cao noted, “An integrated design and manufacturing ecosystem is important. It is very critical to have collaboration among IDM, vendors, materials suppliers. Everyone needs to work together to really enable integration for the real applications.”

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The post What Works Best For Chiplets appeared first on Semiconductor Engineering.

As device scaling slows down, a key system functional integration technology is emerging: heterogeneous integration (HI). It leverages advanced packaging technology to achieve higher functional density and lower cost per function. With the continuous development of major semiconductor applications such as AI HPC, edge AI and autonomous electrical vehicles, traditional chips are transforming into smaller, well-partitioned chiplets that require chip-to-chip interconnections to be denser, faster and more reliable. This boosts the demand for heterogeneous integration, elevating demand for innovative advanced packaging technologies.

HI uses advanced packaging to integrate chiplets with heterogeneous designs and process nodes into a single package. This allows enterprises to choose optimum process nodes for specific system demands, such as 3nm for computing chiplets, 7nm for radio frequency chiplets, or to quickly produce super chips with specific functions in a cost-effective manner. HI not only aims for higher interconnection density, but also integrates various functional components, such as logic chips, sensors, memory, and others, which are needed to complete the whole system in one package. Overall energy efficiency and performance is greatly improved, while package size can be significantly reduced.

Advanced packaging solutions for AI HPC

The typical high-density advanced package size for AI cloud computing processors is 55mm x 55mm or more, and contains a 5-2-5 (top 5 layers, middle 2 layers, bottom 5 layers) advanced substrate, or even up to 11-2-11 wiring layers. Chiplets can be interconnected by fan-out technology with silicon bridge or 2.5D with Si Interposer as the integration platform. Through this technique, industry aims to gain more computing power within the same space.

ASE provides high-density packaging solutions, including Flip Chip Ball Grid Array (FCBGA), Fan Out Chip-on-Substrate (FOCoS), FOCoS-Bridge and 2.5D. The chip-to-chip interconnections in FCBGA is accomplished through BGA substrate, and its minimum L/S (line width/line spacing) is only about 10μm/10μm. The very popular and in-demand CoWoS (Chip on Wafer on Substrate) is a 2.5D packaging technology that uses RDL (redistribution layer) on Si interposer to connect chiplets, and its L/S can be significantly reduced to 0.5μm/0.5μm.

In the Si interposer of a 2.5D package, all the chiplets are connected in a side-by-side arrangement, and as the required number of chiplets increases, its area becomes larger and larger, resulting in fewer and fewer Si interposer chips that can be made from each 12-inch wafer (generally less than 50). This indeed significantly increases the manufacturing cost of 2.5D packaging. However, not all applications require 0.5μm/0.5μm L/S, so ASE came up with FOCoS, which uses fan-out technology’s RDL to integrate different chiplets, and its L/S can reach 2μm/2μm. This gives alternative solutions to the market with lower costs. In addition, ASE’s FOCoS-Bridge technology uses silicon bridge to provide high-density routing for interconnecting different chips (such as logic chips and memory) in areas that require high-speed transmission and uses Fan-Out RDL to integrate in other areas. As such, it delivers both 0.5μm/0.5μm and 2μm/2μm flexibility in L/S design, while achieving a significant increase in packaging density and bandwidth.

High performance chip-package-system co-design

To achieve the aforementioned high bandwidth, the chip, package, and entire system must be designed together to achieve holistic design optimization instead of just considering the individual parts. When using electronic design automation (EDA) for design optimization, consideration must be given to overall signal change along the entire transmission path, including Cu pillar, RDL fine line, TSV, μbump, etc. Eye diagrams can then be used to analyze the SerDes link’s electrical performance. When designing differential pairs for high-speed signals, it is necessary to reduce return and insertion loss, especially in the operating frequency band. From chip to package to the entire system, Taiwan’s manufacturing advantage lies in the ability to accomplish the turnkey design process, from beginning to end.

Providing more computing power with less energy

The industry is currently focused on optimizing energy efficiency. One of the key questions being asked is whether the power regulation and decoupling components, which were previously located on the system board, can be moved closer to the package or processor chip. There is even talk of redesigning the on-chip power delivery network (PDN), including supplying power directly from the backside of the chip (Backside PDN).

Power integrity design for power delivery network (PDN)

Optimizing power integrity and minimizing noise can be achieved by strategically positioning the capacitor. Ideally, the capacitor should be placed as close to the chip as possible, but this is dependent on the capacitor’s size and the manufacturing process, both of which can impact cost and performance. Traditional surface-mount technology (SMT) capacitors are relatively large, but chip-level silicon capacitors (Si-Cap) are now available that offer decent capacitance values.

