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This article teaches an interconnection for gang bonding of semiconductor chips to preformed spiders which reduces or eliminates the electro-migration potential of gold-tin connected packages.
English (United States)
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Controlled Composition Gang Bond Chip Interconnection
This article teaches an interconnection for gang bonding of semiconductor
chips to preformed spiders which reduces or eliminates the electro-migration
potential of gold-tin connected packages.
It describes a method for confining tin, a required component on this type of
chip interconnection, by depositing the gold-tin materials such that during the
bonding of the pieces, alloying of the tin with gold occurs so as to leave no free
tin in the system. The desired alloy is initiated at 280 degrees C with a 30 atomic
weight tin and must be controlled to terminate at 418 degrees C with a tin-gold
alloy having 50 percent atomic tin. If the alloy contains more than 50 percent tin,
failures of interconnection bonds made with it will occur due to electromigration of
free tin in the alloy and corrosion related to entrapment of ionic residues.
A spider 10 is plated (11) with approximately 7500 angstroms of gold and
bonded to a semiconductor wafer 13 having an aluminum pad 14 thereon. This
pad is coated with a standard chrome copper gold coating 15 overlayed with a
13,000-angstrom layer 16 of gold and a 20,000-angstrom layer 17 of tin. Both
the gold layer 16 and tin layer 17 are preferably evaporated over the chrome
copper gold coating 15.
With this system, corrosion migration does not occur and fluxless reflow
soldering is accomplished at temperatures of 100 degrees below the thermal
compression bonding techniques known t...