Wiring Board Notch Electrode Composition for Solder Peeling
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Solution Overview
Problem
The precision of wiring boards has increased, leading to reduced adhesiveness of inner-face electrodes formed on insulating bases, which can result in peeling off due to thermal expansion stress when bonded to module boards with solder.
Innovation Solution
A wiring board with an insulating base and a notch portion, where the inner-face electrode contains nickel and gold, with more nickel at the surface periphery and more gold in the inner region, preventing solder adhesion and stress-induced peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the inner-face electrode is formed through the thin film method to achieve high precision, then the manufacturing precision is improved, but the adhesiveness of the inner-face electrode deteriorates
Solution Approach 1:
The patent applies local quality by creating different metal compositions at different locations of the inner-face electrode surface. The outer periphery section contains more nickel than gold to prevent solder adhesion, while the inner region contains more gold than nickel to ensure proper soldering. This spatial variation in material composition resolves the contradiction by allowing the electrode to have both high precision (from thin film formation) and reliable adhesiveness (through localized material optimization).
Solution Approach 2:
The patent uses composite materials by combining nickel and gold in a specific spatial distribution within the inner-face electrode. The multi-layer or gradient structure with different metal ratios at different locations creates a composite material system that simultaneously achieves high manufacturing precision through thin film techniques and reliable mechanical/adhesive properties through the synergistic combination of nickel's structural stability and gold's solder compatibility.
2Reliability
If solder is applied to bond the inner-face electrode to the module board, then the electrical connection is established, but thermal expansion stress causes the inner-face electrode to peel off
Solution Approach 1:
The patent applies local quality by creating different metal compositions at different locations of the inner-face electrode surface. The outer periphery section contains more nickel than gold to prevent solder adhesion, while the inner region contains more gold than nickel to ensure proper soldering. This spatial variation in material composition resolves the contradiction by allowing the electrode to have both high precision (from thin film formation) and reliable adhesiveness (through localized material optimization).
Solution Approach 2:
The patent converts the harmful effect of thermal expansion stress into a beneficial outcome by using the differential metal composition to manage stress distribution. The nickel-rich outer periphery acts as a stress-resistant zone that prevents solder adhesion and thus eliminates the transmission of thermal expansion stress to the bonding interface, while the gold-rich inner region maintains electrical conductivity. This transforms the potential harm of thermal stress into a protective mechanism.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
A wiring board (1) according to the present invention includes: an insulating base (11) including a main face, a side face, and a notch portion (12) opened in the main face and the side face; and an inner-face electrode (13) disposed on the inner face of the notch portion (12) and to be connected to an external circuit board (5a) with solder (6) therebetween. In such a wiring board (1), the inner-face electrode (13) contains nickel and gold at a surface portion thereof, more nickel than gold at a surface in an outer periphery section (13a), and more gold than nickel at a surface in an inner region.