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Low-cost Semiconductor QFN Package Providing Enhanced Thermal Management

IP.com Disclosure Number: IPCOM000010471D
Publication Date: 2002-Dec-05
Document File: 8 page(s) / 210K

Publishing Venue

The IP.com Prior Art Database

Abstract

Abstract A new structure for providing a low-cost QFN semiconductor package having enhanced thermal management wherein a semiconductor die is mounted in a quad flat no-lead [QFN] leadframe with die pad exposed upward away from the printed circuit board (PCB). The die pad is up set and exposed upward for ambient cooling when mounted on PCB. The tie bars on four corners anchor the die pad and the leads are also up set such that both die pad and leads are buried and secured well into package for package robustness. The spring action of the tie bars pushes and levels the die pad on top and the leads at the bottom, reducing or possibly eliminating the need for leadframe taping to minimize mold flash. The upset height is so designed such that the die surface will be on the same level or lower than the lead tips providing for a shorter wire span and less impedance, hence higher speed. Lower cost is achieved by reducing or possibly eliminating the leadframe tape, having a shorter wire span and the elimination of bake/dry pack.

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Low-cost Semiconductor QFN Package Providing

Enhanced Thermal Management

Abstract

A new structure for providing a low-cost QFN semiconductor package having enhanced thermal management wherein a semiconductor die is mounted in a quad flat no-lead [QFN] leadframe with die pad exposed upward away from the printed circuit board (PCB).  The die pad is up set and exposed upward for ambient cooling when mounted on PCB. 

The tie bars on four corners anchor the die pad and the leads are also up set such that both die pad and leads are buried and secured well into package for package robustness.  The spring action of the tie bars pushes and levels the die pad on top and the leads at the bottom, reducing or possibly eliminating the need for leadframe taping to minimize mold flash.  The upset height is so designed such that the die surface will be on the same level or lower than the lead tips providing for a shorter wire span and less impedance, hence higher speed.  Lower cost is achieved by reducing or possibly eliminating the leadframe tape, having a shorter wire span and the elimination of bake/dry pack.

Introduction

A standard quad flat pack no-lead (QFN) semiconductor package mounts on a printed circuit board (PCB) with the die pad exposed downward facing the PCB, thus a hot device can devitrify underlying PCB causing undesirable component and/or system failure.  Unfortunately, there are few low cost external heat spreader currently available in QFN packages which can aide in reducing heat conducted into the PCB. 

Another problem is that existing QFN packages require longer gold wire interconnects which produce a device having lower speed, and require a special loop profile to enable packages having very thin profile.  These special gold wire interconnects also require slow wire bonding techniques which are also prone to wire-to-die shorts.  To reduce shorts in the prior art, expensive additional processing like leadframe taping is used which unfortunately is prone to wrinkling and also limits clamping pressure/package compaction. 

Thus it would be desirable to make a semiconductor QFN package having improved thermal dissipation at a low cost while having high reliability and low profile.

Key Terms

QFN, SEMICONDUCTOR PACKAGE, SURFACE MOUNT, SOIC, TSSOP, QFP, LEADFRAME

Detailed Explanation of the Drawings

Referring to FIG.1, the die pad is up set and exposed upward for ambient cooling when mounted on PCB facilitating the mounting of external heat spreader for thermal performance enhancement and eliminating the devitrification of the underlying PCB.

This can also be applied to other surface mount packages like SOIC, TSSOP, QFP and the like with similar improvements in thermal performance.  The tie bars on four corners anchor the die pad and the leads are also up set such that both die pad and leads are buried and secured well into package for package robustness.  The spring action of the tie bars pushes and levels the die pad on top and the leads at t...