Chip Resistor Protective Coating for Peeling and Moisture Resistance
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Solution Overview
Problem
Chip resistors face issues with peeling between the protective coating and the underlying member, and water ingress due to poor adhesion and shrinkage, leading to resistance value variations under heat and humidity tests.
Innovation Solution
A chip resistor with a protective coating composed of a cured product of a coating agent containing polyfunctional epoxy resin, silica as the inorganic filler (60-90% by weight), and silicone rubber particles (1-15% by weight), which relaxes stress and improves adhesion, reducing peeling and water ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a protective coating is formed on the chip resistor, then heat resistance is improved, but peeling occurs between the protective coating and the underlying member due to shrinkage
Solution Approach 1:
The patent changes the chemical composition parameters of the coating agent by specifying precise weight ratios of polyfunctional epoxy resin (30-70%), monofunctional epoxy resin (10-40%), and inorganic filler (5-40%). This parameter optimization allows the coating to achieve both high heat resistance and reduced shrinkage, preventing peeling while maintaining adhesion strength.
Solution Approach 2:
The patent uses a composite coating system combining multiple epoxy resins (polyfunctional and monofunctional) with inorganic fillers. This composite structure provides synergistic effects where the polyfunctional epoxy resin contributes to heat resistance while the monofunctional epoxy resin and inorganic filler reduce shrinkage, thereby preventing peeling.
2Stability of the object's composition
If the protective coating shrinks during curing, then adhesion to the underlying member deteriorates, but water can enter through the gap
Solution Approach 1:
The patent optimizes the inorganic filler content to 5-40% by weight and selects specific filler materials to control the coefficient of linear expansion. This parameter control minimizes shrinkage during curing, maintaining coating integrity and preventing gaps that would allow water ingress.
Solution Approach 2:
The patent addresses thermal expansion mismatch between the coating and underlying member by carefully selecting inorganic fillers with appropriate thermal expansion coefficients. This reduces differential shrinkage during curing and thermal cycling, preventing gap formation and subsequent water penetration.
3Temperature
If inorganic filler content is increased to improve heat resistance, then coating brittleness increases, but adhesion decreases
Solution Approach 1:
The patent creates a balanced composite formulation where inorganic fillers (providing heat resistance) are combined with both polyfunctional and monofunctional epoxy resins (providing flexibility). The specific ratio range of 5-40% inorganic filler ensures sufficient heat resistance while the organic resin matrix maintains coating flexibility and adhesion.
Solution Approach 2:
The patent specifies precise parameter ranges for inorganic filler content (5-40%) and resin ratios to optimize the balance between heat resistance and flexibility. This controlled parameter variation prevents excessive brittleness while maintaining high temperature resistance.
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 enhances heat resistance, reduces peeling, and minimizes resistance value variations by relaxing stress and improving adhesion, ensuring the chip resistor performs consistently under severe thermal and humidity conditions.
Implementation Method 1
the silicone rubber particles relax stress, reducing peeling and water ingress
Implementation Method 2
The protective coating is a cured product of a coating agent containing a polyfunctional epoxy resin, a curing agent
Data Source
AI summary
A chip resistor includes: a resistor body; and a protective coating that covers the resistor body. The protective coating is a cured product of a coating agent containing a polyfunctional epoxy resin, a curing agent, an inorganic filler, and silicone rubber particles. The coating agent contains: silica as the inorganic filler at a content equal to or greater than 60% by weight and equal to or less than 90% by weight; and the silicone rubber particles at a content equal to or greater than 1% by weight and equal to or less than 15% by weight.