Via Filling in Printed Wiring Boards Using O2 Plasma Desmearing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for manufacturing printed wiring boards face challenges with desmearing and filling via drill holes, especially when using materials like PTFE with high water absorption and forming vias of large diameters or deep depths, leading to incomplete smear removal and insufficient filling due to issues with laser beam strength and plating deposition.
Innovation Solution
The method involves forming a conical frustum-shaped via drill hole with a conductive material, using a dry desmearing process like O2 plasma processing, and a two-step filling process to ensure complete smear removal and sufficient filling, even with constraints on material and size, using a copper-clad laminate and electrolytic plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a laser beam is used to form a via drill hole in a resin layer, then the hole can be formed through the insulating layer, but residual smear (resin residue) remains in the hole preventing complete filling
Solution Approach 1:
The patent applies preliminary action by performing O2 plasma treatment on the inner surface of the via drill hole before filling it with conductive material. This preliminary cleaning action removes resin smear residues that would otherwise prevent complete filling, ensuring the hole surface is properly prepared for subsequent electrolytic plating and filling operations.
2Object-generated harmful factors
If the laser beam strength is increased to remove smear, then smear removal improves, but the insulating layer material like PTFE with high water absorption causes incomplete smear removal and filling issues
Solution Approach 1:
The patent changes the parameter of smear removal method from mechanical/thermal (laser) to chemical/physical (O2 plasma). This parameter change allows effective smear removal without relying on increasing laser strength, thereby avoiding damage to PTFE insulating layer materials with high water absorption and ensuring reliable via filling.
Solution Approach 2:
The patent substitutes the mechanical/thermal laser beam system with a plasma-based chemical cleaning system. This replacement enables effective smear removal through O2 plasma oxidation without the harmful effects of high-intensity laser on water-absorbing insulating materials, improving both smear removal efficiency and filling reliability.
3Quantity of substance
If electrolytic plating is used to form a wiring layer in the via drill hole, then conductive material is deposited, but residual smear prevents complete filling and compromises conduction performance
Solution Approach 1:
The patent applies preliminary O2 plasma treatment to the via drill hole inner surface before electrolytic plating. This preliminary action removes residual smear that would interfere with conductive material deposition, ensuring complete filling and reliable conduction performance by creating a clean surface for uniform plating.
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
This approach allows for the formation of vias without residual smear and ensures complete filling, preventing water absorption issues with PTFE and enhancing the reliability of conduction performance, especially for large-diameter or deep vias.
Implementation Method 1
using a dry desmearing process like O2 plasma processing
Implementation Method 2
O2 plasma processing
Implementation Method 3
using a copper-clad laminate and electrolytic plating
Data Source
AI summary
Forming, in a printed-wiring board, a via sufficiently filled without residual smear, for use in an insulating layer and the size of the via to be formed. A via of a printed-wiring board comprises a first filling portion which fills at least a center portion of a hole, and a second filling portion which fills a region of the hole that is not filled with the first filling portion. An interface which exists between the second and first filling portions, or an interface which exists between the second filling portion and an insulating layer and the first filling portion has the shape of a truncated cone comprising a tapered surface which is inclined to become thinner from a first surface toward a second surface, and an upper base surface which is positioned in parallel to the second surface and closer to the first surface than to the second surface.