Conductor Post Surface Roughness for PCB Adhesion and Solderability
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Solution Overview
Problem
Existing printed wiring boards face challenges in achieving optimal adhesion between the resin insulating layer and conductor posts due to differences in thermal expansion coefficients, leading to peeling issues, and in ensuring stable connections for semiconductor chips and motherboards due to excessive surface roughness affecting solderability and electrical characteristics.
Innovation Solution
A printed wiring board design featuring a wiring conductor layer with a resin insulating layer and conductor posts, where the side surface of the conductor post has a higher surface roughness (R1) than the end surface (R2), with R1 > R2, to enhance adhesion and a method involving roughening treatments and etching to achieve these surface roughness values, ensuring stable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the conductor post side surface is roughened to improve adhesion with the resin insulating layer, then adhesion strength is improved, but the end surface roughness increases which deteriorates solderability
Solution Approach 1:
The conductor post is designed with different surface roughness characteristics at different locations: the side surface has higher roughness (first roughness) to enhance adhesion with the resin insulating layer, while the end surface has lower roughness (second roughness) to ensure good solderability. This local differentiation of surface properties resolves the contradiction between adhesion strength and solderability.
Solution Approach 2:
The surface roughening treatment is applied to the conductor post before the resin insulating layer is formed. This preliminary roughening of the side surface ensures optimal adhesion from the beginning, while the end surface roughness is controlled to remain suitable for subsequent soldering operations.
2Strength
If the conductor post end surface is roughened to improve adhesion, then adhesion is improved, but contact resistance increases due to excessive roughness
Solution Approach 1:
Different surface roughness levels are applied to different parts of the conductor post: the side surface has higher roughness for adhesion, while the end surface has controlled, lower roughness to minimize contact resistance and ensure stable electrical connections.
3Ease of manufacture
If uniform surface roughness is applied to the entire conductor post, then manufacturing process is simplified, but both adhesion and solderability cannot be optimized simultaneously
Solution Approach 1:
The conductor post features location-specific surface roughness: the side surface is roughened for adhesion with the resin insulating layer, while the end surface maintains lower roughness for solderability. This local differentiation optimizes both adhesion and electrical connection quality simultaneously.
Solution Approach 2:
The side surface roughening is performed as a preliminary treatment before resin application, ensuring adhesion is established early in the manufacturing process, while the end surface roughness is controlled to preserve solderability for later stages.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design improves adhesion between the resin insulating layer and conductor posts, reduces peeling, and enhances solderability and electrical characteristics by allowing easier solder penetration and increased contact area, thereby stabilizing connections.
Implementation Method 1
the side surface of the conductor post is a roughened side surface having a surface roughness of a first roughness R1
Implementation Method 2
enhances adhesion between the conductor post and resin insulating layer
Implementation Method 3
the end surface of the conductor post is a roughened end surface having a surface roughness of a second roughness R2... R1>R2... ensures stable electrical connections with reduced contact resistance by optimizing surface roughness for improved solderability
Data Source
AI summary
A printed wiring board includes a resin insulating layer, a wiring conductor layer embedded in the insulating layer such that the wiring layer has first surface exposed from the insulating layer, and a conductor post formed in the insulating layer and on second surface of the wiring layer on the opposite side with respect to the first surface of the wiring layer such that the conductor post has side surface covered by the insulating layer and end surface exposed from the insulating layer on the opposite side with respect to the wiring layer. The conductor post is formed such that the side surface of the conductor post is a roughened side surface having surface roughness of first roughness R1, the end surface of the conductor post is a roughened end surface having surface roughness of second roughness R2, and the first and second roughnesses R1, R2 satisfy R1>R2.