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IMMERSION Sn/Pb PLATING BATH FOR TAB TAPE

IP.com Disclosure Number: IPCOM000006937D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-11
Document File: 1 page(s) / 52K

Publishing Venue

Motorola

Related People

George F. Carney: AUTHOR [+2]

Abstract

The majority of ASIC packages that ar being planned for future generations of the 0.5pm BiCMOS technol- ogy are in the TAB format due to the high pincount requirements. The only hvo lead fmish options currently available are Sn and Au. Both of these lead finishes have liabilities. The Sn has a tendency to grow whiskers, a single mono!iIament crystal whose growth rate is a func- tion of time and temperature. Whiskers on any elec- tronic part can cause long term reliability problems because the whiskers eventually can grow to an adja- cent lead and short the device. The Au lead finish increases unit costs and requires higher bonding forces that can potentially jeopardize barrier integrity. If immer- sion solder were offered the costs would remain low and the whisker problem could be eliminated. Currently there is no immersion solder system available from plat- ing bath manufacturers that can operate in the thin thick- ness ranges required for TAB tape.

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M-LA INC. Technical Developments Volume 19 June 1993

IMMERSION Sn/Pb PLATING BATH FOR TAB TAPE

by George F. Carney and Eric J. Woolsey

PROBLEM:

  The majority of ASIC packages that ar being planned for future generations of the 0.5pm BiCMOS technol- ogy are in the TAB format due to the high pincount requirements. The only hvo lead fmish options currently available are Sn and Au. Both of these lead finishes have liabilities. The Sn has a tendency to grow whiskers, a single mono!iIament crystal whose growth rate is a func- tion of time and temperature. Whiskers on any elec- tronic part can cause long term reliability problems because the whiskers eventually can grow to an adja- cent lead and short the device. The Au lead finish increases unit costs and requires higher bonding forces that can potentially jeopardize barrier integrity. If immer- sion solder were offered the costs would remain low and the whisker problem could be eliminated. Currently there is no immersion solder system available from plat- ing bath manufacturers that can operate in the thin thick- ness ranges required for TAB tape.

SOLUTION:

  Immersion tin plating compositions capable of pro- viding tin plate over copper surface are known and disclosed. It is also known that immersion tin plating compositions plate by displacement whereby theoreti- cally a mole of stannous tin displaces 2 moles of copper. Methane sulfonic acid was used as the base formulation and contained the soluable salts of Sn and Pb...