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Investigations of Laser Soldered TAB Inner Lead Contacts

Investigations of Laser Soldered TAB Inner Lead Contacts Tape Automated Bonding TAB is a modern technology which meets the requirements for microconnecting VLSI circuits. The limitations for gang bonding chips with high lead counts and reduced pitches are increased bond forces and induced mechanical stress. Laser soldering is an alternative for such contacts. Because microjoining of surfaces occurs via thermal energy from the laser beam, no mechanical pressure is necessary. Due to the optical properties of the laser beam and the possibility to reduce the laser spot, soldering of small pitches is possible. The results of TAB inner lead bonding with a pulsed NdYAG laser are presented. Tapes with three metallisations Sn, NiSn and Au were laser soldered to bumps consisting of gold and goldtin. The pull strength of laser soldered TABcontacts was optimised by variation of laser power and reliability investigations were performed. The metallurgy of laser soldering is different and more critical to long term reliability than that of gang bonded ILBcontacts, even if identical tape and bump materials are applied. An accumulation of eutectic 8020 AuSn solder in the bonded interface results in a strong degradation due to Kirkendall pore formation in the ternary CuSnAu system. The application of a tape with a diffusion barrier of Ni inhibits this effect. But during thermal ageing these contacts show a strong degradation of pull forces which is attributed to the formation of brittle intermetallic compounds of the elements Ni, Sn and Au in the contact area. Laser soldering of Auplated tapes to AuSn solder bumps is possible. The contacts show optimal pull forces and a minimal degradation after thermal ageing. This is attributed to the formation of an intermetallic compound with a high stability. The Zeta phase acts as a diffusion barrier between the copper lead and the eutectic AuSn solder. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Microelectronics International Emerald Publishing

Investigations of Laser Soldered TAB Inner Lead Contacts

Zakel, E.; Azdasht, G.; Reichl, H.
Microelectronics International , Volume 9 (1): 7 – Jan 1, 1992
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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
1356-5362
DOI
10.1108/eb044463
Publisher site
See Article on Publisher Site

Abstract

Tape Automated Bonding TAB is a modern technology which meets the requirements for microconnecting VLSI circuits. The limitations for gang bonding chips with high lead counts and reduced pitches are increased bond forces and induced mechanical stress. Laser soldering is an alternative for such contacts. Because microjoining of surfaces occurs via thermal energy from the laser beam, no mechanical pressure is necessary. Due to the optical properties of the laser beam and the possibility to reduce the laser spot, soldering of small pitches is possible. The results of TAB inner lead bonding with a pulsed NdYAG laser are presented. Tapes with three metallisations Sn, NiSn and Au were laser soldered to bumps consisting of gold and goldtin. The pull strength of laser soldered TABcontacts was optimised by variation of laser power and reliability investigations were performed. The metallurgy of laser soldering is different and more critical to long term reliability than that of gang bonded ILBcontacts, even if identical tape and bump materials are applied. An accumulation of eutectic 8020 AuSn solder in the bonded interface results in a strong degradation due to Kirkendall pore formation in the ternary CuSnAu system. The application of a tape with a diffusion barrier of Ni inhibits this effect. But during thermal ageing these contacts show a strong degradation of pull forces which is attributed to the formation of brittle intermetallic compounds of the elements Ni, Sn and Au in the contact area. Laser soldering of Auplated tapes to AuSn solder bumps is possible. The contacts show optimal pull forces and a minimal degradation after thermal ageing. This is attributed to the formation of an intermetallic compound with a high stability. The Zeta phase acts as a diffusion barrier between the copper lead and the eutectic AuSn solder.

Journal

Microelectronics International – Emerald Publishing

Published: Jan 1, 1992

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