Chip Resistor Back Electrode Structure for Solder Crack Prevention
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Solution Overview
Problem
Chip resistors experience cracks in the solder due to thermal stress when mounted on wiring boards, disrupting the current path and requiring measures to prevent such cracks.
Innovation Solution
A chip resistor design featuring a substrate with top and back surfaces, paired electrodes, and side electrodes, where each back electrode has a first insulating layer and a second layer made of metal particles and synthetic resin, reducing thermal stress and preventing solder cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer back electrode is used, then the structure is simple, but thermal stress causes cracks in the solder
Solution Approach 1:
The back electrode is divided into two distinct layers: a first layer (base layer) and a second layer (protective layer). This segmentation allows each layer to perform specific functions - the first layer provides structural support and electrical conductivity, while the second layer specifically addresses thermal stress and prevents solder cracks, thereby resolving the contradiction between reliability improvement and structural complexity.
Solution Approach 2:
The second layer is constructed as a composite material containing metal particles dispersed in a glass frit matrix. This composite structure combines the advantages of metal particles (electrical conductivity, thermal resistance) and glass frit (stress absorption, adhesion), enabling the back electrode to reduce thermal stress effectively while maintaining electrical functionality, thus preventing solder cracks without excessive complexity.
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 two-layer back electrode configuration effectively reduces thermal stress on the solder, preventing cracks and enhancing adhesion while maintaining electrical conductivity, thus ensuring reliable chip resistor performance.
Implementation Method 1
heat is generated from the resistor element. This causes the thermal stress due to the difference in thermal strain between the back electrodes and the solder to act on the solder
Data Source
AI summary
A chip resistor includes a substrate, two top electrodes, a resistor element, two back electrodes, and two side electrodes. The substrate has a top surface, a back surface and two side surface. The top and back surfaces face away in the thickness direction of the substrate. The side surfaces, spaced apart in a predetermined direction orthogonal to the thickness direction, are connected to the top and back surfaces. The top electrodes, spaced apart in the predetermined direction, are in contact with the top surface. The resistor element, disposed on the top surface, is connected to the top electrodes. The back electrodes, spaced apart in the predetermined direction, are in contact with the back surface. The side electrodes, held in contact with the side surfaces, are connected to the top and back electrodes. Each back electrode has a first and a second layer. The first layer is in contact with the back surface. The second layer, covering a part of the first layer, is made of a material containing metal particles and synthetic resin.