Laser-Bored Multilayer PCB via Black Chromium Oxide Layer
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Solution Overview
Problem
Current methods for forming via holes in multi-layered printed wiring boards using lasers face challenges such as low productivity and the need for precise etching of copper foils, which can result in undercut formation and thin line issues during fine wiring formation.
Innovation Solution
A production method involving a metal foil with an adhesive layer, where a thin metal foil and organic adhesive layer are laminated with an organic insulating resin, laser-bored to create blind via holes, and then processed to form a fine outer layer circuit connected with the inner layer circuit, using a thermosetting resin composition with an epoxy resin and inorganic filler to prevent undercut and ensure good adhesiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick copper foil is used as the outer layer, then the mechanical strength and electrical conductivity are improved, but laser boring becomes difficult due to laser beam reflection
Solution Approach 1:
A black chromium oxide layer is formed on the copper foil surface before laser boring through chemical oxidation treatment. This preliminary surface modification enables the copper foil to absorb laser energy effectively while maintaining its thick structure for mechanical strength and electrical conductivity.
2Ease of manufacture
If copper foil is removed by etching before laser boring, then laser boring becomes possible, but productivity is significantly reduced
Solution Approach 1:
The copper foil surface is pre-treated with chemical oxidation to form a black chromium oxide layer that enables direct laser boring without etching. This preliminary surface modification eliminates the need for time-consuming etching processes while maintaining laser processability.
Solution Approach 2:
The mechanical/chemical etching process is replaced by a chemical oxidation treatment that creates a laser-absorbing surface layer. This substitution eliminates the need for material removal while achieving the same laser processability goal.
3Productivity
If ultrathin copper foil is used for direct laser boring, then productivity is improved, but fine wiring formation becomes difficult due to large etching quantity
Solution Approach 1:
The copper foil thickness is optimized to 5-20 μm, and the surface is chemically oxidized to form a black chromium oxide layer. This parameter combination enables direct laser boring with high productivity while reducing the etching quantity to 1-5 μm for precise fine wiring formation.
4Use of energy by moving object
If the copper foil surface is chemically oxidized to form a black chromium oxide layer, then laser absorption is improved, but additional processing steps are required
Solution Approach 1:
The copper foil surface is chemically oxidized using potassium permanganate solution to form a black chromium oxide layer. This simple chemical treatment dramatically improves laser absorption efficiency, enabling effective laser boring of thick copper foils without complex additional equipment.
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 enhances the efficiency of forming fine outer layer circuits in multi-layered printed wiring boards by preventing undercut formation and ensuring good adhesiveness to plated copper, improving productivity and circuit quality.
Implementation Method 1
a step of irradiating the laminated sheet with a laser to bore the outer layer metal foil layer, the organic adhesive layer, and the organic insulating resin layer to form a laminated sheet having a blind via hole
Implementation Method 2
an inorganic filler having a specific surface area of 20 m2/g or more, the content of the inorganic filler being 1 to 10 parts by mass based on 100 parts by mass of the epoxy resin
Data Source
AI summary
Disclosed is a production method of a multi-layered printed wiring board, including the following steps 1 to 3:Step 1: a step of laminating, on a substrate with inner layer circuit, a metal foil with adhesive layer including a support, a metal foil having a thickness of 3 μm or less and ⅙ or less relative to the thickness of the inner layer circuit, and an organic adhesive layer having a thickness of 10 μm or less in this order, via an organic insulating resin layer such that the organic insulating resin layer and the organic adhesive layer are opposed to each other, and then releasing the support to form a laminated sheet (a) having the metal foil as an outer layer metal foil layer;Step 2: a step of irradiating the laminated sheet (a) with a laser to bore the outer layer metal foil layer, the organic adhesive layer, and the organic insulating resin layer to form a bored laminated sheet (b) having a blind via hole; andStep 3: a step of forming an outer layer circuit connected with the inner layer circuit through the following steps 3-1 to 3-4:Step 3-1: a step of etching removing the outer layer metal foil layer of the bored laminated sheet (b) formed in the step 2 and then forming an outer layer copper layer having a thickness of 2 μm or less on the bored laminated sheet (b);Step 3-2: a step of forming a resist pattern by a resist applied on the outer layer copper layer;Step 3-3: a step of forming a circuit layer on the surface of the outer layer copper layer on which the resist pattern is not formed, by electrolytic copper plating; andStep 3-4: a step of removing the resist pattern and then removing the exposed outer layer copper layer by etching, thereby forming an outer layer circuit connected with the inner layer circuit.