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Process for High Density of Chip Terminals on Large Wafers

IP.com Disclosure Number: IPCOM000103990D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 1 page(s) / 25K

Publishing Venue

IBM

Related People

Farrar, PA: AUTHOR

Abstract

A lift-off process is used to define conventional bonding pads having good adhesion to substrate material and a solder wettable top surface. Next, vacuum deposition masking is used to define oversized solder pads overlapping their respective bonding pads. When solder is reflowed, it pulls back to edges of the bonding pads. Metals are selected to permit low deposition temperature (if necessary) in the lift-off process. This process permits use of masking material sufficiently thick to resist mask damage during separation from wafers. Solder is vacuum deposited through a mask having holes somewhat larger than the lift-off defined bonding pads. The very large number of small terminals on the large wafer requires that relatively thick deposition mask material (e.g., 0.

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Process for High Density of Chip Terminals on Large Wafers

      A lift-off process is used to define conventional bonding pads
having good adhesion to substrate material and a solder wettable top
surface.  Next, vacuum deposition masking is used to define oversized
solder pads overlapping their respective bonding pads.  When solder
is reflowed, it pulls back to edges of the bonding pads.  Metals are
selected to permit low deposition temperature (if necessary) in the
lift-off process.  This process permits use of masking material
sufficiently thick to resist mask damage during separation from
wafers.
     Solder is vacuum deposited through a mask having holes somewhat
larger than the lift-off defined bonding pads.  The very large number
of small terminals on the large wafer requires that relatively thick
deposition mask material (e.g., 0.005-inch-thick molybdenum) be used
to resist mechanical damage during wafer/mask separation after
deposition.  Reflowed solder pad volume is controlled by mask hole
size and deposition thickness.

Disclosed Anonymously.