Recessed Circuit Board Contacts for Solder Bonding Reliability
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Solution Overview
Problem
Existing circuit boards face issues with reduced bonding area between solder and bumps, leading to reliability problems, and increased thickness due to protruding metal layers, which affect electrical and physical reliability.
Innovation Solution
The circuit board design incorporates a protective layer with recess portions and a metal layer that extends into these recesses, increasing bonding area without increasing overall thickness, and a surface treatment layer with a thickness of at least 4 μm to improve adhesion and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surface treatment layer or bump is added to improve adhesion to solder, then bonding properties are improved, but the overall thickness of the circuit board increases
Solution Approach 1:
The metal layer is nested within the recess portion of the protective layer, creating a stepped structure where the metal layer is positioned below the upper surface of the protective layer. This nesting approach allows the metal layer to be integrated into the existing structure without adding to the overall thickness, while still providing the necessary bonding surface for solder adhesion.
Solution Approach 2:
The protective layer is designed with different local properties: a recess portion where the metal layer is exposed to provide bonding surface, and an upper surface that remains at the original thickness level. This local differentiation allows the circuit board to maintain overall thickness control while providing enhanced bonding properties at the specific location where solder connection is needed.
2Productivity
If the opening region of solder resist is reduced to improve I/O performance, then density increases, but the bonding area between solder and metal layer decreases
Solution Approach 1:
The metal layer is nested within the recess portion of the protective layer, allowing the bonding surface to extend laterally within the recess area. This enables the bonding area to be increased without increasing the opening region size, as the metal layer utilizes the recess space to provide adequate solder contact area even when the opening region is small.
Solution Approach 2:
The solution transitions from a two-dimensional bonding surface (flat metal layer on surface) to a three-dimensional structure (metal layer within recess portion). By utilizing the vertical dimension to create a recess, the bonding area is expanded laterally within the confined opening region, allowing adequate bonding area to be achieved without increasing the opening size.
Data Source
AI summary
A circuit board according to an embodiment includes an insulating layer; a circuit pattern layer including a first metal layer disposed on the insulating layer; a protective layer disposed on the insulating layer, vertically overlapping the first metal layer, and including a recess portion having a step in a horizontal direction; and a second metal layer disposed in the recess portion of the protective layer, wherein the recess portion includes a portion having a width greater than a width of the first metal layer, and wherein the second metal layer is disposed in the portion of the recess portion with a width greater than the width of the first metal layer.