Mold Chase Tooling for IC Lead Frame Tin Migration
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Solution Overview
Problem
During highly accelerated stress testing (HAST) of MaxQFP packages, tin in the plating layer can migrate and form undesirable conductive paths between adjacent leads due to insufficient metal-to-metal distance.
Innovation Solution
The manufacturing process involves designing tooling to allow molding compound to extrude along the proximal ends of the leads, increasing the metal-to-metal distance between adjacent leads, thereby reducing the likelihood of tin migration and conductive path formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the metal-to-metal distance between adjacent leads is reduced to increase lead density, then the productivity and compactness of the IC package is improved, but the reliability deteriorates due to tin migration and conductive path formation during HAST testing
Solution Approach 1:
The patent introduces molding compound as an intermediary material between adjacent leads. This compound fills the space between leads and creates a physical barrier that prevents tin migration and conductive path formation, thereby maintaining reliability while allowing reduced metal-to-metal distance for higher lead density
Solution Approach 2:
The patent uses a sacrificial spacer structure during the molding process that is temporarily present to maintain lead spacing, but is subsequently removed or dissolved. This allows precise control of metal-to-metal distance during manufacturing without permanent structural complexity
2Reliability
If the metal-to-metal distance between adjacent leads is increased to prevent tin migration, then the reliability is improved, but the lead density and productivity deteriorate
Solution Approach 1:
The patent transitions from controlling lead spacing in a single plane to utilizing three-dimensional space by having molding compound extrude along the length of leads and fill inter-lead spaces. This vertical/dimensional approach to spacing allows compact planar layout while maintaining adequate isolation distances through depth
3Device complexity
If standard molding tooling is used without lead-specific openings, then the device complexity is reduced, but the manufacturing precision deteriorates because molding compound cannot extrude along lead proximal ends to provide adequate spacing
Solution Approach 1:
The patent segments the molding tooling into lead-specific regions with dedicated openings and standard regions. Each lead proximal end area has a customized opening configuration that allows molding compound to extrude precisely where needed, while other areas use standard molding processes, balancing complexity and precision
Data Source
AI summary
A mold chase has first and second mold clamps having corresponding teeth and recesses configured such that, when the mold chase is closed onto a sub-assembly having an IC die mounted onto and wire-bonded to a lead frame, there are gaps between the recesses and the leads of the lead frame that allow molding compound to extend along opposing sides of proximal ends of the leads to increase the metal-to-metal distance between adjacent leads, thereby reducing the chances of, for example, tin migrating during HAST testing to form undesirable conduction paths between adjacent leads. In some embodiments, the mold clamp teeth have chamfered edges that are tapered at the mold chase cavity to form wedge-shaped gaps that allow the molding compound to extrude along the proximal ends of the leads of MaxQFP packages having two levels of “J” leads and gullwing leads.