Lead Frame Strip with Elongated Apertures for Degating Warpage Control
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Solution Overview
Problem
The existing degating processes for removing excess mold compound from semiconductor IC devices often result in mold compound adhesion to the lead frame, causing twisting or warpage of the lead frame strip, which can lead to assembly issues during packaging.
Innovation Solution
The use of lead frame strips with punch degating apertures in the side rails, where the total aperture length is greater than or equal to the die pad length, significantly reduces the contact area between the mold compound and the lead frame, allowing for easier removal of cull runners without causing warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional circular apertures are used in side rails for degating, then the lead frame strip can be easily manufactured, but the mold compound adheres strongly to the lead frame surface causing warpage during degating
Solution Approach 1:
The patent changes the geometric parameters of the apertures from conventional small circular shapes to elongated rectangular shapes with lengths greater than or equal to the die pad length. This parameter change increases the total aperture length along the first direction, which reduces the contact area between mold compound and lead frame in the degating region, thereby eliminating warpage while maintaining manufacturing feasibility
Solution Approach 2:
The patent transitions from circular apertures (one-dimensional measure of diameter) to rectangular apertures with significant length along the first direction (multi-dimensional measure). By making the aperture length comparable to or greater than the die pad length, the solution addresses the adhesion problem in a new dimensional approach, reducing mold compound contact area without compromising manufacturing ease
2Reliability
If the adhesion between mold compound and lead frame is increased for zero delamination products, then the encapsulation integrity is improved, but the lead frame strip cannot be automatically removed from the degater assembly requiring manual intervention
Solution Approach 1:
The patent applies local quality by creating distinct regions with different aperture characteristics. The elongated rectangular apertures are specifically positioned and dimensioned in the degating region to reduce mold compound contact area, while other regions of the lead frame maintain their normal structure. This localized modification allows automatic removal in the degating region without compromising encapsulation integrity elsewhere
Solution Approach 2:
The patent segments the lead frame strip into regions with different aperture characteristics. By providing elongated rectangular apertures specifically in the side rails for degating, it creates a segmented structure where the degating region has reduced adhesion for automatic removal, while other regions maintain full encapsulation integrity
3Manufacturing precision
If degate punchers push through cull runners with high adhesion, then complete severing is achieved, but the lead frame strip twists and bends causing permanent warpage
Solution Approach 1:
The patent extracts the mold compound from the degating region by designing elongated rectangular apertures that reduce the contact area between mold compound and lead frame. By removing or reducing the adhesive interface in the degating region, the solution allows complete severing of cull runners without the twisting and bending that causes warpage, while maintaining encapsulation integrity in non-degating regions
Data Source
AI summary
A lead frame strip includes an array of sites arranged in at least one row connected to two exterior side rails which traverse the lead frame strip on two opposite sides. Each of the sites is further connected to the two exterior side rails by subrails which extend between the two exterior side rails. Interior side rails extend between the subrails having a length dimension oriented along a first direction. The interior side rails include at least one punch degating aperture having an aperture length oriented along the first direction, wherein a total of the aperture length along the interior side rails is greater than or equal to the die pad length.