Circuit Board Dam Corner Geometry for Void-Free Underfill
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Solution Overview
Problem
Conventional dam members with right-angle or acute-angle inner wall surfaces in corner parts of the dam member lead to insufficient underfill coverage, resulting in voids and potential cracks due to thermal expansion.
Innovation Solution
A dam member with a rectangular frame design featuring a slope on the inner wall surface of the corner parts and a receding part on the outer wall surface, allowing the underfill to reach the corners and providing a sufficient anchor effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the inner wall surface of the corner part of the dam member is set at a right angle or acute angle, then the dam member structure is simple, but the underfill does not reach the corner parts sufficiently and voids occur
Solution Approach 1:
The patent applies curvature by forming a rounded corner part instead of a sharp right angle or acute angle. This curved geometry allows the underfill to flow smoothly into the corner region, eliminating voids while maintaining structural simplicity. The rounded shape guides the underfill material to reach all corner surfaces effectively.
Solution Approach 2:
The patent applies different geometric characteristics to different parts of the dam member. Specifically, the corner parts are designed with a rounded shape that differs from the straight lines of the main dam body. This local differentiation ensures that the underfill can properly penetrate and bond with the corner surfaces, improving coverage without complicating the overall structure.
2Ease of manufacture
If the inner wall surface of the corner part is set at a right angle or acute angle, then the dam member is easy to manufacture, but voids remain due to the shape effect
Solution Approach 1:
The rounded corner design maintains ease of manufacture while significantly improving reliability. The curved geometry is straightforward to form during standard dam member fabrication processes, yet it effectively guides the underfill to reach all corner surfaces, eliminating voids and ensuring reliable bonding.
3Productivity
If voids occur in the underfill, then the underfill can be easily poured, but thermal expansion causes cracks near the solder resist layer or dam member
Solution Approach 1:
The rounded corner geometry prevents void formation while maintaining smooth underfill flow. By eliminating air pockets and ensuring complete underfill coverage, the structure gains crack resistance through improved thermal expansion uniformity, without compromising pouring efficiency.
Data Source
AI summary
A circuit board includes an insulating layer that is layered on a substrate; and a dam member in a form of a rectangular frame that is formed on the insulating layer. A corner part of the dam member includes a slope that slopes down from an inner wall surface to a surface of the insulating layer in a lower part that makes contact with the surface of the insulating layer; and a perpendicular part that is perpendicular to the surface of the insulating layer in an upper part separated from the surface of the insulating layer.