Chip Resistor Stress Relaxation Layer for Thermal Expansion
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Solution Overview
Problem
Conventional chip resistors experience stress and cracking due to thermal expansion differences between the chip resistor substrate and the circuit board, particularly in automotive applications where the chip resistor is larger, leading to potential failure under temperature cycles.
Innovation Solution
A chip resistor design featuring a substrate with a stress relaxation layer made of flexible materials like silicone or epoxy resin, a metal thin film layer, and a plating layer, which alleviates thermal expansion stress by allowing deformation and facilitates plating layer formation, reducing direct contact and enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a large chip resistor substrate is used, then the chip resistor can be used in automotive applications, but stress from thermal expansion difference increases causing solder material cracks
Solution Approach 1:
A stress relaxation layer made of flexible resin material is introduced between the substrate and the metal thin film layer. This intermediary layer absorbs and relaxes the stress generated by thermal expansion differences between the large substrate and the circuit board, preventing stress transmission to the solder material and eliminating cracks.
Solution Approach 2:
The stress relaxation layer changes the mechanical parameters of the structure by introducing a flexible material with different elasticity and thermal expansion characteristics. This parameter change allows the system to accommodate thermal stress without transmitting it to critical components like the solder material.
2Reliability
If a stress relaxation layer is added, then thermal expansion stress is alleviated, but the structure becomes more complex
Solution Approach 1:
The stress relaxation layer is implemented as a thin flexible film made of resin material. This thin-film approach provides effective stress relaxation functionality while minimizing the increase in structural complexity and maintaining a compact chip resistor design.
3Ease of manufacture
If a metal thin film layer is formed on the stress relaxation layer, then plating layer formation is facilitated, but direct contact between plating and stress relaxation layer is reduced
Solution Approach 1:
The metal thin film layer serves as an intermediary between the stress relaxation layer and the plating layer. It provides a suitable surface for plating formation while preventing direct contact between the plating layer and the stress relaxation layer, thus maintaining stress relaxation effectiveness while enabling manufacturing.
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 effectively suppresses crack generation by accommodating thermal expansion differences and ensures reliable operation by reducing stress on the solder material, thereby enhancing the chip resistor's durability and performance.
Implementation Method 1
If there is a significant difference between thermal expansion of the circuit board 101 and thermal expansion of a substrate 1 of the chip resistor A100, in the case of applying a temperature cycle, stress resulting from the thermal expansion difference is applied on the solder material 103
Implementation Method 2
a stress relaxation layer having flexibility and formed on the mounting surface of the substrate
Implementation Method 3
the metal thin film layer includes a sputtered layer
Data Source
AI summary
The present invention provides a chip resistor and a method of making the same for alleviating stress resulted from thermal expansion difference and thus suppressing cracks. A chip resistor includes: a substrate, having a carrying surface and a mounting surface facing away from each other; a pair of upper electrodes, disposed at two ends of the carrying surface; a resistor, disposed on the carrying surface and between the pair of upper electrodes, and electrically connected to the pair of upper electrodes; a stress relaxation layer having flexibility and formed on the mounting surface of the substrate; a metal thin film layer, formed on a surface of the stress relaxation layer opposite to the substrate; a side electrode for electrically connecting the upper electrodes and the metal thin film layer; and a plating layer covering the side electrode and the metal thin film layer.