PCB Through-Hole Conductor Stress Distribution
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Solution Overview
Problem
Existing printed wiring boards with through-hole conductors face challenges in achieving reliable connections and preventing cracking due to uneven stress distribution and voids within the plated layers, particularly when the electrolytic plated film thickness varies significantly from the center to the edge of the penetrating hole.
Innovation Solution
A printed wiring board design featuring a seed layer on the inner wall of the penetrating hole, a laminated electrolytic plated layer with multiple films of varying thickness, and a filled electrolytic plated layer that closes the center portion and fills recessed portions at the ends, mitigating stress concentration and reducing the likelihood of cracking by ensuring a gradual slope and finer particle diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrolytic plating is performed to form a through-hole conductor, then the connection between conductive layers is improved, but stress concentration and cracking occur due to uneven plating thickness from center to edge
Solution Approach 1:
The electrolytic plated layer is divided into multiple segments (first electrolytic plated layer, second electrolytic plated layer, and filled electrolytic plated layer) with different thickness distributions. Each segment addresses specific stress issues: the first layer provides base conductivity, the second layer reinforces the center, and the filled layer addresses edge voids, collectively preventing cracking while maintaining connection reliability
Solution Approach 2:
Different regions of the plated layer are given different thickness qualities to match local stress requirements. The center portion receives thicker plating (second electrolytic plated layer) to withstand higher stress concentration, while the edge portions receive filled plating to eliminate voids and reduce stress peaks, creating a non-uniform but optimally distributed thickness profile
2Strength
If the electrolytic plated layer is made thicker to prevent cracking, then strength is improved, but voids form within the plated structure
Solution Approach 1:
The first electrolytic plated layer is formed as a preliminary structure before adding the second electrolytic plated layer. This preliminary layer provides a foundation that controls initial plating uniformity, preventing void formation early in the process, while allowing subsequent layers to be added with controlled thickness to achieve the desired strength without creating defects
Solution Approach 2:
The filled electrolytic plated layer is applied selectively to specific regions (edge portions) where voids are most likely to form, rather than uniformly across the entire structure. This partial action targets the problem areas with additional material to eliminate voids and reinforce stress-prone regions without unnecessarily increasing overall plating thickness that could cause other defects
3Strength
If multiple electrolytic plated layers are laminated to distribute stress, then crack resistance is improved, but the manufacturing process becomes more complex
Solution Approach 1:
Each electrolytic plated layer serves multiple functions simultaneously: the first layer provides base conductivity and initial stress distribution, the second layer reinforces the center region and adds conductivity, and the filled layer eliminates edge voids and provides additional stress relief. This multi-functionality of each layer reduces the need for additional separate process steps, balancing complexity with performance
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 solution enhances the connection reliability and prevents cracking by distributing stress along the interfaces of the electrolytic plated films, maintaining high reliability even under significant voltage or current applications, and reducing the occurrence of voids within the through-hole conductor.
Implementation Method 1
a laminated electrolytic plated layer formed on the seed layer and a filled electrolytic plated layer formed on the laminated electrolytic plated layer
Data Source
AI summary
A printed wiring board includes an insulative resin substrate having a penetrating hole, a first conductive layer formed on first surface of the substrate, a second conductive layer formed on second surface of the substrate, and a through-hole conductor formed in the hole such that the conductor is connecting the first and second conductive layers. The conductor has a seed layer on inner wall of the hole, a laminated plated layer on the seed layer and a filled plated layer on the laminated layer, the laminated layer is formed such that the laminated layer is closing center portion of the hole and forming recess at end of the hole, the filled layer is formed such that the filled layer is filling the recess, and the laminated layer includes multiple electrolytic plated films laminated along the seed layer and each having thickness which is less at edge than at center.