Recessed Circuit Board Pad Structure for Stronger Solder Bonding
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Solution Overview
Problem
Conventional semiconductor packages face issues with reduced adhesion and bonding strength between pads and solder bumps due to decreased pad sizes, leading to physical and electrical reliability problems.
Innovation Solution
A circuit board and semiconductor package design featuring a pad with a recess and a protective layer having an opening overlapping the pad, where the connecting member fills the recess and opening, enhancing adhesion and bonding strength through an anchor structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pad size is reduced for miniaturization and integration, then the integration of the semiconductor package is improved, but the contact area between the pad and solder bump is reduced, leading to reduced adhesion
Solution Approach 1:
The invention transitions from a two-dimensional pad surface to a three-dimensional structure by forming a recess (concave portion) in the pad. This vertical dimension allows the solder bump to embed into the pad, increasing the contact area and adhesion strength without requiring a larger pad footprint, thus resolving the contradiction between miniaturization and adhesion reliability
Solution Approach 2:
The solder bump is positioned to fill and embed into the recess formed in the pad, creating a nested structure where the solder bump is partially contained within the pad's concave portion. This nesting increases the bonding interface area and mechanical interlocking, improving adhesion while maintaining compact dimensions
2Productivity
If the pad size is reduced for integration, then the integration density is improved, but the bonding strength between pad and connecting member is reduced
Solution Approach 1:
By introducing a vertical recess in the pad structure, the invention exploits the third dimension to increase bonding strength. The recess allows deeper embedding of the connecting member, providing enhanced mechanical interlocking and bonding strength without increasing the horizontal pad dimensions, thus maintaining high integration density
Solution Approach 2:
The pad structure combines multiple material layers including a copper layer and a barrier layer, forming a composite structure that provides both mechanical strength and electrical conductivity. This composite approach enhances bonding strength while maintaining compact pad dimensions for high integration
3Area of moving object
If the pad size is reduced, then the miniaturization is achieved, but the physical reliability is reduced due to solder bump separation
Solution Approach 1:
The recess structure introduces a vertical dimension that creates mechanical interlocking between the solder bump and pad. This three-dimensional bonding configuration prevents solder bump separation and improves physical reliability, even when the horizontal pad area is reduced for miniaturization
Solution Approach 2:
The recess in the pad provides a curved or concave surface that complements the spherical or dome-shaped solder bump geometry. This geometric compatibility enhances the bonding interface and prevents separation, improving physical reliability in miniaturized packages
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 2c
AI summary
A circuit board according to an embodiment comprises an insulating layer; a circuit pattern layer disposed on the insulating layer and including a pad; and a protective layer disposed on the insulating layer and including an opening vertically overlapping the pad, wherein the pad includes a recess concave from an upper surface of the pad toward a lower surface of the pad, wherein the protective layer includes a first region including the opening and vertically overlapping the pad, and a second region excluding the first region, wherein the pad includes a first portion including the recess; and a second portion connected to the first portion and not having the recess, wherein the first portion of the pad includes a first sub-portion vertically overlapping the opening of the protective layer, and a second sub-portion vertically overlapping a lower surface of the first region of the protective layer, and wherein a width of the second sub-portion of the pad is greater than a width of the second portion of the pad.