Electronic Substrate Pad Layout for Thermal Shock Reliability
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Solution Overview
Problem
The coefficient of thermal expansion mismatch between a light-emitting diode (LED) and its base, such as glass, leads to cracks in the base or peeling of the LED during thermal shock tests, resulting in dark spots.
Innovation Solution
The electronic substrate design includes a protruding portion and a bonding pad where the bonding pad is not overlapped with the boundary of the protruding portion, creating a gap to reduce stress and improve solder joint flatness, thereby reducing the likelihood of base cracking and LED peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the bonding pad is positioned to overlap with the protruding portion boundary, then the solder joint flatness is improved, but the base cracking rate increases due to thermal expansion mismatch stress
Solution Approach 1:
The bonding pad is strategically positioned within the flat region of the protruding portion, avoiding the boundary area where stress concentrates. This local positioning optimization ensures that the bonding pad benefits from the flat surface for good solder joint formation while avoiding the high-stress boundary region that would cause base cracking during thermal cycling.
Solution Approach 2:
The invention changes the positional parameter of the bonding pad relative to the protruding portion boundary. By adjusting the bonding pad location to be entirely within the flat region and not overlapping with the boundary, the design optimizes both solder joint quality and structural reliability under thermal stress.
2Reliability
If the bonding pad is positioned away from the protruding portion boundary, then the base cracking rate is reduced, but the solder joint flatness may be compromised
Solution Approach 1:
The bonding pad is positioned within the flat region of the protruding portion, utilizing the locally flat surface to ensure good solder joint formation. This local positioning within the flat region simultaneously achieves both solder joint quality and reduced stress concentration.
3Strength
If the protruding portion boundary overlaps with the bonding pad, then the structural support is enhanced, but the thermal shock resistance deteriorates due to stress concentration
Solution Approach 1:
The bonding pad is positioned within the flat region away from the boundary, utilizing the locally flat and supported area for optimal bonding while avoiding the boundary region where stress concentrates during thermal expansion and contraction.
Solution Approach 2:
The flat region of the protruding portion acts as an intermediary zone between the bonding pad and the boundary. By positioning the bonding pad within this intermediate flat region, the design provides both structural support and stress relief, preventing direct stress transmission to the bonding pad during thermal cycling.
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 reduces the base cracking rate from 11.5% to 2% and maximum stress from 2905 MPa to 752 MPa, enhancing the reliability of the electronic device.
Implementation Method 1
coefficient of thermal expansion (CTE) mismatch readily occurs between the LED and the base (such as glass), thus leading to cracks in the base or peeling of the LED
Implementation Method 2
when a base welded with a light-emitting diode (LED) is subjected to a thermal shock test
Data Source
AI summary
An electronic substrate and an electronic device are provided. The electronic substrate includes a base, a conductive electrode, and a first layer. The conductive electrode and the first layer are disposed on the base, the first layer surrounds the conductive electrode and overlaps an edge portion of the conductive electrode. In a cross-sectional view, the first layer is divided into a first part and a second part, the conductive electrode is located between the first part and the second part, and a width of the first part is different from a width of the second part.