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Method to Increase Number of Leads

IP.com Disclosure Number: IPCOM000240493D
Publication Date: 2015-Feb-03
Document File: 4 page(s) / 614K

Publishing Venue

The IP.com Prior Art Database

Abstract

The QFN package is very mature now. In this paper, we present a method for increasing the number of leads for a xQFN package by using a modified lead frame yet maintaining a small package size. The method does not add any complicated processes to current array xQFN assembly, such as half cut, selective plating and L/F etching.

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Method to Increase Number of Leads

Abstract

The QFN package is very mature now.  In this paper, we present a method for increasing the number of leads for a xQFN package by using a modified lead frame yet maintaining a small package size.  The method does not add any complicated processes to current array xQFN assembly, such as half cut, selective plating and L/F etching.

Introduction

We increase the number of leads of xQFN package by modifying the lead frame but at the same time, maintain a small package size.  We do not require any additional complicated process steps, such as half cut, selective plating and L/F etching.  The key features are:

                1. Lead frame with multiple rows of leads as shown in Fig, 1. The connecting of leads is the same as before, except that every other lead has a longer connect bar.  The longer connect bar should be formed as shown in Fig. 2.

                                            

              Figure 1. Top view of lead frame                      Figure 2. Perspective view of connection bars              

2. The lead frame pitch can be much smaller than current spec because the formed longer connect bar is in the different space with lead and will not influence the function of closed lead.

3. Proceed assembly as usual. In molding process, the mold cap must be higher than the connecting bar height.

4. When the strip is cut into units, all the lead connections will be isolated.

Design and Implementation

The important components of the assembly process are described below.

1. Lead frame manufacture can be done at supplier site. The formation of connecting bar can be done after etching/stamping process, as shown in Fig. 3.

Figure 3. Longer connection bar forming steps

2. Proceed assembly as usual. Cro...