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LEAD FRAME DESIGN FOR FINE PITCH WIRE BONDING

IP.com Disclosure Number: IPCOM000006727D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2002-Jan-25
Document File: 2 page(s) / 125K

Publishing Venue

Motorola

Related People

John Baird: AUTHOR

Abstract

High lead count IC packages require tine pitch wire bonding. The design and processing of a blanked or etched lead frame for a quad flat pack is presented that gives the required wire post pitch, and adequate lead-to- lead clearance. A lead frame design for tine pitch wire bonding is shown in Figure 1 and 2, attached.

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MOIOROLA /NC. Technical Developments Volume 18 March 1993

LEAD FRAME DESIGN FOR FINE PITCH WIRE BONDING

by John Baird

INTRODUCTION

  High lead count IC packages require tine pitch wire bonding. The design and processing of a blanked or etched lead frame for a quad flat pack is presented that gives the required wire post pitch, and adequate lead-to- lead clearance. A lead frame design for tine pitch wire bonding is shown in Figure 1 and 2, attached.

SUMMARY

  The bond pad spacing on the silicon die is 0.106 mm as a current target minimum. To keep the wires short, the pitch of the lead frame elements at the wire bond will be 0.145 mm. There is a practical lower liiit to this pitch using etched or blanked metal lead frames with about 0.150 mm thickness. Keeping the lead cross section at the tip nearly square, which is advantageous for stability during wire bonding, the wire post pitch then can be 0.150 with no clearance behveen leads. Clear- ance between leads is necessary for manufacturing the planform dimensions of the lead frame. Blanking will require about l/10 of the thickness for space between leads; etching will require about 6/10 of the thickness between the leads.

  Packages exist where lead spacing at the wire post bond requirements are met using printed circuit boards laminated to etched lead frames. Electrical connection to the etched lead frame from the printed circuit board is made by plating holes drilled through metal on the circuit board and the lead frame. The spacing and struc- tural requirements at the wire post arc met using photo patterned etched/plated traces on the PC board. Processing of this design is complex, expensive, and in current practice has a high fault rate.

  An alternative is using a conventional blanked or etched lead fiame where lead-to-lead separation is gained by down set forming every other lead giving a vertical separation. Practical use of the concept requires a par- ticular clamping method for the leads during wire bonding.

0 Motorola. inc. 1993

  The design presented is summarized in Figure 1. This uses limit pitch for die bonds and external leads. It is a 40 mm square quad flat pack with 416 leads. Lead- to-lead spacing is developed by forming alternate leads down to give a 0.114 mm vertical spacing. Forming gives this clearance from the lead at mid length where it is stabilized using Kapton or equivalent tape. The lead cross section at the tip has a width that is 0.78 times the height for the blanked (not etched) lead frame.

In Figure 1 the wire bond pad spacing on the die is
.106 mm, the wire bond spacing on the lead frame is ,145 mm, and before forming alternate leads down, the lead to lead spacing is .02 mm. After down set forming the alternate leads, the lead to lead vertical spacing is ,114 mm. The blanked form prior to down setting the leads allows for the longer path of the down set lead. As an alter...