LED Substrate Bonding Pad Layout for Thermal Shock Reliability
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Solution Overview
Problem
Electronic substrates with light-emitting diodes (LEDs) face reliability issues due to coefficient of thermal expansion mismatch between the LED and the base, leading to cracks or peeling during thermal shock tests, especially when the bonding pad overlaps with the boundary of the protruding portion.
Innovation Solution
The design includes a bonding pad that is not overlapped with the boundary of the protruding portion, creating a gap to reduce stress and improve solder joint flatness, thereby minimizing the likelihood of base cracking or LED peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bonding pad is positioned to overlap with the boundary of the protruding portion, then the electrical connection is simplified, but the stress concentration increases leading to base cracking and LED peeling
Solution Approach 1:
The patent extracts the bonding pad from the high-stress boundary region of the protruding portion. By repositioning the bonding pad to be completely inside or outside the protruding portion boundary rather than overlapping it, the design removes the bonding pad from the stress concentration zone, thereby reducing stress while maintaining electrical connection functionality
Solution Approach 2:
The patent introduces an intermediary spatial relationship between the bonding pad and the protruding portion boundary. Instead of direct overlap (which causes stress concentration), the bonding pad is positioned with a clear separation from the boundary, acting as an intermediary configuration that reduces stress transmission while preserving the electrical connection function
2Ease of manufacture
If the bonding pad overlaps with the boundary of the protruding portion, then the manufacturing process is simplified, but cracks occur in the base during thermal shock tests
Solution Approach 1:
The patent extracts the bonding pad from the harmful boundary overlap region. By repositioning the bonding pad to avoid the protruding portion boundary completely, the design removes the source of stress concentration that leads to crack formation during thermal shock tests, thereby eliminating this harmful effect while maintaining manufacturability
3Area of stationary object
If the bonding pad overlaps with the boundary of the protruding portion, then the device structure is compact, but peeling of the LED occurs due to CTE mismatch
Solution Approach 1:
The patent extracts the bonding pad from the high-stress boundary region where CTE mismatch causes peeling. By repositioning the bonding pad to avoid overlapping the protruding portion boundary, the design removes the bonding pad from the zone where thermal expansion differences between LED and base cause stress concentration and subsequent peeling
Solution Approach 2:
The patent applies local quality by creating different spatial zones: the bonding pad is positioned in a low-stress region (either completely inside or outside the protruding portion boundary) while the protruding portion maintains its structural function. This localized repositioning protects the bonding interface from CTE mismatch stresses without compromising the overall device structure
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 decreases 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
Data Source
AI summary
An electronic substrate and an electronic device are provided. The electronic substrate includes a base, a protruding portion, and a bonding pad. The protruding portion and the bonding pad are disposed on the base. The bonding pad is not overlapped with a boundary of the protruding portion.