MCM Packaging

Key Takeaways

• MCM packaging offers power efficiency, reliability, streamlined design, and cost-effectiveness by integrating multiple chips onto a unified substrate.

• Recent advancements in MCM packaging include organic substrates, redistribution layer fan-out, silicon interposers, and hybrid bonding.

• These technologies enable improved signal integrity, enhanced performance, and efficient power distribution in MCM designs.

An MCM can contain a variety of different technologies

Multi-chip module (MCM) packaging has emerged as a crucial technology in the field of electronic assemblies and chip packaging. By integrating multiple integrated circuits (ICs), semiconductor dies, and discrete components onto a unifying substrate, MCMs provide a compact and efficient solution that can be treated as a larger integrated circuit. We’ll be discussing the various aspects of MCM packaging, including recent trends, key technologies, and the advantages it offers in terms of power efficiency, reliability, streamlined design, and cost-effectiveness.

What is MCM Packaging 

An MCM is an electronic assembly that incorporates multiple ICs or "chips," semiconductor dies, and/or other discrete components. It typically consists of a package with several conductor terminals or "pins" and is integrated onto a unifying substrate. When in use, the MCM can be treated as if it were a larger IC. Alternative terms for MCM packaging include "heterogeneous integration" or "hybrid integrated circuit."

MCM packaging can vary in complexity, ranging from the utilization of pre-packaged ICs on a small printed circuit board (PCB) designed to mimic the footprint of an existing chip package, to the creation of fully customized chip packages that integrate numerous chip dies on a high-density interconnection (HDI) substrate. 

Modern-day Trends in MCM Packaging 

The interconnecting substrate that links the ICs in an MCM is referred to as an interposer. Interposers can be made either of organic materials, like laminated circuit boards containing carbon or silicon, as seen in high-bandwidth memory (HBM) discussed below. Each option has its own advantages and limitations. Utilizing interposers to connect multiple ICs instead of separate monolithic ICs reduces power consumption for signal transmission, increases the number of transmission channels, and minimizes delays caused by resistance/capacitance (RC delays). However, communication between chiplets in this configuration requires more power and has higher latency compared to components within monolithic ICs.

There are four notable recent MCM packaging technologies:

1. Organic Substrate: This 2D standard packaging type is cost-effective and widely used in the semiconductor industry, particularly for applications with lower IO density and fewer die-to-die connections. It has higher yields due to the absence of delicate microbumps present in other packaging types. In this configuration, each die is connected to a substrate, and the MCM connects to the larger board oftentimes through a BGA.

2. Redistribution Layer (RDL) Fan-Out: These relatively new packages provide similar density to silicon interposers but at a lower cost and complexity. These 2.5D advanced MCM RDL fan-out packages assemble one or more dies, resulting in improved performance and increased IOs suitable for IoT, networking, and computing applications.

3. Silicon Interposer: In this 2.5D packaging type, a silicon-based interposer connects two dies. Microbumps enable dense connectivity using a vertical interconnect technology for stacked dies. The complex assembly and delicate nature of microbumps pose challenges in terms of yields, but packaging vendors address this through quality assurance measures and test and repair mechanisms. 

4. Hybrid Bonding: This 3D stacked packaging approach offers the highest density and power efficiency. It involves bonding two wafers together, working as a single unit, with through-silicon vias (TSVs) for connectivity. Hybrid bonding minimizes power wastage when driving channels, and the power of each IO can be reduced as needed. However, it presents greater complexity and cost compared to interposers. This is also known as a chip-stack "chip-stack" package. Certain ICs, memories in particular, have very similar or identical pinouts when used multiple times within systems. A carefully designed substrate can allow these dies to be stacked in a vertical configuration making the resultant MCM's footprint much smaller (albeit at the cost of a thicker or taller chip). 

Especially through this fourth MCM packaging type, the intracacies of die-to-die connectivity are worth mentioning—facilitating communication between two or more dies within a package. The interface for die-to-die communication needs to be optimized for the specific characteristics of each package type. For example, interposers are not designed to support high-speed communication between channels, so high-speed die-to-die interface IP can be employed. 

MCM Advantages

MCMs offer several advantages:

1. Power Efficiency: MCMs consume less power compared to systems with separate electronic components. Since all the necessary components are integrated onto the same assembly, the length of interconnections is significantly reduced. This shorter interconnection length leads to lower power requirements.

2. Enhanced Reliability: With multiple chips on a single PCB board, MCM packages contain fewer interconnections between components. This reduction in interconnections means there are fewer points of failure for the assembly, resulting in improved reliability.

3. Streamlined Design: PCB boards incorporating MCMs can support multiple functions, enabling the creation of flexible electronic devices capable of accommodating various functions and technologies. The simplified design also facilitates faster manufacturing and time-to-market for these devices.

4. Cost-effectiveness: The aforementioned advantages of MCMs, such as reduced power consumption, improved reliability, and simplified design, contribute to lower production costs. By combining these features, MCMs offer a cost-effective solution for electronic assemblies.

As the demand for advanced MCM packaging continues to grow, it becomes essential to have the right tools at your disposal. Allegro X Advanced Package Designer is a comprehensive software solution designed for MCM packaging design and optimization. Don't miss out on the opportunity to unlock the full potential of your MCM packaging design.