Stepped Recess Circuit Board for IMC Crack Resistance
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Solution Overview
Problem
The existing circuit boards face reliability issues due to cracks in the metal contact layer (IMC) caused by molding material injection pressure, leading to separation of chips or main boards from the circuit board.
Innovation Solution
A circuit board design with a protective layer featuring a recess portion having a stepped structure, including a first part with a narrower width and a second part with a wider width, and a surface treatment layer on the pad, which increases the inner wall length without increasing the thickness, enhancing the metal contact layer's stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a recess portion is provided in the protective layer for mounting solder balls, then chip mounting and coupling to main board is enabled, but molding material injection pressure is transmitted to the metal contact layer causing cracks and separation
Solution Approach 1:
The recess portion is designed with a stepped structure having different width levels (first width and second width greater than the first width), transforming a simple single-depth recess into a multi-level dimensional structure. This stepped configuration increases the inner wall surface area and length, providing better stress distribution and protection against molding material injection pressure while maintaining chip mounting functionality
Solution Approach 2:
The recess portion is divided into multiple segments with different widths (first part with first width, second part with second width), creating distinct functional zones. The narrower first part provides structural support while the wider second part offers stress absorption space, segmenting the stress distribution and preventing crack propagation through the metal contact layer
2Strength
If the protective layer thickness is increased to protect the metal contact layer, then stress resistance is improved, but the overall circuit board thickness and complexity increase
Solution Approach 1:
Instead of simply increasing the protective layer thickness uniformly, the invention introduces a stepped structure with varying widths at different depth levels. This creates additional horizontal dimensions (first width and second width) within the vertical recess structure, providing enhanced stress resistance through increased inner wall surface area without proportionally increasing overall thickness or structural complexity
Data Source
AI summary
A circuit board according to an embodiment includes an insulating layer; a pad disposed on the insulating layer; and a protective layer disposed on the insulating layer and including a recess portion vertically overlapping with the pad, wherein the protective layer includes a first portion including a first part of the recess portion; and a second portion disposed on the first portion and including a second part of the recess portion connected to the first portion, and wherein a width of the second part of the recess portion is greater than a width of the first part of the recess portion.