Resin Composition for High-Frequency PCBs
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Solution Overview
Problem
Conventional laminates for high-frequency printed wiring boards face challenges with heat resistance after moisture absorption, lead-free solder reflow, and dimensional stability, particularly in high-multilayer boards, where resin recession and delamination occur due to insufficient heat resistance and moldability issues with polyphenylene ether and cyanate ester resins.
Innovation Solution
A resin composition combining bisphenol A type epoxy resin, novolak type epoxy resin, and cyanate ester resin, with spherical silica as an inorganic filler, is developed, optimizing the equivalent ratio of cyanate groups to epoxy groups and using a specific secondary hydroxyl group amount to enhance heat resistance and lead-free solder reflow properties, while maintaining dimensional stability and electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyphenylene ether resin is used for high-frequency laminates, then a low dielectric constant and low dielectric loss tangent are achieved, but the melting point is high causing insufficient flowing characteristics and poor moldability
Solution Approach 1:
The patent uses a composite resin system combining cyanate ester resin (for low dielectric properties), bisphenol A type epoxy resin (for flow characteristics), and novolak type epoxy resin (for heat resistance). This composite approach allows each component to contribute its strengths: cyanate ester provides electrical performance, while the epoxy resins provide moldability and processing characteristics that pure cyanate ester lacks.
2Ease of manufacture
If cyanate ester resin is used for laminates, then low dielectric constant and low dielectric loss tangent are achieved with excellent moldability, but heat resistance after moisture absorption is insufficient under lead-free soldering conditions
Solution Approach 1:
The patent combines cyanate ester resin with bisphenol A type epoxy resin and novolak type epoxy resin to create a composite system where the epoxy components provide enhanced heat resistance and moisture resistance while the cyanate ester maintains low dielectric properties. The synergistic effect resolves the contradiction between moldability and heat resistance.
Solution Approach 2:
The patent optimizes the equivalent ratio of cyanate groups to epoxy groups (0.7-1.45) and controls the secondary hydroxyl group amount (0.4 meq/g or less) to achieve the desired balance between heat resistance and other properties. By adjusting these chemical parameters, the resin composition achieves both adequate heat resistance and proper flow characteristics.
3Adaptability or versatility
If high-multilayer printed wiring boards are produced, then high frequency and high multilayer capabilities are achieved, but resin recession occurs from end portions of inner layer patterns and delamination occurs due to large plate thickness
Solution Approach 1:
The composite resin system provides balanced properties that enable high-multilayer construction: the cyanate ester component ensures low dielectric loss for high-frequency performance, while the epoxy components provide sufficient strength and dimensional stability to prevent resin recession and delamination in thick multilayer boards.
Solution Approach 2:
By controlling the equivalent ratio and hydroxyl group content, the patent optimizes the resin's mechanical properties and adhesion characteristics, enabling it to maintain dimensional stability in high-multilayer applications despite the increased plate thickness and associated stresses.
4Ease of repair
If the number of reflow treatments is increased for repairs, then mounted part repairs are enabled, but heat resistance requirements become more severe due to accumulated thermal stress
Solution Approach 1:
The patent adjusts the chemical composition parameters (equivalent ratio, hydroxyl group content) to enhance the resin's thermal stability and moisture resistance, allowing it to withstand multiple reflow cycles without degrading. This enables repeated repairs while maintaining joint strength and preventing delamination.
Data Source
AI summary
A resin composition excellent in heat resistance after moisture absorption, lead-free solder reflow properties, dimensional stability and electrical characteristics for high-multilayer and high-frequency-capable printed wiring boards, which composition comprises a bisphenol A type epoxy resin (a) having at least two epoxy groups per molecule and a secondary hydroxyl group amount of 0.4 meq/g or less, a novolak type epoxy resin (b) at least two epoxy groups per molecule, a cyanate ester resin (c) having at least two cyanate groups per molecule and spherical silica having an average particle diameter of 4 μm or less, wherein the equivalent ratio of cyanate groups/epoxy groups in the resin composition is in the range of 0.7 to 1.45, and a prepreg and a metal-foil-clad laminate each of which comprises the resin composition.