High-Frequency PCB Substrate with Controlled Filler Distribution
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Solution Overview
Problem
The adhesive strength between the dielectric layer and the copper foil in high-frequency printed wiring boards is insufficient when using a fluororesin with an inorganic filler, leading to compromised high-frequency characteristics due to the need for increased copper foil roughness.
Innovation Solution
A substrate design with a dielectric layer comprising fluororesin and inorganic filler, where the copper foil has a maximum height roughness (Rz) of less than or equal to 2 µm, and specific ratios of inorganic filler distribution across different regions from the copper foil, ensuring improved adhesive strength and high-frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fluororesin with inorganic filler is used as the dielectric layer material, then the high-frequency characteristic is improved, but the adhesive strength between the dielectric layer and copper foil becomes insufficient
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of inorganic filler within the dielectric layer. The filler concentration varies from the copper foil interface toward the opposite surface, with higher concentration near the interface to enhance adhesion and lower concentration away from the interface to maintain high-frequency characteristics. This spatial variation in filler distribution allows simultaneous optimization of both adhesive strength and high-frequency performance.
Solution Approach 2:
The patent uses composite materials by combining fluororesin with inorganic filler particles to create a dielectric layer that maintains the low dielectric loss properties of fluororesin while adding adhesion enhancement through the filler. The composite structure allows the fluororesin matrix to provide high-frequency stability while the inorganic filler, particularly when concentrated near the copper interface, provides anchoring points for improved adhesive bonding.
2Strength
If the copper foil roughness is increased to improve adhesive strength, then the adhesive strength increases, but the high-frequency characteristic deteriorates
Solution Approach 1:
The patent applies local quality by concentrating the adhesion enhancement function in the dielectric layer rather than the copper foil. By creating a filler-rich region at the copper interface within the dielectric layer, the patent achieves strong adhesion without requiring increased copper foil roughness, thereby preserving the smooth surface needed for high-frequency performance.
3Ease of manufacture
If the inorganic filler is uniformly distributed in the dielectric layer, then the manufacturing process is simplified, but the adhesive strength at the copper foil interface is insufficient
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through gradient filler distribution. While uniform distribution would simplify manufacturing, the patent deliberately creates a non-uniform distribution with higher filler concentration near the copper interface. This can be achieved through controlled processing methods such as directional consolidation or gradient curing, which add manageable complexity to the manufacturing process while dramatically improving interfacial adhesion.
Data Source
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AI summary
A first embodiment of a substrate for a high-frequency printed wiring board according to the present disclosure is directed to a substrate for a high-frequency printed wiring board, the substrate including: a dielectric layer including a fluororesin and an inorganic filler; and a copper foil layered on at least one surface of the dielectric layer, wherein a surface of the copper foil at the dielectric layer side has a maximum height roughness (Rz) of less than or equal to 2 µm, and a ratio of the number of inorganic atoms of the inorganic filler to the number of fluorine atoms of the fluororesin in a superficial region of the dielectric layer at the copper foil side is less than or equal to 0.08.