UCIe (Universal Chiplet Interconnect Express) Consortium

Traditionally, there are many standard communication protocols (such as Block-to-Block, Memory Bus, or Interconnection Interface Protocols) at the chip level and the board level for system designers. Industry protocols that specify package-level integration are growing, especially given the need for a universal interface for chiplet integration using 2.5D and FOCoS packaging technologies.

In March 2022, Intel invited upstream and downstream manufacturers in the semiconductor industry chain to form the UCIe Consortium, and a standardized data transmission architecture for chiplet integration was introduced to reduce the cost of advanced packaging design. ASE is proud to be a founding member (Promoter member).

ASE offers a diverse range of advanced packaging types. We have developed packaging design specifications that can be integrated with foundry solutions specifications as well as the system requirements of original equipment manufacturers (OEMs) and cloud service providers to create a comprehensive UCIe package standard. The standard can assist in realizing ubiquitous chiplet heterogeneous integration for HPC applications using various advanced packaging technology architectures, such as 2.5D, 3D, FOCoS, Fan-out, EMIB, CoWoS, etc. Headquartered in Taiwan, ASE is enthusiastically participating in the formulation of international standards and relentlessly providing integrated solutions to the global industry.

Heterogeneous integration has been in development for many years. It can be used to integrate not only homogeneous and heterogeneous chiplets but also other passive and active components including connectors, into a single package. Achieving this requires not only advanced packaging technologies but also design and testing coordination. ASE offers a comprehensive one-stop service solution that includes system design, packaging, and testing to help customers shorten chip design cycles and accelerate product innovation.

The post Advanced Packaging Design For Heterogeneous Integration appeared first on Semiconductor Engineering.

The semiconductor industry is preparing for the migration from proprietary chiplet-based systems to a more open chiplet ecosystem, in which chiplets fabricated by different companies of various technologies and device nodes can be integrated in a single package with acceptable yield.

To make this work as expected, the chip industry will have to solve a variety of well-documented technical and business issues, and it will have to rein in some of the grander visions of what’s possible — at least initially. The basic challenge is aligning domain-specific performance demands of end systems, which contain a growing number of chiplets, with the assembly and packaging capabilities and methodologies of IDMs, foundries, and OSATs. This includes the creation of assembly development kits (ADKs) that are roughly the equivalent of process development kits (PDKs), which today are codified with manufacturing specifications.

A PDK provides the appropriate level of detail needed to develop planar chips, marrying design tools with fab processes to achieve a predictable outcome. But making this work for an ADK with heterogeneous chiplets is many times more complex. Design and assembly teams need to manage thermal, mechanical, and electrical co-dependencies that cause electrical and mechanical stress, resulting in warpage, reduced yield, and reliability issues under real-world workloads. Layered on top of this the business and legal issues related to packaging of different devices from different manufacturers.

“Chiplets are a growing trend, especially in the HPC and networking segments, with potential to scale to other applications,” said Gabriela Pereira, technology and market analyst for semiconductor packaging at Yole Intelligence. “The industry has understood that high-end advanced packaging technologies are needed to connect them — but that’s much more complex than it seems. Connecting chiplets requires the design of high-bandwidth interconnections at the package level, which can take different forms — e.g., 2D, 2.5D or 3D — while ensuring that the thermal and power requirements are fulfilled.”

Commercial chiplet-based devices generally are domain-specific, and sometimes developed for a specific workload. So despite a big industry push to create a LEGO-like mix-and-match ecosystem for chiplets — which today includes multiple IP and EDA vendors, foundries, memory suppliers, OSATs, substrate suppliers, etc. — making this work as planned will require time and a massive amount of work.

Fig. 1: System assembly requires tighter coupling between chipmakers and OSATs. Source: ASE

In creating heterogeneous integrated designs, it’s essential to have much tighter collaboration between foundries, IDMs, OSATs, and PCB manufacturers. And because each chiplet-based system will be customized, the number of assembly processes will grow substantially. For example, one OSAT noted that among its ~5,000 customers, there are ~1,000 different assembly processes.

That diversity in products and processes makes it difficult to achieve predictable results by choosing chiplets from a large menu of options.

“We’ve already encountered a lot of limitations including not only the silicon, but also integration and the ecosystem,” said Lihong Cao, senior director at ASE Group, at MEPTEC’s Road to Chiplets forum. She stressed that customers continue to push for a low-cost chiplet assembly process, which is creating constructive tension between developing a sophisticated assembly process and the economic realities of different industry sectors. Computing devices for automotive have a higher cost sensitivity than for data centers, for example, but their chips operate in a harsher environment over a longer lifetime.

