Negative Lead Standoff in Molded Semiconductor Packages for Top-Side Cooling
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Solution Overview
Problem
Conventional molded semiconductor packages with positive lead standoffs result in high overall height tolerance, necessitating thicker thermal interface materials that increase thermal resistance in top-side cooling applications.
Innovation Solution
The design incorporates a negative lead standoff where the leads terminate outside the mold compound in a plane coplanar with or above the bottom surface, eliminating the lead height tolerance from the overall package height, allowing for a thinner thermal interface material and reduced thermal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a positive standoff is used between the leads and the bottom of the molded package body, then the leads are in the same plane or lower plane as the bottom of the molded package body, but the overall package height tolerance increases (up to 300 μm or greater)
Solution Approach 1:
The patent inverts the conventional positive standoff design by implementing a negative standoff where the bottom surfaces of the leads are coplanar with or above the bottom main surface of the mold compound. This inversion eliminates the lead height tolerance from the overall package height tolerance calculation, reducing the total tolerance from 300 μm or greater to approximately 100 μm or less.
2Reliability
If a thicker thermal interface material is used to compensate for the total height tolerance, then the package can accommodate the tolerance variation, but the thermal resistance of the thermal path increases
Solution Approach 1:
The patent changes the key parameter of lead standoff configuration from positive to negative, which directly enables the use of thinner thermal interface material (reducing thickness from typical 200-300 μm to 50-100 μm or less). This parameter change simultaneously improves thermal resistance while maintaining adequate contact reliability through the reduced but sufficient interface material thickness.
3Manufacturing precision
If the bottom surface of each lead is coplanar with or above the bottom main surface of the mold compound, then the lead height tolerance is eliminated from overall package height, but the leads must be bent downward outside the mold compound
Solution Approach 1:
The patent incorporates lead bending as a preliminary action during the lead formation process before package assembly. The leads are pre-bent to achieve the negative standoff configuration, which simplifies the overall manufacturing process by eliminating the need for post-assembly lead adjustment and ensures consistent coplanarity with the mold compound bottom surface.
Data Source
AI summary
A molded semiconductor package includes a mold compound, a plurality of leads each having a first end embedded in the mold compound and a second end protruding from a side face of the mold compound, and a semiconductor die embedded in the mold compound and electrically connected, within the mold compound, to the plurality of leads. The second end of each lead of the plurality of leads has a bottom surface facing in a same direction as a bottom main surface of the mold compound. Each lead of the plurality of leads has a negative standoff relative to the bottom main surface of the mold compound.