Paul Kasulke

Fluxless die bonding of high power laser bars using the AuSn-metallurgy

This paper presents a new concept for a fluxless package design for commercial high power laser bars. The laser bars are soldered on CuW heatsinks using Au(80)Sn(20) solder. Then a Cu lead is bonded with the FPC method (Fiber-Push-Connection) as a cap and electrical contact. Finally, the heatsink is mounted on a Cu microchannel cooler with Pb(37)Sn(63). We describe the mounting processes in detail, showing the large bonding window for soldering with Au(80)Sn(20), which is necessary for industrial production. The metallurgy of the Au(80)Sn(20) bonding interface is not dependent on the bond parameters in the area of the bonding window. Electro-optical characterizations show excellent performance of the laser bars. An accelerated aging test gives a first indicator of the high reliability of this package concept.

A new approach to chip size package using meniscus soldering and FPC-bonding

A Chip Size Package was developed using a tape carrier for interconnection and redistribution of the pads of high pincount ICs. The complete package is 650 /spl mu/m thick including a 550 /spl mu/m thick chip and a 100 /spl mu/m thick flexible carrier. A three layer tape with gold or gold/nickel surface finish on the copper layer was used as flexible interposer. The production line which was established includes a low cost bumping on wafer level. The chips were provided with electroless Ni bumps on which a layer of eutectic Au-Sn solder was deposited by meniscus soldering. The bonding of these bumps to the flexible substrate was performed by FPC technology, a laser bonding method. Mechanical stability between the tape and the chip was achieved by application of a low stress adhesive prior to bonding. In a last step solder balls were placed on the tape and reflowed using a novel solder ball placement machine with an incorporated laser reflow unit. The package obtained is fully surface mount compatible, allowing easy processability.