Step Cut Lead Reduces Solder Joint Cracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional semiconductor devices experience malfunction or failure due to cracking of solder connections between leads and printed circuit boards (PCBs) under thermal fluctuations, caused by differing thermal expansions of materials used in the connection.
Innovation Solution
The leads of semiconductor devices are modified to have a reduced cross-sectional area along their longitudinal length, achieved through techniques like coining or slotting, which increases flexibility and reduces stress on the solder connections, thereby mitigating thermal expansion-induced cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the leads are made with uniform cross-sectional area, then the structural strength of the leads is maintained, but the solder connections crack under thermal fluctuations due to thermal expansion differences
Solution Approach 1:
The lead structure is modified with localized reduced cross-sectional areas (necking regions) at specific positions along the lead length. This creates non-uniform cross-sectional characteristics where certain regions have reduced area to accommodate thermal expansion differences, while other regions maintain full cross-sectional area to preserve structural strength and electrical conductivity.
Solution Approach 2:
The cross-sectional area parameter of the lead is changed along its length, creating a gradient or stepped structure. By varying the cross-sectional area parameter from the original uniform value to reduced values in specific regions, the lead can better accommodate thermal stress while maintaining overall structural integrity.
2Reliability
If the leads are made more flexible to reduce thermal stress, then the solder connection reliability improves, but the lead structural strength decreases
Solution Approach 1:
The lead is designed with localized flexibility regions (reduced cross-sectional areas) only where needed to accommodate thermal expansion, while the majority of the lead structure maintains full cross-sectional area and structural strength. This creates a differentiated structure with local flexibility without compromising overall strength.
Solution Approach 2:
The lead structure is segmented into regions of different cross-sectional areas - flexible regions with reduced area for stress accommodation, and rigid regions with full area for structural support. This segmentation allows different parts of the lead to serve different functions: flexibility where needed, strength where required.
3Reliability
If the leads are modified with reduced cross-sectional areas, then the thermal expansion stress on solder connections is reduced, but the manufacturing complexity increases
Solution Approach 1:
The cross-sectional area parameter of the lead is systematically varied along its length to create the necking structure. This parameter change can be achieved through standard manufacturing processes such as drawing, rolling, or stamping operations that can create non-uniform cross-sections, making the solution manufacturable despite the increased structural 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 modified leads with reduced cross-sectional areas significantly reduce stress on solder connections, minimizing crack formation and enhancing the reliability of electronic systems subjected to thermal changes, thus preventing malfunction or failure.
Implementation Method 1
The leads have a reduced cross-sectional area along a longitudinal length of the lead... which increases flexibility and reduces stress on the solder connections, thereby mitigating thermal expansion-induced cracking
Data Source
AI summary
An electronic device includes a semiconductor die, an enclosure, leads extending outwardly from the enclosure and electrically connected to the semiconductor die, and wherein the leads have a reduced cross-sectional area along a longitudinal length of the lead. The electronic device is designed to reduce the occurrence of crack formation between the leads and a printed circuit board.