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QFN Lead Frame Design

IP.com Disclosure Number: IPCOM000234814D
Publication Date: 2014-Feb-07
Document File: 4 page(s) / 292K

Publishing Venue

The IP.com Prior Art Database

Abstract

With the industry trend moving towards miniaturization on QFN packages, the use of small die poses challenges in assembly processes. This paper describes a flexible QFN lead frame design that enables assembling QFN packages with extremely small die by reducing wafer saw and die bond difficulties. The QFN lead frame design can also be used to build dual or quad devices in a single lead frame, which enables MCM (Multi-Chip-Module).

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QFN Lead Frame Design

Abstract

With the industry trend moving towards miniaturization on QFN packages, the use of small die poses challenges in assembly processes. This paper describes a flexible QFN lead frame design that enables assembling QFN packages with extremely small die by reducing wafer saw and die bond difficulties. The QFN lead frame design can also be used to build dual or quad devices in a single lead frame, which enables MCM (Multi-Chip-Module).

Introduction

QFN package has become a common package type that connects ICs to the surfaces of PCBs since it uses perimeter I/O pads. In addition, the exposed copper die-pad technology also offers good thermal and electrical performance. However, with the PCB industry trend seeking further miniaturization and reduced costs, QFN suppliers are being driven to reduce size and increase component density on circuit boards.  In this paper we present a QFN lead frame design that will enable QFN suppliers to assemble very small QFN packages with the combined effort from wafer fab.  The QFN lead frame design also enables QFN supplier to build very small MCM (Multi-Chip-Module).

Design and Implementation

Figure 1 shows the structure of the lead frame and wafer designs.  We use a “pizza mask” wafer with multiple devices on a single wafer and die bond it on the QFN lead frame with multiple units design. The width of both die saw street and package saw street are the same.

Figure 1:  Lead frame and Wafer Design

Figure 2 shows an enlarged view of the pizza mask wafer before and after wafer dicing. Standard wafer dicing is applied on the wafer saw street to singulate the die design A & B, which is segregated by the grey colour line.

Figure 2: Pizza Mask Wafer Before & After Wafe...