Architectural Design

The first stage in the design process for a system involving heterogeneous integration ("HI") is not dissimilar to the design of a traditional electronic system. Like any systems design challenge the same activities of understanding the requirements for the proposed system, any operational constraints, and all the normal design considerations need to be considered. Just as in many other design disciplines, be that car design, house design, etc. how the designer makes best use of HI to bring together all the constituent parts needed to deliver the overall system concept is often guided by a clear architectural design for the system.

Fundamentally the design process is still one of combining a set of component parts with different functions and material compositions into a single, compact system.  What changes in a HI system are the resources used to form the desired system and some of the tools and techniques needed to design, verify and assemble it. 

HI Systems within the electronics market

Traditional semiconductor packaging provides protection from mechanical, thermal and electrical stress and also a clear separation between the component parts of a system, leaving the system designers the task of selecting parts based on their external data sheet and designing interconnection schemes between the functional parts of the system. HI is simply the latest iteration of innovation in materials, fabrication processes, tooling, standards and design support that offer new forms of electronic system architectures compared to the traditional Printed Circuit Board populated with packaged components to better meet the key drivers within the electronics industry.

From a manufacturing perspective there has been a separation between the die producing semiconductor foundries and the semiconductor package, assembly and test activities. Design IP companies could either license their IP to be integrated into a third party die or fabricate and package their IP and sell component parts to systems designers and/or electronic systems contract manufacturers.

Use of evolving Standards

The electronic systems industry has since its formation looked to reduce the burden of systems design by supporting a market for component parts and standards based interfaces that can be easily combined within design tools to form systems designs that can be sent to production facilities to manufacture in volume. The move to heterogenous integration of bare die or chiplets is just a continued evolution of the electronic systems market.  

Part of any architectural design for a system has to involve a choice of which standards to adopt for a specific system design.

The development of industry standards enables the electronics industry to create very efficient product design and manufacturing supply chains. Standards cover almost every design aspect of an electronic system, such as mechanical properties, electrical properties, components, materials, thermal management as well as the processes of design such as test methods and ensuring product safety.  

System design complexity

Advances in packaging technologies are breaking down many of the traditional package separations giving designers both new opportunities for design optimisation but also the challenges associated with them.  One of the hoped for benefits of HI is Architecture exploration of multi-die systems.

System disaggregation 

Integrated Circuit design and advances in semiconductor fabrication have enabled greater amounts of system function to be combined into a single semiconductor device. The industry has formed into a range of suppliers, some are IP design companies who don't manufacture their IP but license it to semiconductor device manufacturers who combine various IP blocks into sub-systems or complete System On Chip offerings. 

One proposed use for Chiplets is to re-partition monolithic designs so that instead of manufacturing the sub-system or system on chip as a single die it is partitioned across several die that are brought together into a system using advanced packaging techniques. HI does offer a path for IP design companies to move from a licensing business model to offering their IP as a chiplet. 

Heterogenous integration 

One proposed use for Chiplets is to allow the combination of parts from many different semiconductor foundry processes into a system. Today this would be achieved by assembling many packaged parts from different suppliers.  

Convergence of tool support

HI based systems design brings a growing number of design considerations which leads to demand for multi-domain design support (chip, package, board)  and multi-physics (thermal, optical, electrical, mechanical) understanding within the systems design space. This is leading to the integration of more design aid models, tools and methodologies by major Electronic Design Automation companies.

Part of the standards setting is establishing common formats to share design information between product designers, manufacturing, assembly, and test facilities. This enables software systems to help optimise the supply chain for electronic systems. Again HI is causing new standards setting activity. Various parties are proposing interchange formats to the standards bodies for ratification.  Design tool vendors are already supporting major manufacturers specific design information formats and will converge them as standards develop. These include TSMC’s 3Dblox, Samsung’s 3D CODE, Chiplet Data XML (CDXML) from the Open Compute Project, etc.

Model based design is now a fundamental design method, using many computational models throughout the design process to support the design team to deliver complex systems. The major tool vendors are combining computational models and enabling exchange of design information between them to better support the design process. 

Interconnection fabric

Just as a traditional electronic system design requires the selection of an appropriate PCB laminate material on which to place all the component parts of the system, a HI based design needs to determine the appropriate substrate. Some design considerations come from the operating environment while others from the system functions, for example flexibility of the substrate or the need to support dense high speed signals.

Pathways to manufacture 

Some of the changes introduced by HI will require a change in manufacturing supply chains. Every reducing manufacturing process tolerances in terms of via widths, via alignment, line width variation, dielectric thickness variation are demanding ever more specialised manufacturing capability and higher capital investment.