Reliability Cover Mitigates Thermal Expansion Mismatch in BGA Assemblies
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Solution Overview
Problem
Solder joints in ball grid array assemblies between integrated circuit packages and printed circuit boards are prone to failure due to thermal expansion mismatches, leading to cracking and reduced reliability under stress conditions.
Innovation Solution
A reliability cover with a high coefficient of thermal expansion is disposed over the integrated circuit package and Si die to reduce the thermal expansion mismatch between the package, substrate, and printed circuit board, thereby minimizing shear stresses and enhancing solder joint durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder joints are used to connect integrated circuit package to printed circuit board, then electrical interconnection is achieved, but solder joints are prone to cracking under thermal stress
Solution Approach 1:
The patent introduces a reliability cover as an intermediary component disposed between the integrated circuit package and the printed circuit board. This cover has a coefficient of thermal expansion specifically selected to reduce the thermal expansion mismatch between the IC package and PCB, thereby acting as a mediator that minimizes shear stresses on solder joints during thermal cycling
Solution Approach 2:
The patent changes the thermal expansion parameter by selecting a reliability cover material with a specific coefficient of thermal expansion that falls between the IC package and PCB values. This parameter optimization reduces the differential thermal expansion, thereby protecting solder joints from cracking under thermal stress
2Ease of manufacture
If integrated circuit package is mounted directly to printed circuit board, then assembly is simple, but thermal expansion differences cause stress and cracking
Solution Approach 1:
The reliability cover serves as an intermediary layer that maintains assembly simplicity while addressing the thermal expansion mismatch issue. It is disposed between the IC package and PCB, requiring minimal additional manufacturing steps while significantly improving joint strength and reliability under thermal stress
3Adaptability or versatility
If solder joints are exposed to temperature extremes, then functional operation is enabled, but solder joints crack due to repeated thermal cycling
Solution Approach 1:
The reliability cover provides beforehand cushioning by absorbing and distributing the thermal expansion stresses before they reach the solder joints. During repeated thermal cycling, the cover acts as a protective buffer that cushions the solder joints from cracking, enabling the assembly to withstand temperature extremes while maintaining reliability
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 solution effectively reduces solder joint failures by equalizing thermal expansion rates, increasing the robustness of the joints, and improving their ability to withstand temperature extremes and dynamic warpage.
Implementation Method 1
The reliability cover is configured to reduce a difference in a coefficient of thermal expansion between the integrated circuit package and the printed circuit board, and between the Si die and a substrate of the integrated circuit package by a threshold value
Data Source
AI summary
A reliability cover that is disposed over at least one of an integrated circuit package and a Si die of the integrated circuit package is disclosed. The integrated circuit package is mountable to a printed circuit board via a plurality of solder balls. The reliability cover is configured to reduce a difference in a coefficient of thermal expansion between the integrated circuit package and the printed circuit board, and between the Si die and a substrate of the integrated circuit package by a threshold value.