Silver Seed Layer Etching for Fine-Pitch Printed Wiring Boards
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Solution Overview
Problem
Existing methods for producing printed wiring boards face challenges such as poor adhesion between the substrate and conductor circuit, undercuts, and non-rectangular cross-sectional shapes, often requiring surface roughening, alkali treatment, or expensive vacuum equipment.
Innovation Solution
A method involving the formation of a conductive metal layer with silver particles on an insulating substrate, followed by electrolytic copper plating and selective removal of the metal layer using a carboxylic acid and hydrogen peroxide etchant, without surface roughening or vacuum equipment, to achieve strong adhesion and rectangular cross-sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If surface roughening is performed to improve adhesion between substrate and plating film, then adhesion strength is improved, but fine-pitch wiring formation becomes difficult and transmission characteristics are degraded
Solution Approach 1:
The invention changes the chemical composition parameters of the etchant by using a mixed solution of ammonium persulfate and hydrogen peroxide instead of traditional single-component etchants. This parameter change enables effective adhesion promotion without requiring surface roughening, thereby avoiding the degradation of fine-pitch wiring formation capability
Solution Approach 2:
The invention replaces the mechanical/physical roughening process with a chemical treatment process using the ammonium persulfate-hydrogen peroxide mixed etchant. This substitution eliminates the need for physical surface modification while achieving the same adhesion promotion effect through chemical interaction
2Reliability
If additional etching is performed to prevent short circuits and improve insulation reliability, then insulation reliability is improved, but wiring width is reduced due to etchant penetration below resist
Solution Approach 1:
The invention changes the etching parameters by using a controlled mixed etchant solution of ammonium persulfate and hydrogen peroxide with specific concentration ratios. This enables precise control of etching depth and rate, achieving adequate insulation reliability while preventing excessive etching that would reduce wiring width
Solution Approach 2:
The etching process uses the mixed etchant solution with controlled parameters that provide feedback control over the etching rate and depth. This allows the process to stop at the appropriate point to maintain wiring dimensions while ensuring insulation reliability
3Ease of manufacture
If subtractive etching process is used to form circuit wiring, then wiring formation is achieved, but copper residue remains in skirting area causing short circuits
Solution Approach 1:
The invention changes the chemical parameters of the etching process by using ammonium persulfate and hydrogen peroxide mixed solution instead of traditional etchants. This parameter change enables complete removal of copper residue in skirting areas while maintaining wiring formation capability, thereby preventing short circuits
Solution Approach 2:
The invention uses a disposable resist material that can be completely removed after serving its purpose as an etching mask. The resist is designed to be easily removable after the etching process, leaving no residue that would cause short circuits
4Strength
If electroless nickel plating is used to form seed layer on polyimide film, then adhesion is achieved through altered layer, but surface structure becomes physically and chemically weak
Solution Approach 1:
The invention changes the chemical composition of the etchant by using ammonium persulfate and hydrogen peroxide mixed solution that selectively removes the altered layer without damaging the underlying polyimide surface. This parameter change enables adhesion promotion while preserving surface structure integrity
Solution Approach 2:
The invention extracts and removes only the weakened altered layer containing open imide rings using the selective etchant, while leaving the intact polyimide surface structure. This extraction eliminates the weak surface structure while maintaining adhesion through the controlled removal process
5Manufacturing precision
If sputtering is used to form electrically conductive seed layer, then no surface roughening is required, but expensive vacuum equipment and complicated process are needed
Solution Approach 1:
The invention replaces the vacuum-based sputtering mechanical process with a chemical wet etching process using ammonium persulfate and hydrogen peroxide mixed solution. This substitution eliminates the need for expensive vacuum equipment while achieving comparable seed layer formation quality
Solution Approach 2:
The invention uses simple, inexpensive chemical etchants (ammonium persulfate and hydrogen peroxide) that can be easily prepared and disposed of, replacing the expensive and complex vacuum equipment required for sputtering. The chemical process is simpler and more cost-effective for seed layer formation
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 method enables high-density, high-performance printed wiring boards with improved adhesion and rectangular cross-sections, suitable for various substrates and applications, at a lower cost.
Implementation Method 1
the etchant contains a carboxylic acid and hydrogen peroxide as active ingredients
Implementation Method 2
forming a conductor circuit by electrolytic copper plating
Data Source
AI summary
The present invention provides a method for producing a printed wiring board having a circuit pattern on an electrically insulating substrate. The method includes step 1, forming an electrically conductive metal layer (M1) on an electrically insulating substrate (A), the electrically conductive metal layer (M1) containing silver particles; step 2, forming a patterned resist on the electrically conductive metal layer (M1), the patterned resist being a resist patterned by removing the portion thereof in the area in which the circuit is to be formed; step 3, forming a conductor-circuit layer (M2) by electrolytic plating; and step 4, peeling away the patterned resist and selectively removing, using an etchant, the electrically conductive metal layer (M1) in the area in which no circuit has been formed. This production method allows the manufacturer to produce a printed wiring board requiring no treatment such as surface roughening with chromic acid or permanganic acid or the formation of a surface altered layer with an alkali and without using vacuum equipment. The resulting printed wiring board has high adhesiveness between its substrate and conductor circuit, few undercuts, and a rectangular cross-sectional shape good for use as circuit wiring.