What’s needed is a defined set of assembly process recipes — basically, a highly limited menu of choices — that are specific to the end application (HPC, automotive, RF telecommunications) in order to lower the cost of chiplet-based systems. OSATs and foundries already are moving in that direction for high-performance computing. For example, at its 2024 Direct Connect event, Intel shared its six different package processes for chiplets. TSMC and Samsung also offer defined sets of chiplet processes. But the success of these assembly processes requires engineering teams to co-optimize the flows, processes, and materials to best match the system requirements.

Fig. 2: Integrated platform development requires tightly coupled architectural analysis that co-optimizes the system design to architecture to assembly process and packaging material selections. Source: Applied Materials

“Previously, when we designed a system we only had to be worried about the system requirements. Once we start segregating into dies and reassembling them, we have to start looking at other things. We have to worry about putting them together while considering signal integrity between dies, reliability, thermals, etc.,” said Itai Leshniak, director of AI systems solutions at Applied Materials, at the MEPTEC forum. “If we take the case of AI-based computer vision, we can break it down layer by layer — on the hardware side, determining which computer vision processors, sensors, filters are needed to break it down into the architecture at layer. Then we begin to go through how to package all these chiplets, and then which materials to use and how to take advantage of those materials.”

Materials and assembly processes
Conceptually, design engineers will use chiplets to design a system. However, the co-design and integration is far more complicated than assembling a set of LEGO blocks, because the chiplets, interposers, and package substrates come from different design houses and manufacturing facilities. The advanced packaging technologies used to connect chiplets vary with an alphabet soup of names — FOWLP, FOPLP, CoWoS, etc., each of which poses additional design and material choices along with certain process limitations.

Fig. 3: There are a multitude of choices in multi-die packaging from the high-level layout to substrates, materials, bonding methods, and cooling materials. Source: Synopsys

Currently engineering teams determine the tradeoffs among the different packaging options to select materials, derive a process recipe, and determine design rules.

Materials are a good starting point. “Materials are very important because they enable new products and packaging technologies,” Tanja Braun, deputy group manager at the Fraunhofer Institute for Reliability and Microintegration IZM. “As you move into more advanced packaging, process is getting much more complex because you are putting more things together. In the end, it’s a combination of equipment, materials, and process development.”

There are three thermal parameters that are critical in package assembly processes — coefficients of thermal expansion (CTE), glass transition temperature (T_g), and thermal conductivity. These factors affect how a material behaves in manufacturing to packaging processes, as well as how it behaves in the field.

“Challenges for our materials include temperature limitations of different die,” said Rama Puligadda, CTO at Brewer Science. “We have to ensure that the temperatures used for bonding materials don’t exceed the thermal limitations of any of the chips that are being integrated into the package. Additionally, there may be some subsequent processes like redistribution layer (RDL) formation or molding. Our materials have to survive those processes. They have to survive the chemicals they come in contact with throughout the packaging process scheme. Mechanical stresses in the package add additional challenges for bonding materials.”

Within a stack of chiplets-on-substrate with an optional interposer, their material attributes affect the thermal-mechanical stresses between neighboring materials, as well. This directly impacts interconnect dimensional control over a large area substrate area.

“If you go work the numbers, you will find that the level of tolerance and control required is frightening,” said Dick Otte, CEO of Promex Industries. “You’re talking about controlling dimensions equivalent to the width of a grass blade over the length of a football field, so that’s roughly 1 in 100,000.”

The goal is uniform heating of the structure in reflow in order to attain the best process results and to avoid cracking. “When you’re taking it through a 250 degrees centigrade temperature change, then you need to heat up slowly so that the top doesn’t get hot before the bottom does,” said Otte.

Multi-physics to comprehend co-optimization
Multi-physics modeling has become the go-to method for co-optimizing packaging design and assembly process development. That affects both permanent and temporary materials, as well the placement of processors, memories, and other components.

“You always looking to what the customer needs electrically, because that’s going to help define the material set. The material set is broadly applicable to a bunch of speed ranges. As long as you don’t step outside of those electrical specifications, theoretically you should be okay,” said Mike Kelly, vice president of advanced package and technology integration at Amkor Technology.

To save many iterations of empirically based development, engineers can use physics-based simulations to understand the impact of a material set’s properties impact on the assembly process, power/thermals, and mechanical vibrations.

Consider that HPC chiplet products can consume ~1,000 watts at peak performance so the power and thermal interactions need to be fully understood.

“We’ve struggled, as everybody has, with this blizzard of complexity in the different techniques. Not only do they vary across different vendors, but they’re also varying over time,” said Marc Swinnen, director of product marketing at Ansys. “Our approach has been to identify the essentials that need to be worked on. We work jointly with customers to develop a simulation flow that actually achieves what is needed now.”

