PCB Pad Corner Truncation for Solder Joint Stress Relief
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Solution Overview
Problem
Conventional printed wiring boards experience high stress at soldered portions of pads located at the ends of pad rows during temperature cycles, leading to a high likelihood of rupture and failure.
Innovation Solution
The pads at the ends of the pad rows are extended outwardly from the center of the electronic component with a shape obtained by diagonally cutting the corner farthest from the center, providing additional support and increasing the solder area for improved stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional rectangular pads are used at the ends of pad rows, then the structure is simple and easy to manufacture, but the soldered portions experience high stress during temperature cycles leading to rupture and failure
Solution Approach 1:
The pad shape is modified locally at the end portions where stress concentration occurs. Specifically, the outer corners of the end pads are cut off to create a truncated corner configuration, while other pads maintain their conventional rectangular shape. This localized modification redistributes stress away from the vulnerable soldered portions without requiring complex changes throughout the entire pad structure.
Solution Approach 2:
The end pads are designed with asymmetric corner cutting where only the outer corners (farthest from the electronic component center) are removed. This creates an asymmetric geometry that specifically addresses the stress concentration at the outer edges of the pad row, while maintaining symmetry and simplicity for the inner pads that do not experience the same stress levels.
2Reliability
If pad extensions are added to distribute stress, then the rupture life of soldered portions is extended, but the manufacturing process becomes more complex
Solution Approach 1:
Instead of extending all pads uniformly, the corner cutting is applied only to the end pads where stress concentration occurs during temperature cycling. This localized approach provides the stress distribution benefit where needed while minimizing the impact on manufacturing complexity compared to a universal pad extension design.
Solution Approach 2:
The pad geometry parameter is changed by removing material at the outer corners rather than adding extensions. This parameter modification (corner truncation) achieves stress distribution by altering the stress concentration points, and can be implemented through standard PCB fabrication processes such as laser cutting or mechanical routing, maintaining ease of manufacture.
Data Source
AI summary
In a printed wiring board on which an electronic component comprising electrode terminal rows on four peripheral sides or two opposite sides thereof is mounted, each of pads at the both ends of pad rows corresponding to the electrode terminal rows extend outwardly relative to the other pads in the direction of arrangement of the pads and has a shape obtained by diagonally cutting a corner located farthest from the center of the electronic component.