QFN Lead Frame Trenches for Solder Void Heat Dissipation
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Solution Overview
Problem
Conventional Quad Flat Non-leaded (QFN) and Quad Flat Package (QFP) semiconductor packages face thermal dissipation issues due to voids generated during the soldering process, which hinder effective heat management despite using larger die pads.
Innovation Solution
The QFN package design incorporates a lead frame with a die pad having protrusions, trenches, and moats, where the molding compound fills spaces between the leads and die pad, and the trenches extend across protrusions to the moat, preventing void formation and enhancing thermal dissipation by allowing flux voids to escape during soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a big die pad area is used to improve thermal dissipation, then the thermal dissipation area is increased, but voids are generated during soldering that reduce thermal performance
Solution Approach 1:
The die pad is segmented by introducing multiple trenches that divide the continuous die pad structure into separate regions. These trenches create pathways for flux voids to escape during soldering while maintaining sufficient thermal contact area between the semiconductor die and the die pad, thus resolving the contradiction between large die pad area and void formation.
Solution Approach 2:
The trenches act as intermediary structures that facilitate the escape of flux voids during the soldering process. By providing these intermediate pathways, the trenches enable voids to be expelled from beneath the die pad without compromising the overall thermal dissipation capability of the enlarged die pad structure.
2Ease of manufacture
If conventional QFN package structure is used, then manufacturing is simple, but voids form during soldering that seriously reduce thermal dissipation
Solution Approach 1:
The die pad structure is segmented by introducing trenches that create separate regions. This segmentation is achieved through standard semiconductor manufacturing processes, maintaining ease of manufacture while effectively preventing void accumulation during soldering and improving thermal dissipation performance.
Solution Approach 2:
The physical structure of the die pad is changed by introducing trenches with specific dimensions and patterns. This parameter change in the die pad geometry enables flux voids to escape during soldering without significantly complicating the manufacturing process, thus improving thermal dissipation while maintaining manufacturing simplicity.
3Reliability
If mold compound fills all spaces between leads and die pad, then electrical isolation is improved, but voids trap heat reducing thermal dissipation
Solution Approach 1:
The die pad is segmented by trenches that allow mold compound to fill around the protrusions while maintaining thermal pathways. The trenches create a structured interface between the die pad and mold compound that ensures both electrical isolation through complete filling and thermal dissipation through controlled thermal contact areas.
Solution Approach 2:
The interface between the die pad and mold compound is given local quality variations through the trench structure. The protrusions and trenches create regions with different thermal and electrical properties, allowing optimal electrical isolation in filled regions while maintaining thermal dissipation pathways through the structured interface.
Data Source
AI summary
A Quad Flat No-Lead (QFN) package comprises a semiconductor die, a lead frame and molding compound. The lead frame comprises a die pad having a substantially rectangular inner part and a plurality of protrusions around the periphery thereof and contiguous therewith and extending outwardly therefrom, and a plurality of leads around the four sides of the die-pad. The molding compound encapsulates the semiconductor die and forming the package. The molding compound has a respective moat therein between each side of the die pad and a respective set of leads. The die pad has a plurality of trenches extending from the second surface of the die pad towards the first surface at least in the inner part of the die pad. The plurality of the trenches each extend across a protrusion to the moat.