Materials are just one piece of the puzzle. “Then there’s the assembly stresses that need to be modeled to know whether you can correctly assemble this device. The third one is mechanical vibration,” Swinnen said. “Can your device withstand those regular vibrations? Modeling these attributes ties directly into our mechanical analysis tools — acoustic, thermal, vibration, etc. In the end, you’re going to have to do physics simulation. We’re trying to make it accessible to people in many different forms. But the bedrock of our tool offerings is that we have the meshing simulation and analysis. It’s a question of getting the data in the right format in a way that’s practical and usable.”

Evolving assembly design kits
For conventional packages, OSATs provide design rules for each packaging technology. These need to consider electrical, mechanical and thermal design requirements and manufacturing process limitations. In effect this is a multi-dimensional bounding box. Suppliers perform iterations with the customer to create a product specific process recipe.

Rules cover the macro-level attributes. “At a minimum, what you see from design rules is maximum package size, maximum silicon size, and whether silicon can be [mounted] on both sides of the substrate, such that when you follow these constructions the final product will have a lifetime of 1,000 thermal cycles, for example,” said Fraunhofer’s Braun.

In addition, design rules need to describe routing constraints for the interposer and/or redistribution layer, such as RDL line widths and spaces, ball-grid/pillar/pad size and pitches, and the maximum number of interconnections.

Breaking up a monolithic HPC device into multiple dies shifts some of the semiconductor design/process complexity into the packaging space. That makes things much more complicated. Consider that to connect 10 dies requires on order of 100,000 traces within the interposer’s or substrate’s redistribution layer.

To cope with the complexity at the chip level, the IC industry has long relied upon process design kits (PDKs) to capture design rules in an electronic file that can be imported into EDA tools. Their counterparts, assembly design kits (ADKs), are relatively immature.

“We call it Smart Package,” said Amkor’s Kelly. “It’s an ADK that we give to every customer who’s doing their own design. It is a set of macros, and a customization of a database tailored to a customer’s particular design. For chiplets, it is a high-density fan-out package technology. And it’s cognizant of the limitations for metal density and metal spacing, etc. This makes it easier for us to do design rule checks (DRCs).”

But right now, with the level of customization still required, how an ADK is derived and what it entails is in flux. Partnerships between EDA tool vendors, OSATs, and semiconductor device providers are required.

“We come from the IC world where everything is very rigid,” said Kenneth Larsen, director of 3D-IC product management in Synopsys‘ EDA Group. “On the OSAT side, and maybe this is because it’s so custom, design rules seem like a data sheet. Then you build and optimize the products over time or in collaboration with the OSAT. It’s not an electronic exchange. In the IC world, this would be totally unheard of. While it is possible to tweak a few things, you have a qualification process. And it seems like that’s not there yet for packaging.”

Materials and associated assembly recipes ultimately drive what’s possible for a chiplet-substrate stack in terms of pillar pitch, RDL line widths and spaces, bonding processes, and chiplet placement tolerances. But within a handful of ADKs, there are many possible interactions to consider.

The current focus is on co-optimizing the system design with the chiplet assembly process, leading to an assembly process development flow (see figure 4). This flow considers the needs of customization of an assembly process, and it creates the necessary design rules to be used by package designers.

Fig. 4: Chip-package hybrid flow. Source: ASE

“First you need to define your structure using chiplets. Are you using substrate RDL, 2.5D RDL, or a bridge? After that you need to consider your structure’s materials. What kind of material do you choose to fulfill your electrical performance and the mechanical stress requirements,” said Cao. “After that, you do pre-analysis to ensure all the structures and materials you use are workable in terms of electrical, warpage and mechanical stress.”

The design planning flow also includes the evaluation of die-to-die interconnects through the documents for co-design sign-off.

Conclusion
Before chiplet-based designs can be enabled outside the IDM model, the industry needs to complete the ecosystem that bridges the manufacturing and design complexity. This is because the need to co-optimize the system architecture based on materials, process, and integration capabilities is essential. While this would be easier with a set of well-defined products for the chiplet ecosystem to drive forward on, that has not happened yet.

Engineering teams across the design and manufacturing stack will need to collaborate to choose the appropriate materials, architectures, processes, etc., to develop a final chiplet-based product that is designable. As ASE group’s Cao noted, “An integrated design and manufacturing ecosystem is important. It is very critical to have collaboration among IDM, vendors, materials suppliers. Everyone needs to work together to really enable integration for the real applications.”

Related stories
Fan-Out Packaging Gets Competitive
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Inside Panel-Level Fan-Out Technology
Fraunhofer’s panel experts dig into why this approach is needed and where the challenges are to making it work.

Next Steps For Panel-Level Packaging
Where it’s working, and what challenges remain for even broader adoption.

Mini-Consortia Forming Around Chiplets
Commercial chiplet marketplaces are still on the distant horizon, but companies are getting an early start with more limited partnerships.

What Can Go Wrong In Heterogeneous Integration
Workflows and tools are disconnected, mechanical stress is ill-defined, and complete co-planarity is nearly impossible. But there are solutions on the horizon.

