Browse Prior Art Database

Sn Sputter Removal

IP.com Disclosure Number: IPCOM000121401D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 44K

Publishing Venue

IBM

Related People

Goldsmith, CC: AUTHOR [+4]

Abstract

This disclosure proposes to allow wirebonding on thin Au structures (500 to 2000 Angstroms) in the presence of Sn oxide. Currently wirebonding is performed on one micron Au structures which are fabricated using a dual Au evaporation technique, which is both expensive and time consuming. Before chips are joined to C4 pads, flux is first applied, followed by Pb/Sn solder bonded chips. Unfortunately, the flux and solder are not confined to the C4 pads. The flux runs out onto the ECs with the Sn tracking the flux. As a result a thin layer of Sn oxide will form after experiencing a thermal reflow subsequently hampering wire bonding. Bond windows are impacted with 1 mm of Au, but are severely impacted with thin Au. This is quite critical since there is a drive towards a uniform thin Au process.

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Sn Sputter Removal

      This disclosure proposes to allow wirebonding on thin Au
structures (500 to 2000 Angstroms) in the presence of Sn oxide.
Currently wirebonding is performed on one micron Au structures which
are fabricated using a dual Au evaporation technique, which is both
expensive and time consuming. Before chips are joined to C4 pads,
flux is first applied, followed by Pb/Sn solder bonded chips.
Unfortunately, the flux and solder are not confined to the C4 pads.
The flux runs out onto the ECs with the Sn tracking the flux.  As a
result a thin layer of Sn oxide will form after experiencing a
thermal reflow subsequently hampering wire bonding.  Bond windows are
impacted with 1 mm of Au, but are severely impacted with thin Au.
This is quite critical since there is a drive towards a uniform thin
Au process.

      In this disclosure, proposed is a very short but effective Rf
sputter cleaning using Ar ions.  Auger electron spectroscopy (AES)
has shown this thickness of Sn oxide to be about 20 Angstroms.  Upon
bonding a 500 Angstrom thin Au structure which had Sn oxide on the EC
pads, only a one-point bond window was found.  The part was given a
one-minute Rf sputter clean with no preheating of the substrate.  AES
revealed no Sn or Sn oxide present and an eleven-point wire bond
window was achieved.  Because Sn oxide cannot be reduced in forming
gas, it is essential to remove all of the Sn so that it does not
participate in any oxidation post thermal cyc...