Lead-Frame Lead Structure for Thermal Stress-Resilient Solder Joints
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Solution Overview
Problem
Existing lead-frame packages face challenges in maintaining reliable electrical connections and resilience to temperature changes, particularly in harsh environments, due to stress on solder joints caused by expansion and compression of components.
Innovation Solution
The conductive leads are designed with a vertically bent distal end and recesses to provide flexibility and resilience, featuring a solder wettable surface for improved adhesion and insulation from the die pad, allowing the package to flex and maintain connections in extreme conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conductive lead is made rigid to ensure stable electrical connection, then the electrical connection stability is improved, but the package cannot withstand stress from thermal expansion and contraction
Solution Approach 1:
The conductive lead is designed with a bent configuration featuring a curve radius, transforming it from a rigid straight structure to a dynamic flexible structure. This bent shape allows the lead to flex and absorb thermal expansion/contraction stresses while maintaining electrical connection stability, resolving the contradiction between rigidity and thermal resilience.
Solution Approach 2:
The patent modifies the geometric parameters of the conductive lead by introducing a bent configuration with specific curve radius. This parameter change enables the lead to possess both structural stability for electrical connection and flexibility for thermal stress accommodation, simultaneously achieving connection reliability and temperature adaptability.
2Reliability
If the distal end of the conductive lead is extended beyond the package perimeter to provide external connection, then the electrical connectivity is improved, but the solder joint becomes more vulnerable to stress
Solution Approach 1:
The extended distal end is configured with a bent shape rather than a straight extension. This dynamic curved configuration allows the solder joint to flex with thermal expansion and contraction, reducing stress concentration and improving solder joint durability while maintaining electrical connectivity.
Solution Approach 2:
The bent configuration of the extended distal end acts as a pre-designed stress absorption mechanism. The curve radius provides a cushioning effect that anticipates and mitigates thermal stresses before they reach the solder joint, protecting it from damage while maintaining electrical connection.
3Object-affected harmful factors
If the conductive lead is fully enclosed by molding material for protection, then the environmental protection is improved, but the solder wettable surface cannot be accessed for connection
Solution Approach 1:
The solder wettable surface is extracted from the enclosed molding material by extending the distal end of the conductive lead beyond the package perimeter. This allows the soldering operation to access the wettable surface while the proximal end remains protected by the molding material, resolving the contradiction between environmental protection and soldering accessibility.
Solution Approach 2:
The conductive lead extends in a different spatial dimension (beyond the package perimeter) to expose the solder wettable surface. This dimensional arrangement allows the soldering interface to be accessible while the protected portion remains enclosed, simultaneously achieving environmental protection and soldering ease.
4Reliability
If the conductive lead has a large cross-section to reduce resistance, then the electrical conductivity is improved, but the package footprint increases
Solution Approach 1:
The conductive lead is designed with varying cross-sectional dimensions along its length. The proximal end near the semiconductor IC has sufficient cross-section for low resistance, while the extended distal end has reduced cross-section. This local quality variation maintains electrical conductivity where needed while minimizing overall package footprint.
Solution Approach 2:
The conductive lead is segmented into different functional zones: a proximal section with larger cross-section for electrical connection and a distal extended section with smaller cross-section for soldering. This segmentation allows optimization of conductivity in the critical area while reducing footprint in the extension area.
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 enhances the reliability of semiconductor ICs by ensuring durable electrical connections and reduces the package's footprint, while enabling efficient manufacturing through strip panel molding.
Implementation Method 1
a solder wettable surface of the conductive lead is exposed in a lateral direction
Data Source
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AI summary
An example lead-frame package, a method of manufacturing a lead-frame package, and an electrical system comprising a lead-frame package with improved conductive lead structure are provided. An example lead-frame package includes a semiconductor IC thermally coupled to a die pad. Molding material encloses the semiconductor IC defining a perimeter of the lead-frame package. A conductive lead is electrically connected to the semiconductor IC and exposed at a surface of the lead-frame package, the conductive lead having a proximal end and a distal end. The distal end of the conductive lead extends beyond the perimeter of the lead-frame package, the distal end bent vertically such that a solder wettable surface of the conductive lead is exposed in a lateral direction. The molding material further insulates the conductive lead from the die pad. A conductive lead recess is defined between the proximal end of the conductive lead and the die pad.