Flexible Substrate System for IC Package Stacking
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Solution Overview
Problem
The existing integrated circuit packaging technologies face challenges with solder cracking due to differential coefficients of thermal expansion between semiconductor chips and substrates, leading to reduced reliability and manufacturing yield, especially in multichip modules where increased heat dissipation and mechanical stress exacerbate these issues.
Innovation Solution
A flexible substrate system is introduced, comprising an insulating material with stacking and coupling pads and traces, coupled to a package substrate using conductive adhesive, allowing for elastic deformation and improved thermal management, thereby reducing solder cracking and enhancing manufacturing yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder connections are used to interconnect chip contacts to substrate, then electrical connection is achieved, but solder cracking occurs due to differential thermal expansion
Solution Approach 1:
The patent introduces an intermediary compliant layer between the rigid substrate and the chip package. This layer acts as a mediator that absorbs and distributes the thermal expansion stresses, preventing them from concentrating on the solder joints. The compliant layer has mechanical properties that allow it to deform elastically under thermal stress while maintaining electrical connectivity, thus protecting the solder connections from cracking.
Solution Approach 2:
The patent changes the mechanical parameters of the interconnection structure by introducing a compliant layer with specific elastic modulus and thickness. This modifies the overall stiffness of the assembly, allowing it to better accommodate thermal expansion differences. The compliant layer's parameters are optimized to provide sufficient flexibility to absorb thermal stress while maintaining structural integrity and electrical connection.
2Adaptability or versatility
If multiple semiconductor chips are packaged together in multichip modules, then functional integration is improved, but mechanical stress and heat dissipation increase causing greater solder cracking susceptibility
Solution Approach 1:
In multichip module configurations, the compliant layer serves as a critical intermediary between the substrate and multiple chip packages. It distributes the cumulative thermal expansion stresses from multiple chips across a larger area, preventing stress concentration at any single solder joint. The layer's compliance allows it to accommodate the combined thermal loads from multiple heat-generating components.
Solution Approach 2:
The compliant layer provides beforehand cushioning by being pre-positioned between the substrate and chip packages. It is designed with sufficient thickness and compliance to absorb anticipated thermal expansion stresses before they can damage the solder joints. This preventive measure is built into the structure during manufacturing, cushioning against future thermal cycling damage.
3Adaptability or versatility
If the number of integrated circuits in the package increases, then functional capability is improved, but manufacturing yield decreases due to difficulty in achieving good yields
Solution Approach 1:
The patent segments the interconnection structure into distinct functional layers: the rigid substrate, the compliant intermediate layer, and the chip packages. This segmentation allows each layer to be optimized independently for its specific function. The compliant layer can be separately manufactured and tested before assembly, enabling quality control at intermediate stages and improving overall manufacturing yield for complex multichip modules.
4Stability of the object's composition
If solder columns are designed to be short to maintain structural integrity, then structural stability is improved, but elastic solder connection properties are minimized reducing reliability
Solution Approach 1:
The compliant layer acts as an intermediary that compensates for the limited elastic properties of short solder columns. By providing additional compliance at the substrate level, it allows the overall assembly to accommodate thermal expansion even when the solder joints themselves are short and rigid. This separates the structural support function (performed by short, rigid solder columns) from the thermal stress absorption function (performed by the compliant layer).
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The flexible substrate system effectively mitigates thermal expansion issues, improves electrical performance, and simplifies manufacturing by allowing tested components to be assembled, resulting in increased reliability and yield while maintaining compatibility with conventional manufacturing processes.
Implementation Method 1
applying a conductive adhesive on the package substrate for positioning the flexible substrate over the integrated circuit and coupling the flexible substrate on the conductive adhesive
Implementation Method 2
The flexible substrate system effectively mitigates thermal expansion issues... allowing for elastic deformation
Data Source
AI summary
An integrated circuit package stacking system includes: forming a flexible substrate by: providing an insulating material, forming a stacking pad on the insulating material, forming a coupling pad on the insulating material, and forming a trace between the stacking pad and the coupling pad; providing a package substrate; coupling an integrated circuit to the package substrate; and applying a conductive adhesive on the package substrate for positioning the flexible substrate over the integrated circuit and coupling the flexible substrate on the conductive adhesive.