Reduction-Stage Pretreatment Liquid for Filler-Rich PCB Plating
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Solution Overview
Problem
The challenge of ensuring sufficient adhesion between insulating resin substrates containing fillers and copper plating films in printed wiring boards, particularly in high-density and high-precision applications, where surface roughness is low and filler content is high, is not adequately addressed by conventional desmear treatment methods.
Innovation Solution
A pretreating liquid for electroless plating that includes specific glycol ethers and a fluorine compound, used in combination with a reducing agent during reduction treatment, enhances filler removal and improves adhesion by penetrating into narrow gaps and promoting oxidation-reduction reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional desmear treatment methods are used, then the process is simple, but adhesion between insulating resin substrate and copper plating film is insufficient when surface roughness is low and filler content is high
Solution Approach 1:
The patent combines the reduction treatment and filler removal treatment into a single integrated process step. The pretreating liquid contains both reducing agents (for removing oxide residues) and filler removal agents (for removing filler particles), allowing simultaneous execution of multiple functions that were traditionally performed in separate steps, thereby improving adhesion without significantly increasing process complexity
Solution Approach 2:
The pretreating liquid is formulated as a composite solution containing multiple active components: reducing agents (such as hydroxylamine sulfate, hydrazine sulfate, or sodium hypophosphite), filler removal agents (such as fluorine compounds or organic solvents), and auxiliary agents. This composite formulation enables the liquid to perform multiple functions simultaneously - reducing oxides, removing filler, and preparing the surface for plating - thereby resolving the adhesion problem while maintaining process simplicity
2Manufacturing precision
If surface roughness is reduced for high-density and high-precision printed wiring boards, then manufacturing precision is improved, but adhesion to plating film deteriorates
Solution Approach 1:
The patent changes the chemical parameters of the pretreating liquid by incorporating specific filler removal agents alongside reducing agents. This chemical parameter modification allows effective filler removal even from smooth surfaces (low Ra values), creating sufficient adhesion sites without requiring mechanical roughening, thereby maintaining both manufacturing precision and adhesion strength
Solution Approach 2:
The pretreating liquid acts as an intermediary substance that chemically modifies the interface between the insulating resin substrate and the upcoming copper plating film. By removing filler particles and oxide residues through chemical action, it creates a clean, reactive surface that enhances adhesion without requiring physical roughness, thus enabling high-precision boards to achieve sufficient adhesion
3Stability of the object's composition
If filler content is increased to reduce thermal expansion coefficient, then thermal stability is improved, but adhesion with plating film becomes insufficient
Solution Approach 1:
The patent extracts (removes) filler particles from the insulating resin substrate surface during the pretreatment process. By incorporating filler removal agents in the pretreating liquid, the method selectively removes filler particles that would otherwise interfere with adhesion, while leaving the bulk material composition unchanged. This allows high filler content (for thermal stability) to coexist with good adhesion, as the filler particles on the surface are removed to create a clean bonding interface
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 achieves remarkable adhesion improvement between filler-containing insulating resin substrates and plating films, even with low surface roughness and high filler content, suitable for high-density and high-precision printed wiring boards.
Implementation Method 1
reduction treatment (also called neutralization treatment) for dissolving and removing a residue (such as manganese oxide derived from sodium permanganate) generated on the surface of a resin substrate by roughening treatment
Implementation Method 2
a fluorine compound having the effect of removing a filler during reduction treatment
Implementation Method 3
immersed in a roughening solution containing an oxidizing agent such as permanganate or chromate to roughen (etch) the surface of the insulating resin substrate
Data Source
Figure 1(a)~1(b)
AI summary
The present invention provides a novel pretreating liquid for electroless plating which is used simultaneously with reduction treatment after roughening treatment of a filler-containing insulating resin substrate. A pretreating liquid for electroless plating of the present invention is used simultaneously with reduction treatment when an insulating resin substrate containing a filler is roughened and residues generated on the insulating resin substrate are reduced. The pretreating liquid comprises: a reducing agent; and at least one selected from the group consisting of ethylene-based glycol ether represented by CmH(2m+1)-(OC2H4)n-OH (m = an integer of 1 to 4, n = an integer of 1 to 4) and propylene-based glycol ether represented by CxH(2x+1)-(OC3H6)y-OH (x = an integer of 1 to 4, y = an integer of 1 to 3),