Chip Resistor Mounting Layout with Flexible Electrodes for Thermal Shock
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Solution Overview
Problem
Conventional chip resistor mounting structures face challenges in thermal shock resistance, particularly when using high-strength lead-free solder, which can lead to solder cracks and peeling off of back surface electrodes due to rigid joint portions and inadequate stress absorption.
Innovation Solution
The chip component is designed with back surface electrodes that protrude inwardly from the lands on the circuit board, and are made of sintered silver or resin material with conductive particles, allowing for improved flexibility and stress absorption, thereby preventing peeling off and crack formation during thermal shocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength lead-free solder is used for mounting, then joint strength is improved, but thermal shock resistance deteriorates due to rigid joint portions
Solution Approach 1:
The back surface electrode is designed with different local properties: a thick portion with large film thickness positioned at the inner end provides flexibility and stress absorption, while other portions maintain adequate thickness for electrical connection. This local differentiation allows the electrode to exhibit both strength and flexibility in different regions, resolving the contradiction between joint strength and thermal shock resistance.
Solution Approach 2:
The invention changes the physical parameters of the back surface electrode, specifically controlling the film thickness distribution. By making the thick portion have a film thickness of 5 µm or more (while total thickness is 2 µm or more), the electrode gains sufficient flexibility to absorb thermal stress while maintaining electrical conductivity, thus improving thermal shock resistance without sacrificing joint strength.
2Volume of moving object
If back surface electrodes are made thin for compact design, then device size is reduced, but flexibility and stress absorption capability deteriorate
Solution Approach 1:
Instead of uniformly thinning the back surface electrode, the invention applies local quality by creating a thick portion with large film thickness at the inner end position. This localized thickening provides the necessary flexibility and stress absorption capability at the critical stress concentration point, while other portions can remain thinner to maintain compact overall dimensions.
3Manufacturing precision
If the distance between back surface electrodes is made equal to land separation, then electrical connection is optimized, but thermal stress concentration increases causing peeling
Solution Approach 1:
The invention applies beforehand cushioning by positioning the thick portion of the back surface electrode at the inner end, which is the location most susceptible to thermal stress and peeling. This pre-positioned flexible region acts as a cushion that absorbs thermal stress before it can cause damage, preventing peeling while maintaining proper electrical connection alignment with the lands.
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
This design enhances thermal shock resistance by distributing and relaxing thermal stress through the flexible back surface electrodes, preventing solder cracks and peeling off, even when using high-strength solder.
Implementation Method 1
the end face electrodes and the back surface electrodes being connected to the corresponding lands via solder
Data Source
AI summary
Provided is a mounting structure for a chip component having high thermal shock resistance. In amounting structure for a chip resistor 1 according to the present invention, a separation distance L1 between a pair of back surface electrodes 3 formed on an insulating substrate 2 of a chip resistor 20 is set to be shorter than a separation distance L2 between a pair of lands 31 provided on a circuit board 30. Each of the back surface electrodes 3 is formed with a thick portion (first electrode portion 3a), and an external electrode 9 deposited on the back surface electrode 3 is connected on the corresponding land 31 via solder 32 with a top portion of the thick portion made positioned directly above an inner end of the land 31.