Circuit Board Conductor Surface Roughness for Solder Adhesion
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Solution Overview
Problem
The smooth surface of circuit boards processed using CMP techniques results in reduced solder adhesion to pad sections, leading to poor connections and reliability issues in semiconductor devices.
Innovation Solution
A circuit board design where the surface roughness of the conductor in the pad section is greater than in the wiring section, with specific ratios and patterns of fine recesses, to enhance solder adhesion and component mountability, while maintaining signal transmission stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If CMP processing is used to polish the circuit board surface, then the surface becomes smooth and planarized, but the adhesion of solder to the pad section is reduced
Solution Approach 1:
The patent applies different surface roughness characteristics to different functional areas of the conductor. The pad section is designed with greater surface roughness to enhance solder adhesion, while the wiring section maintains smaller surface roughness for stable signal transmission. This local differentiation resolves the contradiction by optimizing each area for its specific function rather than applying uniform polishing across the entire surface.
2Reliability
If the surface roughness of the conductor in the pad section is increased to improve solder adhesion, then component mountability is improved, but the flowability of resin sealant is reduced
Solution Approach 1:
The patent confines the increased surface roughness specifically to the pad section where solder adhesion is critical, while keeping the wiring section smooth. This localized approach ensures that the resin sealant's flowability is not significantly impacted, as the rough surface area is limited to discrete pad regions rather than covering the entire circuit board surface.
3Reliability
If the surface roughness of the conductor in the wiring section is increased, then solder adhesion is improved, but the cross-sectional area uniformity and signal transmission stability are reduced
Solution Approach 1:
The patent maintains smooth surfaces in the wiring section to preserve uniform cross-sectional area and stable signal transmission characteristics. Surface roughness is applied only in the pad sections where it is needed for solder adhesion, thus avoiding any negative impact on signal integrity while still achieving reliable component mounting.
Data Source
AI summary
A circuit board includes an electric circuit having a wiring section and a pad section in the surface of an insulating base substrate. The electric circuit is configured such that a conductor is embedded in a circuit recess formed in the surface of the insulating base substrate, and the surface roughness of the conductor is different in the wiring section and the pad section of the electric circuit. In this case, it is preferable that the surface roughness of the conductor in the pad section is greater than the surface roughness of the conductor in the wiring section.