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 integrated circuits (ICs). The complete package is 650 μm thick including a 550 μm thick chip and a 100 μm 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 fiber push connection (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