PCB Via Hole Formation Using Laser Desmear on Both Surfaces
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Solution Overview
Problem
Conventional printed wiring boards face challenges in achieving higher density and mechanical strength due to difficulties in via hole processing, such as warping and fracture, especially when drilling through both insulating resin and metal foils, and the powerful spray washing methods used to remove residues can damage copper foils.
Innovation Solution
The method involves forming via holes on both surfaces of a metal-clad laminated sheet with a thermosetting resin and metal foils, using a CO2 laser for precise drilling, and performing desmear treatment to remove residues without causing warping, allowing for high-density and high-strength printed wiring boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drilling is performed for both surfaces to form via holes, then connection reliability is improved, but warping and fracture occur
Solution Approach 1:
The patent applies preliminary action by performing desmear treatment before final via hole completion. The process sequence is: (1) drill via holes through both surfaces, (2) perform desmear treatment to remove resin residues from hole bottoms, (3) complete via hole formation. This preliminary desmear step prevents subsequent warping and fracture by eliminating weak points in the resin structure before final assembly.
Solution Approach 2:
The patent replaces the conventional mechanical spray washing method with a chemical desmear treatment process. Instead of using high-pressure mechanical spray washing that causes warping and fracture, the invention uses chemical solutions to remove residues. The desmear treatment uses oxidizing agents or enzymes to chemically dissolve resin residues without applying mechanical stress to the substrate.
2Manufacturing precision
If spray washing is used to remove residues, then cleaning effectiveness is improved, but copper foils are damaged
Solution Approach 1:
The patent replaces mechanical spray washing with chemical desmear treatment. The desmear process uses chemical solutions (oxidizing agents like chromic acid or permanganic acid, or enzymatic solutions) to remove resin residues through chemical dissolution rather than mechanical force. This eliminates the high-pressure spray impact that damages copper foils while effectively removing residues from via hole bottoms.
Solution Approach 2:
The patent changes the fundamental parameter of the cleaning process from mechanical (spray pressure, flow rate) to chemical (solution composition, temperature, exposure time). By adjusting chemical parameters such as solution concentration, temperature, and treatment duration, the process achieves effective residue removal without the mechanical stress that causes copper foil damage in spray washing methods.
3Productivity
If via hole density is increased for higher packaging density, then device miniaturization is improved, but mechanical strength deteriorates
Solution Approach 1:
The patent applies preliminary desmear treatment to via hole bottoms before final assembly when via holes are densely packed. This preliminary action removes resin residues that would create weak points in the high-density via structure. By treating each via hole individually through desmear, the process maintains mechanical strength even when via holes are closely spaced, enabling higher packaging density without sacrificing structural integrity.
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 enables the production of printed wiring boards with superior mechanical strength and higher density, preventing warping and residue-related issues, while allowing for precise placement of many via holes, thus meeting the demands of smaller and more performant electronic devices.
Implementation Method 1
using a CO2 laser for precise drilling
Data Source
Figure 1~3
Figure 4(a)~4(b)
Figure 5~6(b)
AI summary
The method for producing a printed wiring board according to the present invention with use of a metal-clad laminated sheet including a metal foil laminated on each of both surfaces of an insulating resin base material, the method at least including: a step (1) of irradiating a predetermined position in a surface (A) of the metal-clad laminated sheet with a laser to provide a via hole leading to the metal foil in a surface opposite to the surface (A); and a step (2) of irradiating a predetermined position in a surface (B), located in the opposite side to the surface (A), of the metal-clad laminated sheet with a laser to provide a via hole leading to the metal foil in a surface opposite to the surface (B).