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Mar 23rd, 2011
Fujitsu low temp copper thermocompression bonding
At the recent IMAPS Device Packaging Conference held in Ft McDowell AZ, Taiji Sakai of Fujitsu presented their new Cu-Cu thermo-compression bonding technology which uses “machined” bumps to achieve a significantly lower monolithic bonding temperature.
In order to achieve tighter pitch for high I/O devices, many device manufacturers are moving to copper pillar bumping where the copper is bonded by a Sn/Ag solder cap. [Ref]
The machined bumps reveal an amorphous like layer which allows surface recrystallization to produce a monolithic interface at significantly lower temperatures. When test structures were bonded at 200, 250 ˚C (for 30 min under 300 MPa pressure), and then compared to cmp’ed structures for shear strength and bulk fracture mode one can see the advantages of the machined surfaces.
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