Mechanical Challenges Rise With Heterogeneous Integration
But gaps in tools make it difficult to address warpage, structural issues, and new materials in multi-die/multi-chiplet designs.

The post What Works Best For Chiplets appeared first on Semiconductor Engineering.

As device scaling slows down, a key system functional integration technology is emerging: heterogeneous integration (HI). It leverages advanced packaging technology to achieve higher functional density and lower cost per function. With the continuous development of major semiconductor applications such as AI HPC, edge AI and autonomous electrical vehicles, traditional chips are transforming into smaller, well-partitioned chiplets that require chip-to-chip interconnections to be denser, faster and more reliable. This boosts the demand for heterogeneous integration, elevating demand for innovative advanced packaging technologies.

HI uses advanced packaging to integrate chiplets with heterogeneous designs and process nodes into a single package. This allows enterprises to choose optimum process nodes for specific system demands, such as 3nm for computing chiplets, 7nm for radio frequency chiplets, or to quickly produce super chips with specific functions in a cost-effective manner. HI not only aims for higher interconnection density, but also integrates various functional components, such as logic chips, sensors, memory, and others, which are needed to complete the whole system in one package. Overall energy efficiency and performance is greatly improved, while package size can be significantly reduced.

Advanced packaging solutions for AI HPC

The typical high-density advanced package size for AI cloud computing processors is 55mm x 55mm or more, and contains a 5-2-5 (top 5 layers, middle 2 layers, bottom 5 layers) advanced substrate, or even up to 11-2-11 wiring layers. Chiplets can be interconnected by fan-out technology with silicon bridge or 2.5D with Si Interposer as the integration platform. Through this technique, industry aims to gain more computing power within the same space.

ASE provides high-density packaging solutions, including Flip Chip Ball Grid Array (FCBGA), Fan Out Chip-on-Substrate (FOCoS), FOCoS-Bridge and 2.5D. The chip-to-chip interconnections in FCBGA is accomplished through BGA substrate, and its minimum L/S (line width/line spacing) is only about 10μm/10μm. The very popular and in-demand CoWoS (Chip on Wafer on Substrate) is a 2.5D packaging technology that uses RDL (redistribution layer) on Si interposer to connect chiplets, and its L/S can be significantly reduced to 0.5μm/0.5μm.

In the Si interposer of a 2.5D package, all the chiplets are connected in a side-by-side arrangement, and as the required number of chiplets increases, its area becomes larger and larger, resulting in fewer and fewer Si interposer chips that can be made from each 12-inch wafer (generally less than 50). This indeed significantly increases the manufacturing cost of 2.5D packaging. However, not all applications require 0.5μm/0.5μm L/S, so ASE came up with FOCoS, which uses fan-out technology’s RDL to integrate different chiplets, and its L/S can reach 2μm/2μm. This gives alternative solutions to the market with lower costs. In addition, ASE’s FOCoS-Bridge technology uses silicon bridge to provide high-density routing for interconnecting different chips (such as logic chips and memory) in areas that require high-speed transmission and uses Fan-Out RDL to integrate in other areas. As such, it delivers both 0.5μm/0.5μm and 2μm/2μm flexibility in L/S design, while achieving a significant increase in packaging density and bandwidth.

High performance chip-package-system co-design

To achieve the aforementioned high bandwidth, the chip, package, and entire system must be designed together to achieve holistic design optimization instead of just considering the individual parts. When using electronic design automation (EDA) for design optimization, consideration must be given to overall signal change along the entire transmission path, including Cu pillar, RDL fine line, TSV, μbump, etc. Eye diagrams can then be used to analyze the SerDes link’s electrical performance. When designing differential pairs for high-speed signals, it is necessary to reduce return and insertion loss, especially in the operating frequency band. From chip to package to the entire system, Taiwan’s manufacturing advantage lies in the ability to accomplish the turnkey design process, from beginning to end.

Providing more computing power with less energy

The industry is currently focused on optimizing energy efficiency. One of the key questions being asked is whether the power regulation and decoupling components, which were previously located on the system board, can be moved closer to the package or processor chip. There is even talk of redesigning the on-chip power delivery network (PDN), including supplying power directly from the backside of the chip (Backside PDN).

Power integrity design for power delivery network (PDN)

Optimizing power integrity and minimizing noise can be achieved by strategically positioning the capacitor. Ideally, the capacitor should be placed as close to the chip as possible, but this is dependent on the capacitor’s size and the manufacturing process, both of which can impact cost and performance. Traditional surface-mount technology (SMT) capacitors are relatively large, but chip-level silicon capacitors (Si-Cap) are now available that offer decent capacitance values.

