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Al Wires for Preventing Die Movement

IP.com Disclosure Number: IPCOM000234936D
Publication Date: 2014-Feb-17
Document File: 6 page(s) / 518K

Publishing Venue

The IP.com Prior Art Database

Abstract

Die rotation and off-center die placement issues exist in integrated circuit packages, such as Power Quad Flat No leads (PQFN) packages, after solder paste reflow in die bonding process because the solder paste boils and liquefies in the reflow oven. An off-center or rotated die will affect subsequent wire bond processes and ultimately, product quality. In this paper we present a method of preventing die rotation and movement after die bonding. The method includes adding Al wires on the lead frame flag at the four edges within which the die will be placed. The wires limit die rotation and movement during reflow. It also has been found that attaching Al wires on the lead frame flag can prevent resin bleed during a molding process, where the resin bleed was due to pad warpage. Adding Al wires on the lead frame flag edge before the die bond process can prevent pad warpage and thus avoid resin bleed due to the pad warpage.

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Al Wires for Preventing Die Movement

Abstract

Die rotation and off-center die placement issues exist in integrated circuit packages, such as Power Quad Flat No leads (PQFN) packages, after solder paste reflow in die bonding process because the solder paste boils and liquefies in the reflow oven.  An off-center or rotated die will affect subsequent wire bond processes and ultimately, product quality.  In this paper we present a method of preventing die rotation and movement after die bonding.  The method includes adding Al wires on the lead frame flag at the four edges within which the die will be placed.  The wires limit die rotation and movement during reflow.  It also has been found that attaching Al wires on the lead frame flag can prevent resin bleed during a molding process, where the resin bleed was due to pad warpage.  Adding Al wires on the lead frame flag edge before the die bond process can prevent pad warpage and thus avoid resin bleed due to the pad warpage.  

Introduction

Die rotation and off center die placement issues exist, such as on PQFN devices after solder paste reflow in the die bond process, which influence quality and stability on subsequent wire bonding processes. During solder paste reflow process, solder paste boils and liquefies in reflow oven so the die bonding on solder paste can rotate and move, which results in “die rotation” and “off-center die placement” issues.

Below, we present a method for preventing these issues from occurring.  The method includes adding Al wires on the lead frame flag at the four edges of the die attach position before dispensing solder paste during the die bond process. Current solder paste die bond process flow is to dispense solder paste, die bond on the solder paste and then reflow.  We propose adding Al wires, then solder paste dispense, die bonding, then reflow.  The four Al wires added to the lead frame limit die movement and die rotation that may occur during reflow.

Design and Implementation

Figure 1 shows the solder paste die bond process flow.  It includes solder paste dispensing, die bonding, and solder paste reflow.  After reflow, die rotation and die placement off center issue occurred as shown in Figure 1.

                                            

   

 
 

Figure 1.  Solder paste Die Bond process flow

 
 

Figure 2 shows our new process flow, which includes adding four Al wires on the lead frame flag, solder paste dispensing, die bonding, and solder paste reflow. The four Al wires prevent die rotation and off-center die placement issues.

                                     

Figure 2.  Solder paste Die Bond process flow for new design

 

Proof of concept

In order to prove the effectiveness of the above-described process, we prepared assembly samples that included four Al wires added to the lead frame flag as control lot.  Die rotation and off-center die placement data indicate th...