Resistive Metal Foil Adhesion and Resistance Stability
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Solution Overview
Problem
Conventional metal foils with electrically resistive layers face challenges in maintaining high peel strength and low resistance value variation, particularly due to surface roughness and adhesive force issues between the resistive layer and the resin, which are not adequately addressed by existing surface roughening methods.
Innovation Solution
A metal foil with a controlled surface roughness of 4.0 to 6.0 μm, featuring a copper-zinc alloy layer and a stabilizing layer of zinc oxide, chromium oxide, or nickel oxide, combined with a Si-containing NiCrAlSi alloy resistive layer, enhances adhesiveness and maintains low resistance value variation within ±10%, thereby improving peel strength and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If surface roughness is increased to enhance adhesive strength, then peel strength between copper foil and resistive layer improves, but resistance value variation increases and high-frequency characteristics deteriorate
Solution Approach 1:
The invention optimizes the surface roughness parameter by controlling the ten-point average roughness Rz to be 3.0 μm or less, as measured by an optical method. This parameter optimization resolves the contradiction by maintaining peel strength while minimizing resistance value variation and improving high-frequency characteristics.
Solution Approach 2:
The invention applies different surface quality requirements to different functional layers. The copper foil surface is controlled to have Rz ≤ 3.0 μm for the resistive layer to ensure low resistance variation, while the overall surface may have controlled roughness for adhesive purposes, creating local quality differentiation.
2Manufacturing precision
If surface roughness is reduced to improve resistance value stability, then resistance variation decreases, but adhesive strength and peel strength deteriorate
Solution Approach 1:
The invention changes the surface roughness parameter to a specific range (Rz ≤ 3.0 μm) that simultaneously satisfies both adhesive strength requirements and resistance value stability requirements, eliminating the need to trade one for the other.
Solution Approach 2:
The invention introduces a stabilizing layer as an intermediary between the copper foil and the resistive layer. This stabilizing layer mediates the interaction between the two layers, providing adequate adhesive strength while allowing the copper foil surface to maintain low roughness for resistance stability.
3Strength
If conventional roughening treatment is applied to copper foil, then adhesive strength improves, but the characteristics of electrically resistive layer cannot be maintained
Solution Approach 1:
The invention performs preliminary surface preparation by controlling the copper foil surface roughness before applying the resistive layer. By pre-establishing the optimal surface condition (Rz ≤ 3.0 μm), the subsequent resistive layer can maintain its electrical characteristics while achieving adequate adhesion.
Solution Approach 2:
The invention changes the surface roughness parameter from conventional high roughness values to a precisely controlled low roughness value (Rz ≤ 3.0 μm), which fundamentally alters the interaction between the copper foil and resistive layer, allowing both adhesive strength and resistive layer characteristics to be maintained.
Data Source
AI summary
Metal foil provided with an electrically resistive layer, characterized in that an alloy (in particular, a NiCrAlSi alloy) resistive layer containing 1 to 6 mass % of Si is formed on the metal foil controlled to have a ten-point average roughness Rz, which was measured by an optical method, of 4.0 to 6.0 μm, and the variation in the resistance value of the electrically resistive layer is within ±10%. Provided is a copper foil that allows embedding of a resistive material in a board by further forming an electrically resistive layer on the copper foil, and further allows improving the adhesiveness and suppressing the variation in resistance value within a certain range. As needed, metal foil provided in advance with a copper-zinc alloy layer formed on the surface thereof and a stabilizing layer composed of at least one component selected from zinc oxide, chromium oxide, and nickel oxide formed on the copper-zinc alloy layer is used.