UCIe (Universal Chiplet Interconnect Express) Consortium

Traditionally, there are many standard communication protocols (such as Block-to-Block, Memory Bus, or Interconnection Interface Protocols) at the chip level and the board level for system designers. Industry protocols that specify package-level integration are growing, especially given the need for a universal interface for chiplet integration using 2.5D and FOCoS packaging technologies.

In March 2022, Intel invited upstream and downstream manufacturers in the semiconductor industry chain to form the UCIe Consortium, and a standardized data transmission architecture for chiplet integration was introduced to reduce the cost of advanced packaging design. ASE is proud to be a founding member (Promoter member).

ASE offers a diverse range of advanced packaging types. We have developed packaging design specifications that can be integrated with foundry solutions specifications as well as the system requirements of original equipment manufacturers (OEMs) and cloud service providers to create a comprehensive UCIe package standard. The standard can assist in realizing ubiquitous chiplet heterogeneous integration for HPC applications using various advanced packaging technology architectures, such as 2.5D, 3D, FOCoS, Fan-out, EMIB, CoWoS, etc. Headquartered in Taiwan, ASE is enthusiastically participating in the formulation of international standards and relentlessly providing integrated solutions to the global industry.

Heterogeneous integration has been in development for many years. It can be used to integrate not only homogeneous and heterogeneous chiplets but also other passive and active components including connectors, into a single package. Achieving this requires not only advanced packaging technologies but also design and testing coordination. ASE offers a comprehensive one-stop service solution that includes system design, packaging, and testing to help customers shorten chip design cycles and accelerate product innovation.

The post Advanced Packaging Design For Heterogeneous Integration appeared first on Semiconductor Engineering.

Defining whether a 2.5D device is a printed circuit board shrunk down to fit into a package, or is a chip that extends beyond the limits of a single die, may seem like hair-splitting semantics, but it can have significant consequences for the overall success of a design.

Planar chips always have been limited by size of the reticle, which is about 858mm². Beyond that, yield issues make the silicon uneconomical. For years, that has limited the number of features that could be crammed onto a planar substrate. Any additional features would need to be designed into additional chips and connected with a printed circuit board (PCB).

The advent of 2.5D packaging technology has opened up a whole new axis for expansion, allowing multiple chiplets to be interconnected inside an advanced package. But the starting point for this packaged design can have a big impact on how the various components are assembled, who is involved, and which tools are deployed and when.

There are several reasons why 2.5D is gaining ground today. One is cost. “If you can build smaller chips, or chiplets, and those chiplets have been designed and optimized to be integrated into a package, it can make the whole thing smaller,” says Tony Mastroianni, advanced packaging solutions director at Siemens Digital Industries Software. “And because the yield is much higher, that has a dramatic impact on cost. Rather than having 50% or below yield for die-sized chips, you can get that up into the 90% range.”

Interconnecting chips using a PCB also limits performance. “Historically, we had chips packaged separately, put on the PCB, and connected with some routing,” says Ramin Farjadrad, CEO and co-founder of Eliyan. “The problems people started to face were twofold. One was that the bandwidth between these chips was limited by going through the PCB, and then a limited number of balls on the package limited the connectivity between these chips.”

The key difference with 2.5D compared to a PCB is that 2.5D uses chip dimensions. There are much finer-grain wires, and various components can be packed much closer together on an interposer or in a package than on a board. For those reasons, wires can be shorter, there can be more of them, and bandwidth is increased.

That impacts performance at multiple levels. “Since they are so close, you don’t have the long transport RC or LC delays, so it’s much faster,” says Siemens’ Mastroianni. “You don’t need big drivers on a chip to drive long traces over the board, so you have lower power. You get orders of magnitude better performance — and lower power. A common metric is to talk about pico joules per bit. The amount of energy it takes to move bits makes 2.5D compelling.”

Still, the mindset affects the initial design concept, and that has repercussions throughout the flow. “If you talk to a die designer, they’re probably going to say that it is just a big chip,” says John Park, product management group director in the Custom IC & PCB Group at Cadence. “But if you talk to a package designer, or a board designer, they’re going to say it’s basically a tiny PCB.”

Who is right? “The internal organizational structure within the company often decides how this is approached,” says Marc Swinnen, director of product marketing at Ansys. “Longer term, you want to make sure that your company is structured to match the physics and not try to match the physics to your company.”

What is clear is that nothing is certain. “The digital world was very regular in that every two years we got a new node that was half size,” says Cadence’s Park. “There would be some new requirements, but it was very evolutionary. Packaging is the Wild West. We might get 8 new packaging technologies this year, 3 next year, 12 the next year. Many of these are coming from the foundries, whereas it used to be just from the outsourced semiconductor assembly and test companies (OSATs) and the substrate providers. While the foundries are a new entrant, the OSATs are offering some really interesting packaging technologies at a lower cost.”

