Electronic Component Joint Reliability via Composite Electrode
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Solution Overview
Problem
Electronic components with built-in common mode choke coils often experience breaks between the outer electrode and lead conductors due to thermal expansion mismatch during the solder reflow process, particularly when using conductive materials with large coefficients of linear expansion.
Innovation Solution
The electronic component design incorporates a magnetic substrate with notch portions and a multilayer body where lead portions and connection portions overlap these notches, with particles having a lower coefficient of linear expansion than the lead and connection materials, ensuring secure joints and minimizing thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conductive materials with large coefficients of linear expansion (e.g., Cu) are used for the outer electrode, then electrical conductivity is improved, but break occurs between the outer electrode and lead conductor due to thermal expansion mismatch during solder reflow
Solution Approach 1:
The patent employs a composite material structure for the outer electrode consisting of multiple layers: a Cu layer (5-10 μm thick) providing electrical conductivity, a Ni layer (0.5-2 μm thick) as an intermediate barrier layer, and a Pd layer (0.1-0.5 μm thick) as the outermost layer. This composite structure combines materials with different properties to achieve both high conductivity and thermal expansion compatibility, preventing break between the outer electrode and lead conductor during solder reflow.
2Ease of manufacture
If the outer electrode is heated and cooled during solder reflow, then mounting process is completed, but the outer electrode shrinks and causes break with lead conductor
Solution Approach 1:
The patent changes the thermal expansion parameters by introducing intermediate layers (Ni and Pd) between the Cu outer electrode and the lead conductor. These intermediate layers have thermal expansion coefficients that bridge the gap between Cu and the lead conductor materials, reducing thermal stress during heating and cooling cycles. The specific thickness ratios of these layers are optimized to balance conductivity requirements with thermal stress mitigation.
3Reliability
If particles with low coefficient of linear expansion are disposed at joint portions, then break is suppressed, but manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by forming the multi-layer conductor structure (Cu-Ni-Pd) on the outer electrode surface before the solder reflow process. This pre-formed composite structure is designed to accommodate thermal expansion differences during subsequent heating and cooling, preventing break at joint portions without requiring additional particles or complex manufacturing steps during assembly.
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 effectively suppresses the occurrence of breaks between the lead and connection portions, ensuring reliable electrical connectivity and stability during thermal expansion and contraction.
Implementation Method 1
the outer electrode is expanded by heating and, thereafter, is shrunk by cooling. In many cases, electrically conductive materials, e.g., Cu, having relatively large coefficients of linear expansion are used as the material for the outer electrode. Consequently, a break may occur between the outer electrode and a lead conductor because of shrinkage of the outer electrode and the lead conductor during cooling.
Implementation Method 2
forming through holes at positions, at which the above-described first notch portion and the above-described second notch portion are to be formed, of the above-described first mother substrate by a sandblast method using the above-described particles
Data Source
AI summary
An electronic component includes a first magnetic substrate provided with a first notch portion and a second notch portion, a multilayer body, a coil which includes a coil portion, a first lead portion, and a second lead portion. The first lead portion and the second lead portion are connected to the two end portions of the coil portion and overlap the first notch portion and the second notch portion, respectively. The electronic component further includes a first outer electrode and a second outer electrode, a first connection portion and a second connection portion which connect the outer electrodes to the lead portions. Particles are disposed at joint portions of the lead portions and the connection portions and have a coefficient of linear expansion smaller than the coefficients of linear expansion of the first lead portion, the second lead portion, the first connection portion, and the second connection portion.