Undercut Solder Joint Structure for Semiconductor Stress Mitigation
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Solution Overview
Problem
Semiconductor packages with reduced solder balls are susceptible to stress-induced cracks due to external forces, as the remaining solder balls concentrate mechanical shock forces, leading to stress concentration points that can cause failures.
Innovation Solution
A solder material receiving curved surface with a solder resist that forms an undercut, distributing forces more evenly across the solder material, reducing stress concentrations and preventing cracks by creating a curved transition instead of orthogonal angles during solder reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the number of solder balls is reduced to achieve smaller package size, then the package size is reduced, but the solder balls become more susceptible to stress-induced cracks under external forces
Solution Approach 1:
The patent applies curvature by forming the solder joint with a curved interface between the solder ball and substrate instead of a sharp orthogonal angle. This curved transition distributes stress more evenly throughout the solder material, preventing stress concentration at corners or edges, thereby improving reliability while maintaining reduced package size
Solution Approach 2:
The patent changes the geometric parameters of the solder joint by creating a specific curved profile with controlled radius of curvature. This parameter modification allows the solder joint to better absorb and distribute mechanical shock forces, enhancing reliability without requiring additional solder balls or increasing package volume
2Adaptability or versatility
If solder balls are concentrated at edges and corners to maintain connectivity, then connectivity is maintained, but stress concentration occurs leading to cracks under gravitational forces
Solution Approach 1:
The curved solder joint profile eliminates sharp angles at the interface between solder and substrate. This curvature redistributes the stress field generated by gravitational forces and mechanical shocks, preventing the formation of stress concentration points that would otherwise lead to crack initiation at edge and corner locations
Data Source
AI summary
A device and substrate are disclosed. An illustrative device includes a substrate having a first surface and an opposing second surface, a solder material receiving curved surface exposed at the second surface of the substrate, a solder resist material that at least partially covers the solder material receiving curved surface such that a middle portion of the solder receiving curved surface is exposed and such that an edge portion of the solder material receiving curved surface is covered by the solder resist material and forms an undercut, and a solder material disposed within the solder material receiving curved surface and within the undercut.