Halogen-Free Epoxy Resin Composition for Printed Wiring Boards
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Solution Overview
Problem
Conventional epoxy resin compositions for printed wiring boards face challenges in achieving ignition resistance, solder heat resistance, and high temperature rigidity without using halogen compounds, while also maintaining low moisture absorptivity and chemical resistance.
Innovation Solution
An epoxy resin composition comprising a phosphorous compound with 1.8 to 3 phenolic hydroxyl groups, a bifunctional epoxy resin, a multifunctional epoxy resin, an inorganic filler with a thermal decomposition temperature above 400°C, and a curing agent, where the phenolic hydroxyl group is reacted with the bifunctional epoxy resin to adjust the epoxy equivalent ratio, and 20-55% of the preliminarily reacted epoxy resin is used, along with 20-180 parts of inorganic filler per 100 parts of resin solid content, to enhance ignition resistance and high temperature rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If halogen compounds (bromine compounds) are used to provide ignition resistance, then self-extinguishing properties are achieved, but hazardous compounds (dibenzodioxins, furans) are generated during combustion and heat resistance deteriorates over time
Solution Approach 1:
The patent removes halogen compounds (bromine compounds) from the epoxy resin composition entirely and replaces them with phosphorous compounds as the fire retardant agent. This extraction of the harmful substance while maintaining the desired function (ignition resistance) directly resolves the contradiction between achieving self-extinguishing properties and avoiding hazardous compound generation during combustion
Solution Approach 2:
The patent changes the chemical composition parameter from halogen-based fire retardants to phosphorous-based fire retardants. Specifically, it uses phosphorous ester compounds (such as triphenyl phosphate, tricresyl phosphate, cresyldiphenyl phosphate) at controlled concentrations (5-20 parts by mass per 100 parts by mass of epoxy resin) to achieve ignition resistance without the harmful effects of halogen compounds
2Object-affected harmful factors
If additive type phosphorous fire retardants are used to provide ignition resistance, then self-extinguishing properties are achieved, but solder heat resistance and chemical resistance deteriorate after moisture absorption
Solution Approach 1:
The patent applies preliminary action by pre-reacting the phosphorous fire retardant with the epoxy resin before final curing, forming a stable complex that prevents subsequent degradation. This preliminary reaction creates a more stable chemical structure that maintains solder heat resistance and chemical resistance even after moisture absorption, while still providing the required ignition resistance
Solution Approach 2:
The patent creates a composite material system where phosphorous ester compounds are combined with specific epoxy resins (bisphenol A type, bisphenol F type, or phenolic resin type) and curing agents (polyamide, polyimide, or phenolic resin). This composite approach ensures that the fire retardant properties are achieved while maintaining overall material performance including solder heat resistance
3Object-affected harmful factors
If reactive phosphorous fire retardants are used to provide ignition resistance, then self-extinguishing properties are achieved, but moisture absorptivity increases and solder heat resistance decreases
Solution Approach 1:
The patent carefully controls the concentration parameter of phosphorous compounds within a specific range (5-20 parts by mass per 100 parts by mass of epoxy resin) and selects specific types of phosphorous ester compounds. This parameter optimization achieves ignition resistance while limiting moisture absorptivity increases and maintaining solder heat resistance
4Object-generated harmful factors
If lead-free solder is used to address environmental concerns, then lead pollution is reduced, but treating temperature increases by 10-20°C requiring higher temperature rigidity
Solution Approach 1:
The patent modifies the thermal properties of the epoxy resin composition by optimizing the resin-curing agent-phosphorous compound system. This results in increased glass transition temperature (Tg) and higher temperature rigidity, enabling the material to withstand the elevated soldering temperatures (230-280°C) required for lead-free solder processes
5Object-affected harmful factors
If conventional epoxy resin composition is used to achieve ignition resistance without halogen compounds, then self-extinguishing properties are obtained, but high temperature rigidity and solder heat resistance do not reach required levels
Solution Approach 1:
The patent develops an optimized composite material system combining specific epoxy resins (bisphenol A type, bisphenol F type, or phenolic resin type) with specific curing agents (polyamide, polyimide, or phenolic resin) and phosphorous ester compounds. This composite formulation achieves a balance where ignition resistance, high temperature rigidity, and solder heat resistance all meet required performance levels simultaneously
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
The solution provides printed wiring boards with excellent ignition resistance, solder heat resistance, and high temperature rigidity without generating toxic substances on burning, while maintaining low moisture absorptivity and chemical resistance, and allowing for the use of lead-free solders with higher reflow temperatures.
Implementation Method 1
the phenolic hydroxyl group of the above phosphorous compound is reacted in advance with the above epoxy resin to yield a preliminarily reacted epoxy resin
Implementation Method 2
an inorganic filler with thermal decomposition temperature (weight loss by 5%) at 400°C or higher
Data Source
AI summary
An epoxy resin composition for a prepreg used in manufacturing a printed wiring board, particularly a multilayered printed wiring board, is provided. The composition features: (A) a multifunctional epoxy resin having on average 2.8 or more epoxy groups per molecule; (B) a reaction product of a phosphorous compound, a bifunctional epoxy resin, and an optional multifunctional epoxy resin, provided in an amount of 20% to 55% by mass, based on the total amount of epoxy resin, including (A) and (B); (C) a curing agent of dicyandiamide and/or a multifunctional phenolic compound; and (D) an inorganic filler blend containing an inorganic filler with a thermal decomposition temperature of 400° C. or above. The composition does not generate toxic substances when combusted and has excellent ignition resistance, solder heat resistance after moisture absorption, and high temperature rigidity.