Gate Insert Tool Curved Edge Reduces Mold Heel Cracks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mold heel cracks occur during the formation and high temperature reflow process of plastic ball grid arrays (PBGAs) due to high stress at the substrate, particularly at the injection site of the mold cap, caused by sharp corners and steep mold gate designs, leading to increased susceptibility to cracking.
Innovation Solution
A gate insert tool with a nozzle head featuring a chamfered contour outlining an inverted Sigmoid function curve is used to smooth the mold cap edge, reducing stress concentrations and eliminating sharp corners, thereby minimizing the likelihood of mold heel cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a steep mold gate insert design is used to facilitate mold cap formation, then the ease of manufacture is improved, but the stress concentration at the substrate increases causing micro cracks
Solution Approach 1:
The gate insert tool edge is designed with a contoured curved profile instead of a straight steep angle. The curve radius at the leading edge is specifically controlled to be between 0.002 to 0.006 inches, creating a rounded transition that eliminates sharp corners while maintaining the gate insert's ability to form the mold cap. This curvature distributes stress evenly across the substrate surface.
Solution Approach 2:
The invention changes the geometric parameters of the gate insert tool edge from a steep linear profile to a controlled curved profile with specific radius parameters. By adjusting the curve radius parameter within the specified range and controlling the angle of the contoured edge, the design optimizes both the mold cap formation capability and the stress distribution on the substrate.
2Strength
If high clamping pressure is applied during molding to ensure proper bonding, then the strength of the bond is improved, but the stress at the substrate increases likely to cause micro crack
Solution Approach 1:
The contoured curved edge of the gate insert tool creates a gradual transition zone that distributes the high clamping pressure over a larger area of the substrate. The curved profile prevents stress concentration at sharp corners, allowing high bonding pressure to be applied without creating micro cracks in the substrate.
3Manufacturing precision
If a sharp corner design is used at the mold heel to define the mold cap edge, then the manufacturing precision is improved, but the susceptibility to cracking increases
Solution Approach 1:
The gate insert tool edge is designed with a contoured curved profile that provides both precise mold cap edge definition and crack resistance. The specific curve radius parameters ensure the edge is sharp enough for manufacturing precision while rounded enough to prevent stress concentration and cracking.
Solution Approach 2:
The invention optimizes the geometric parameters of the gate insert edge, controlling the curve radius between 0.002 to 0.006 inches and the angle of the contoured edge. These parameter changes achieve the optimal balance between edge sharpness for precision and roundedness for crack resistance.
Data Source
AI summary
A semiconductor package is provided which addresses problems of mold cap heel cracking. The package may made by using a cavity die and a gate insertion tool. The gate insertion tool, which fits into the cavity die, has an elongated body and includes a nozzle head with an edge which is contoured in relation to a mold cap formed on a substrate. The edge defines a curved border, for the mold cap, from a plane above the substrate to a plane lying on the substrate. The nozzle head includes a slot, for admitting a cull runner tip, centered on an axis of the elongated body.