Part of the reason for this is that different groups of people have different requirement sets. “The government and the military see the primary benefits as heterogeneous integration capabilities,” says Ansys’ Swinnen. “They are not pushing the edge of processing technology. Instead, they are designing things like monolithic microwave integrated circuits (MMICs), where they need waveguides for very high-speed signals. They approach it from a packaging assembly point of view. Conversely, the high-performance compute (HPC) companies approach it from a pile of 5nm and 3nm chips with high performance high-bandwidth memory (HBM). They see it as a silicon assembly problem. The benefit they see is the flexibility of the architecture, where they can throw in cores and interfaces and create products for specific markets without having to redesign each chiplet. They see flexibility as the benefit. Military sees heterogeneous integration as the benefit.”

Materials
There are several materials used as the substrate in 2.5D packaging technology, each of which has different tradeoffs in terms of cost, density, and bandwidth, along with each having a selection of different physical issues that must be overcome. One of the primary points of differentiation is the bump pitch, as shown in figure 1.

Fig 1. Chiplet interconnection for various substrate configurations. Source: Eliyan

When talking about an interposer, it generally is considered to be silicon. “The interposer could be a large piece of silicon (Fig 1 top), or just silicon bridges between the chips (Fig 1 middle) to provide the connectivity,” says Eliyan’s Farjadrad. “Both of these solutions use micro-bumps, which have high density. Interposers and bridges provide a lot of high-density bumps and traces, and that gives you bandwidth. If you utilize 1,000 wires each running at 5Gb, you get 5Tb. If you have 10,000, you get 50Tb. But those signals cannot go more than two or three millimeters. Alternatively, if you avoid the silicon interposer and you stay with an organic package (Fig 1 bottom), such as flip chip package, the density of the traces is 5X to 10X less. However, the thickness of the wires can be 5X to 10X more. That’s a significant advantage, because the resistance of the wires will go down by the square of the thickness of the wires. The cross section of that wire goes up by the square of that wire, so the resistance comes down significantly. If it’s 5X less density, that means you can run signals almost 25X further.”

For some people, it is all about bandwidth per millimeter. “If you have a parallel bus, or a parallel interface that is high speed, and you want bandwidth per millimeter, then you would probably pick a silicon interposer,” says Kent Stahn, senior manager of hardware engineering in Synopsys‘ Solutions Group. “An organic substrate is low-loss, low-cost, but it doesn’t have the density. In between, there are a bunch of solutions that deliver on some of that, but not for the same cost.”

There are other reasons to pick a substrate material, as well. “Silicon interposer comes from a foundry, so availability is a problem,” says Manuel Mota, senior staff product manager in Synopsys’ Solutions Group. “Some companies are facing challenges in sourcing advanced packages because capacity is taken. By going to other technologies that have a little less bandwidth density, but perhaps enough for your application, you can find them elsewhere. That’s becoming a critical aspect.”

All of these technologies are progressing rapidly, however. “The reticle limit is about 858mm square,” says Park. “People are talking about interposers that are perhaps four times that size, but we have laminates that go much bigger. Some of the laminate substrates coming from Japan are approaching that same level of interconnect density that we can get from silicon. I personally see more push towards organic substrates. Chip-on-Wafer-on-Substrate (CoWoS) from TSMC uses a silicon interposer and has been the technology of choice for about 12 years. More recently they introduced CoWoS-R, which uses film polyamide, closer to an organic type of substrate. Now we hear a lot about glass substrates.”

Over time, the total real estate inside the package may grow. “It doesn’t make sense for foundries to continue to build things the size of a 30-inch printed circuit board,” adds Park. “There are materials that are capable of addressing the bigger designs. Where we really need density is die-to-die. We want those chiplets right next to each other, a couple of millimeters of interconnect length. We want things very short. But the rest of it is just fanning out the I/O so that it connects to the PCB.”

This is why bridges are popular. “We do see a progression to bridges for the high-speed part of the interface,” say Synopsys’ Stahn. “The back side of it would be fanout, like RDL fanout. We see RDL packages that are going to be more like traditional packages going forward.”

Interposers offer additional capabilities. “Today, 99% of the interposers are passive,” says Park. “There’s no front end of line, there are no device layers. It’s purely back end of line processing. You are adding three, four, five metal layers to that silicon. That’s what we call a passive interposer. It’s just creating that die-to-die interconnect. But there are people taking that die and making it an active interposer, basically adding logic to that.”

That can happen for different purposes. “You already see some companies doing active interposers, where they add power management or some of the controls logic,” says Mota. “When you start putting active circuits on interposer, is it still a 2.5D integration, or does it become a 3D integration? We don’t see a big trend toward active interposers today.”

