Segmented Plunger Runner Geometry for Semiconductor Molding Cull Reduction
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Solution Overview
Problem
The existing transfer molding process for semiconductor devices results in significant waste of molding compound due to the formation of a cull portion, which is not fully eliminated by previous solutions like the compressible mold plunger, as substantial compound remains between the plunger and mold recess even under maximum pressure.
Innovation Solution
A plunger assembly with a supplementary inner plunger and a biasing element is used, where the width of the runner at the opening connecting it to the mold supply pot is smaller than the main plunger, allowing the inner plunger to force compound into the runner without creating a cull portion, thereby reducing waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a compressible mold plunger with movable piston and spring is used to reduce cull space, then cull space is reduced, but substantial molding compound remains between the plunger and mold recess even under maximum pressure, preventing total elimination of cull
Solution Approach 1:
The plunger is segmented into two distinct parts: a main plunger and an inner plunger. The main plunger has a first end that contacts the molding compound, while the inner plunger has a second end that extends beyond the first end and also contacts the molding compound. This segmentation allows the inner plunger to push the molding compound into the runner more effectively, eliminating the cull portion that remains when using a single plunger design.
Solution Approach 2:
The inner plunger extends in the longitudinal dimension beyond the main plunger, creating a stepped configuration. This dimensional extension allows the inner plunger to reach further into the runner opening and completely eliminate the cull portion by pushing the molding compound directly into the runner, whereas the main plunger alone cannot achieve complete elimination due to the gap between its end and the mold recess.
2Loss of substance
If the runner width at the opening is made smaller than the main plunger width, then the inner plunger can force compound into the runner without creating cull portion, but the plunger assembly design becomes more complex
Solution Approach 1:
The inner plunger is nested within the main plunger, with the inner plunger positioned inside the hollow interior of the main plunger. This nesting arrangement allows the two-plunger system to function as a unified assembly that fits within the existing mold supply pot infrastructure. The inner plunger can extend beyond the main plunger to perform its specific function of pushing compound into the runner, while the overall assembly maintains a compact, integrated structure that does not significantly increase device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively minimizes the cull portion formation, leading to a 15% reduction in total molding compound consumption per mold shot and eliminates the need for manual cleaning, enhancing the efficiency and cost-effectiveness of the molding process.
Implementation Method 1
a biasing element, such as a spring, operative to maintain contact between the inner plunger and the molding compound
Data Source
AI summary
An apparatus and process are provided for molding electronic devices in a mold, which apparatus comprises at least one runner in the mold connected to a mold supply pot for channeling a molding compound from the mold supply pot to the electronic devices. A plunger assembly is also provided that comprises a main body, and a supplementary body configured to be movable relative to the main body. The plunger assembly is locatable in the mold supply pot and is drivable in a direction towards the runner for forcing the molding compound into the runner. In order to avoid or reduce cull formation, a width of the runner at an opening connecting the runner to the mold supply pot is smaller than a width of the main body of the plunger assembly.