BGA Package Structure Using Underfill and Mixed Balls for Bond Reliability
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Solution Overview
Problem
Ball bond breakage in ball grid arrays (BGAs) during the packaging process, particularly with copper-based balls, leads to reliability issues such as higher electrical resistance and loss of connectivity, especially in miniaturized electronics, where the prevalence of breakage is exacerbated by thermal cycling and increased ball density.
Innovation Solution
The use of an underfill material, such as liquid epoxy or plastic molding compound, is applied around the bonds between electrically conductive balls and substrate or IC chip bonding pads, which is cured before attachment, providing structural reinforcement and preventing electrical contact hindrance. Additionally, employing a combination of copper-based and solder balls in the BGA, with solder balls in peripheral regions to mitigate stress and enhance robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper-based balls are used in BGA to reduce electrical resistance, then electrical conductivity is improved, but ball bond breakage increases during packaging process
Solution Approach 1:
The patent uses a composite ball structure with a copper core providing high electrical conductivity and a solder coating layer providing mechanical strength and bond reliability. This composite material approach allows the ball to simultaneously achieve low electrical resistance from the copper core and high bond strength from the solder coating, resolving the contradiction between conductivity and bond strength
Solution Approach 2:
The patent modifies the ball material composition by creating a layered structure with different material properties - the copper core maintains electrical conductivity while the outer solder coating enhances mechanical properties. This parameter change in material composition allows simultaneous optimization of both electrical and mechanical performance
2Volume of moving object
If ball density is increased to achieve miniaturization, then device size is reduced, but ball bond breakage prevalence increases
Solution Approach 1:
The enhanced ball structure with copper core and solder coating provides superior mechanical strength that enables higher ball density packaging. The improved bond strength from the composite material allows more balls to be packed in smaller areas without proportionally increasing breakage rates
Solution Approach 2:
The solder coating on the copper balls provides a protective layer that cushions against mechanical stresses and thermal cycling effects before damage can occur to the underlying copper structure, thereby maintaining reliability even at higher densities
3Strength
If underfill material is applied around ball bonds, then structural integrity is improved, but electrical contact may be hindered
Solution Approach 1:
The underfill material is applied locally around the ball bonds rather than covering the entire ball surface. This localized application provides structural reinforcement at the critical bond interface while leaving the electrical contact surfaces of the balls exposed and functional
Solution Approach 2:
The ball surface is effectively segmented into different functional zones - the portion covered by underfill provides mechanical support while the exposed portions maintain electrical connectivity. This spatial segmentation allows simultaneous achievement of structural integrity and electrical contact
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 underfill material enhances the structural integrity of ball bonds, reducing the likelihood of breakage and maintaining electrical connectivity, while the mixed ball types improve reliability by distributing stress and maintaining high conductivity where needed.
Implementation Method 1
an underfill material, such as liquid epoxy or plastic molding compound, is applied around the bonds between electrically conductive balls and substrate or IC chip bonding pads, which is cured before attachment
Data Source
AI summary
A substrate or IC chip is connected with a second substrate or IC chip. This entails disposing electrically conductive balls on electrical bonding pads of a surface of the substrate or IC chip to form a ball grid array (BGA) disposed on the surface of the substrate or IC chip, and electrically and mechanically connecting the surface of the substrate or IC chip to the second substrate or IC chip using the BGA. An underfill material may be disposed on the surface of the substrate or IC chip around bonds between the balls and the electrical bonding pads. There may be at least two different types of electrically conductive balls in the BGA, such as solder balls and copper-based balls.