There are some new issues, though. “You have to consider coefficients of thermal expansion (CTE) mismatches,” says Stahn. “This happens whenever two materials with different CTEs are bonded together. Let’s start with the silicon interposer. You can get higher wattage systems, where the SoCs can be talking to their peers, and that can consume a lot of power. A silicon interposer still has to go in a package. The CTE mismatches are between the silicon to the package material. And with the bridge, you’re using it where you need it, but it’s still silicon die-to-die. You have to do the thermal mechanical analysis to make sure that the power that you’re delivering, and the CTE mismatches that you have, result in a viable system.”

While signal lengths in theory can get longer, this poses some problems. “When you’re making those long connections inside a chip, you typically limit those routes to a couple of millimeters, and then you buffer it,” says Mastroianni. “The problem with a passive silicon interposer is there are no buffers. That can really become a serious issue. If you do need to make those connections, you need to plan those out very carefully. And you do need to make sure you’re running timing analysis. Typically, your package guys are not going to be doing that analysis. That’s more of a problem that’s been solved with static timing analysis by silicon engineers. We do need to introduce an STA flow and deal with all the extractions that include organic and silicon type traces, and it becomes a new problem. When you start getting into some of those very long traces, your simple RC timing delays, which are assumed in normal STA delay calculators, don’t account for some of the inductance and mutual inductance between those traces, so you can get serious accuracy issues for those long traces.”

Active interposers help. “With active interposers, you can overcome some of the long-distance problems by putting in buffers or signal repeaters,” says Swinnen. “Then it starts looking more like a chip again, and you can only do it on silicon. You have the EMIB technology from Intel, where they embedded chiplet into the interposer and that’s an active bridge. The chip talks to the EMIB chip, and they both talk to you through this little active bridge chip, which is not exactly an active interposer, but acts almost like an active interposer.”

But even passive components add value. “The first thing that’s being done is including trench capacitors in the interposer,” says Mastroianni. “That gives you the ability to do some good decoupling, where it counts, close to the die. If you put them out on the board, you lose a lot of the benefits for the high-speed interfaces. If you can get them in the interposer, sitting right under where you have the fast-switching speed signals, you can get some localized decoupling.”

In addition to different materials, there is the question of who designs the interposer. “The industry seems to think of it as a little PCB in the context of who’s doing the design,” says Matt Commens, senior manager for product management at Ansys. “The interposers are typically being designed by packaging engineers, even though they are silicon processes. This is especially true for the high-performance ones. It seems counterintuitive, but they have that signal integrity background, they’ve been designing transmission lines and minimizing mismatch at interconnects. A traditional IC designer works from a component point of view. So certainly, the industry is telling us that the people they’re assigning to do that design work are packaging type of personas.”

Power
There are some considerable differences in routing between PCBs and interposers. “Interposer routing is much easier, as the number of components is drastically reduced compared to the PCB,” says Andy Heinig, head of department for efficient electronics at Fraunhofer IIS/EAS. “On the other hand, the power grid on the interposer is much more complex due to the higher resistance of the metal layers and the fact that the power grid is cut out by signal wires. The routing for the die-to-die interface is more complex due to the routing density.”

Power delivery looks very different. “If you look at a PCB, they put these big metal pour areas embedded in the layers, and they void out areas where things need to go through,” says Park. “You put down a bunch of copper and then you void out the others. We can’t build an interposer that way. We have to deposit the interconnect, so the power and ground structures on a silicon interposer will look more like a digital chip. But the signal will look more like a PCB or laminate package.”

Routing does look more like a PCB than a chip. “You’ll see things like teardrops or fillets where it makes a connection to a pad or via to create better yield,” adds Park. “The routing styles today are more aligned to PCBs than they are to a digital IC, where you just have 90° orthogonal corners and clean routing channels. For interposers, whether it’s silicon or organic, the via is often bigger than the wire, which is a classic PCB problem. The routers, if we’re talking about digital, is again more like a small PCB than a die.”

TSVs can create problems, too. “If you’re going to treat them as square, you’re losing a lot of space at the corners,” says Swinnen. “You really want 45° around those objects. Silicon routers are traditionally Manhattan, although there has been a long tradition of RDL routing, which is the top layer where the bumps are connected. That has traditionally used octagonal bumps or round bumps, and then 45° routing. It’s not as flexible as the PCB routing, but they have redistribution layer routers, and also they have some routers that come from the full custom side which have full river routing.”

Related Reading
True 3D Is Much Tougher Than 2.5D
While terms often are used interchangeably, they are very different technologies with different challenges.
Thermal Integrity Challenges Grow In 2.5D
Work is underway to map heat flows in interposer-based designs, but there’s much more to be done.

The post 2.5D Integration: Big Chip Or Small PCB? appeared first on Semiconductor Engineering.