Wiring Board Recessed Pad Surface Roughness Control
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Solution Overview
Problem
In the manufacturing process of build-up wiring boards, the roughened surface of the support body is transferred to pads, leading to reduced solder wettability and reliability of connections between the pads and semiconductor chip electrodes.
Innovation Solution
A wiring board design featuring an insulating layer with recessed pads and a solder resist layer, where the pads have smooth and roughened surfaces to enhance adhesion and solder wettability, and the solder resist layer covers the pads to prevent peeling and ensure reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the support body surface is roughened to improve adhesion of insulating layer and solder resist layer, then adhesion property is improved, but the pad surface becomes roughened which reduces solder wettability
Solution Approach 1:
The patent applies different surface roughness characteristics to different regions: the insulating layer surface is roughened to improve adhesion, while the pad surface is kept smooth to maintain solder wettability. This local differentiation resolves the contradiction by ensuring each region has the surface properties needed for its specific function.
Solution Approach 2:
The patent segments the surface into distinct functional zones: a roughened insulating layer surface for adhesion and a smooth pad surface for soldering. This segmentation allows independent optimization of each zone's surface properties without compromise.
2Reliability
If the pad surface is kept smooth to maintain solder wettability, then solder wettability is improved, but adhesion property between insulating layer and pad is reduced
Solution Approach 1:
The pad structure incorporates a recessed portion with a smooth bottom surface for solder wettability, while the surrounding insulating layer surface is roughened for adhesion. This local quality differentiation allows the pad to achieve both smooth soldering surface and good adhesion through the roughened surrounding area.
Solution Approach 2:
The smooth pad surface is nested within a roughened insulating layer environment. The recessed pad structure is embedded in the roughened insulating layer, creating a nested configuration where the smooth pad area provides soldering functionality while the roughened surrounding layer provides adhesion functionality.
3Strength
If the solder resist layer is formed on the roughened pad surface, then adhesion is improved, but the roughness causes uneven solder distribution and reduced reliability
Solution Approach 1:
The solder resist layer is formed only on the smooth surfaces where needed (the bottom of the recessed pad portion and the insulating layer surface away from the pad), while avoiding the pad top surface. This local quality approach ensures uniform solder distribution on smooth surfaces while maintaining adhesion where required.
Data Source
AI summary
A wiring substrate includes an insulating layer, a pad, and a solder resist layer. The insulating layer has a first surface formed with a first recess portion. The pad is embedded in the first recess portion. The pad includes a second surface and a third surface. The third surface that is located at a lower position than the first surface so as to expose an inner wall surface of the first recess portion. The pad is formed with a second recess portion in a center portion of the third surface. The solder resist layer is provided on the first surface. An adjacent portion of the first surface to a peripheral portion of the first recess portion is smaller in roughness than a region of the first surface peripheral to the adjacent portion of the first surface.