Raised Dam Pattern on Leadframe to Prevent Mold Flash
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Solution Overview
Problem
Mold flash occurs during the molding process of semiconductor packages due to the microstructure of the leadframe surface, leading to excess mold material bleeding out and causing quality and yield reduction issues, despite high clamp forces and existing deflashing processes.
Innovation Solution
A raised dam pattern with a different material than the dam bar or clip is implemented on the leadframe, which acts as a mold restraining dam to prevent mold flash by being taller than the mold flash height, typically formed using inkjet printing with materials like solder resist or low modulus epoxy, and positioned on the dam bar or top side clip to prevent mold material from bleeding beyond the mold outline.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high clamp force molding process is used to prevent mold flash, then mold material restraint is improved, but leadframe surface microstructure causes mold material to bleed out through pathways
Solution Approach 1:
The patent applies a raised dam pattern selectively at the mold outline location on the leadframe surface. This creates a localized barrier with different height and material properties (epoxy or solder resist coating) compared to the surrounding copper surface, providing enhanced restraint exactly where mold flash occurs without requiring increased clamp force across the entire mold cavity.
Solution Approach 2:
The raised dam pattern introduces a vertical dimension (height) to the otherwise planar leadframe surface. The dam protrudes upward by 0.5-2.0 mils to create a physical barrier that blocks the horizontal flow path of mold material, effectively adding a third dimension to prevent flash without increasing clamping pressure.
2Productivity
If unit density on leadframe strip is increased for cost reduction, then productivity is improved, but mold clamp force per unit decreases increasing risk of mold flash
Solution Approach 1:
The raised dam pattern provides localized reinforcement at the mold outline, allowing high unit density configurations where clamp force is distributed across multiple units. Each unit's dam structure independently prevents flash, enabling closer unit spacing without compromising flash prevention.
3Object-affected harmful factors
If deflashing process is used to remove excess mold material, then mold flash is removed, but loose mold flash material can cause lead contamination and quality issues
Solution Approach 1:
The raised dam pattern prevents mold flash from occurring in the first place by creating a physical barrier at the mold outline. This preliminary prevention eliminates the need for subsequent deflashing operations that could generate loose contaminant material, addressing the problem at its source rather than treating symptoms afterward.
Data Source
AI summary
A semiconductor package includes a semiconductor die including circuitry electrically coupled to bond pads that is mounted onto a leadframe. The leadframe includes a plurality of leads and a dam bar having a transverse portion that extends between adjoining ones of the leads. The bond pads are electrically connected to the plurality of leads. A raised dam pattern is on the dam bar or on an edge of an exposed portion of a top side clip of the semiconductor package that is positioned above and connects to the semiconductor die. The raised dam pattern includes a first material that is different relative to the material of the dam bar or the clip. A mold material encapsulates the semiconductor die.