Reflow Wall and Roughened Lead Frame for Semiconductor Adhesion
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Solution Overview
Problem
Packaged semiconductor devices often experience reliability failures due to poor adhesion between the molding compound and the lead frame, leading to delamination issues.
Innovation Solution
The implementation of a particle roughened surface on the lead frame and the formation of reflow walls surrounding the solder joints, which are created using polymeric materials and ink jet or screen printing techniques, enhances the adhesion between the molding compound and the lead frame, and restricts lateral solder reflow to form taller, more reliable solder joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a smooth lead frame surface is used, then the manufacturing process is simple, but the adhesion between molding compound and lead frame is poor
Solution Approach 1:
The lead frame surface is modified locally at specific positions (such as around solder joints or in designated adhesion zones) to create a roughened texture, while other areas remain smooth. This localized modification improves adhesion where needed without unnecessarily complicating the entire lead frame structure.
Solution Approach 2:
The lead frame surface is roughened during the lead frame manufacturing process itself, before the soldering and molding steps. This preliminary surface preparation ensures that when the molding compound is later applied, the adhesion interface is already optimized for strong bonding.
2Reliability
If reflow walls are formed using traditional methods, then the process is established, but the solder joint height and reliability are insufficient
Solution Approach 1:
The reflow wall formation process utilizes changes in material parameters during printing (such as viscosity, temperature, and curing characteristics) to achieve precise control over wall height and shape. By adjusting printing parameters like inkjet droplet size, screen mesh count, or curing temperature, the desired solder joint support structure is obtained.
Solution Approach 2:
Traditional mechanical methods for forming reflow walls (such as physical barriers or masks) are replaced with printing-based approaches (inkjet or screen printing) that deposit material directly in the desired pattern. This substitution allows for more precise and flexible reflow wall formation.
3Strength
If the solder joint height is increased, then the mechanical stress resistance improves, but the lateral solder reflow control becomes more difficult
Solution Approach 1:
The reflow wall structure is segmented into distinct regions with different heights or properties, allowing the solder joint to have increased height in areas needing mechanical strength while maintaining precise lateral control in areas requiring reflow management. The segmented structure guides solder flow vertically while preventing unwanted lateral spread.
Solution Approach 2:
The reflow wall is formed using composite material systems (such as polymer matrices with filler particles) that provide both the structural support for tall solder joints and the surface properties needed to control solder wetting and lateral reflow. The composite nature allows simultaneous optimization of mechanical support and fluid control.
Data Source
AI summary
A packaged semiconductor device includes a lead frame and a semiconductor device. A solder joint is coupled between the lead frame and a terminal on the semiconductor device. A reflow wall is on a portion of the lead frame and is in contact with the solder joint. A molding compound covers portions of the semiconductor device, the lead frame, the solder joint, and the reflow wall.