Mold Cap Extensions for Semiconductor Package Cracking
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Solution Overview
Problem
Integrated circuit packages, particularly BGA and PBGA, face issues with solder mask cracking at chamfered corners due to exposure, leading to potential damage during handling, especially in larger sizes.
Innovation Solution
The introduction of extensions from the chamfered corners of the mold cap, which cover a greater area of the solder mask, reducing the risk of cracking by providing additional protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If chamfered corners are used on the mold cap, then moisture intrusion is prevented, but the solder mask becomes exposed and susceptible to cracking
Solution Approach 1:
The mold cap is segmented into two distinct functional zones: the main body with chamfered corners for moisture prevention, and extensions protruding from the chamfered surfaces that provide additional coverage. This segmentation allows each zone to perform its specific function independently - the chamfered body prevents moisture intrusion while the extensions protect the solder mask at corners and edges
Solution Approach 2:
The extensions are strategically positioned only at specific locations (corners and edges) where solder mask exposure occurs, rather than covering the entire mold cap. This local quality approach provides targeted protection exactly where needed - at the vulnerable corner and edge regions - while maintaining the moisture-preventing chamfered design in other areas
2Quantity of substance
If larger size packages are used to meet high-density connection needs, then more external electrical connections are available, but the solder mask becomes even more susceptible to cracking
Solution Approach 1:
The protection approach transitions from a two-dimensional surface coating (solder mask) to a three-dimensional structural solution (mold cap extensions). The extensions protrude vertically from the mold cap surface, creating a physical barrier that extends into the space above the solder mask, providing robust protection against mechanical stress and cracking in larger packages
Data Source
AI summary
A semiconductor package has a substrate with a solder mask layer, and upper and lower surfaces. Conductive traces and electrical contacts are formed on the substrate, and vias are formed in the substrate to electrically connect the conductive traces and electrical contacts. A semiconductor die is attached on the upper surface of the substrate. A mold cap is formed on the upper surface of the substrate and covers the die and the conductive traces. The mold cap includes a mold body having clipped corners and extensions that extend from each of the clipped corners. The extensions and clipped corners help prevent package cracking.