Leadframe Attach Portion With Through-Hole for Solder Joint Reliability
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Solution Overview
Problem
The existing lead frames in semiconductor packages face issues with solder joint reliability due to thermal expansion differences between the semiconductor package and external circuits, leading to cracks and potential electrical disconnection.
Innovation Solution
Incorporating an outer portion of the lead finger with a specific width, length, and thickness, featuring an opening that extends through its thickness, which is plated for enhanced solderability and includes a through-hole design to secure the solder joint, reducing the normal force acting on the solder joint and enhancing its durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional lead frame attach portion is used, then the structure is simple, but the solder joint reliability deteriorates due to cracks from thermal expansion differences
Solution Approach 1:
The attach portion is divided into multiple segments by introducing openings that extend through its thickness, creating a segmented structure. This segmentation allows the attach portion to better accommodate thermal expansion differences between the semiconductor package and external circuit, reducing stress concentration and preventing crack formation in the solder joint.
Solution Approach 2:
The attach portion incorporates openings (through-holes) that create a porous or hollow structure. This porous design provides compliance and flexibility to absorb thermal stress during temperature cycling, thereby improving solder joint reliability by preventing crack propagation while maintaining electrical connectivity.
2Strength
If the attach portion is made thicker to strengthen the solder joint, then the strength increases, but the normal force from thermal expansion increases cracks in the solder joint
Solution Approach 1:
By segmenting the attach portion through openings, the structure maintains adequate thickness for strength while creating compliance zones that reduce thermal stress transmission to the solder joint.
Solution Approach 2:
The openings change the mechanical parameters of the attach portion, reducing its effective stiffness and allowing it to better accommodate thermal expansion differences. This parameter change reduces the normal force transmitted to the solder joint during temperature cycling, preventing crack formation while maintaining structural integrity.
3Reliability
If openings are added to the attach portion, then the solder joint reliability improves, but the manufacturing complexity increases
Solution Approach 1:
The openings are integrated into the lead frame structure during manufacturing, segmenting the attach portion to improve reliability. The design allows for standard manufacturing techniques to create the openings, balancing the added complexity with significant reliability improvements.
Data Source
AI summary
A lead frame includes a die pad and a lead finger with an inner portion which is configured to be electrically connected to contact pads of a die and with an outer portion which has an attach portion. The attach portion is configured to be soldered to an external solder pad, wherein the attach portion has a width, a length and a thickness. An opening extends through the thickness of the attach portion.