Asymmetric Drum-Shaped Through-Hole for Printed Wiring Board
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Solution Overview
Problem
The existing printed wiring boards face issues with void formation and reduced durability and conductivity due to stress concentration at the fringe portions of through-holes, especially when the diameter is reduced, leading to incomplete metal filling and potential cracking under bending stress.
Innovation Solution
A printed wiring board design with a through-hole that gradually decreases in diameter from the first surface to the second surface, and a metal plated layer with controlled thickness, preventing void formation by ensuring the plating metal fills the hole from the second surface side, reducing stress concentration and enhancing durability and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the through-hole is reduced, then the size of the printed wiring board is reduced, but the opening of the through-hole is closed by the metal plated layer before the metal sufficiently fills the inside of the through-hole, causing void formation
Solution Approach 1:
The through-hole is designed with an asymmetric drum shape where the diameter varies along the thickness direction - larger at the opening and smaller at the center. This asymmetric geometry controls the plating current distribution to prevent fringe portion concentration while ensuring complete filling, resolving the contradiction between reduced hole size and prevention of void formation
Solution Approach 2:
The diameter parameter of the through-hole is changed along its length, creating a tapered drum shape. By making the diameter at the opening larger than at the center, the plating process can accommodate smaller overall dimensions while preventing premature closure and void formation through controlled current distribution
2Manufacturing precision
If the diameter of the through-hole is reduced, then the refinement of wirings is achieved, but stress concentration occurs at the fringe portions, reducing durability and conductivity
Solution Approach 1:
The asymmetric drum-shaped through-hole design with larger opening diameter and smaller center diameter redistributes the stress away from the fringe portions. This geometric asymmetry prevents stress concentration while maintaining refined wiring dimensions, thus improving both manufacturing precision and structural strength
Solution Approach 2:
Different sections of the through-hole are given different diameters - the opening portion has a larger diameter to reduce stress concentration at fringe portions, while the center portion has a smaller diameter to achieve wiring refinement. This local variation in geometry simultaneously achieves both objectives
3Reliability
If the through-hole is formed with a drum shape to prevent void formation, then the plating metal fills the hole successfully, but the manufacturing complexity increases
Solution Approach 1:
The drum shape of the through-hole is pre-formed in the insulator before the plating process. This preliminary geometric preparation ensures that during electroplating, the current distributes evenly and the metal fills the hole completely without voids, while avoiding the need for complex post-plating corrections
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 effectively prevents void formation and reduces stress concentration, thereby improving the durability and conductivity of the printed wiring board while ensuring complete metal filling of the through-hole.
Implementation Method 1
Generally, the through-hole is formed by performing an electroless plating on an inner peripheral surface of the through-hole formed in a base insulator
Implementation Method 2
performing electroplating on an adherend, electroless plated layer that is formed by the electroless plating
Data Source
AI summary
A printed wiring board includes an insulator having a first surface, and a second surface opposite to the first surface, a through-hole penetrating from the first surface to the second surface, and a metal plated layer formed on the first and second surfaces of the insulator, and on an inner peripheral surface of the through-hole, wherein an inside diameter of the through-hole gradually decreases from the first surface toward the second surface of the insulator. An average diameter of the through-hole is 20 μm or greater and 35 μm or less at the first surface, and is 3 μm or greater and 15 μm or less at the second surface, and an average thickness of the metal plated layer formed on the first and second surfaces is 8 μm or greater and 12 μm or less.