To provide a lead-free solder material which is easily made into foil and has excellent solderability at a temperature slightly over 300°C, and to provide a method of bonding wafers with each other with heat resistance and bonding strength equal to or more than those of a conventional solder material containing lead.
The fine powder of an Sn-Sb based or Sn-Ag based solder material not containing lead, a solvent such as isopropyl alcohol with weak polarity and a hydrocarbon compound such as succinic acid which is soluble in the solvent and has a carboxyl group (-COOH) at one end are mixed and turned to a slurry state, and it is applied to a wafer surface as the lead-free solder material by a spin coating method, a blowing method, a roller application method, a printing method or the like. Then, a plurality of wafers are stacked, heated while being pressed and soldered, thereby the heat resistance is improved. Further, they are heated again while being pressurized, a solder bonding layer is made into an alloy, and thereby the heat resistance and the bonding strength are improved.
COPYRIGHT: (C)2009,JPO&INPIT
Fukiaki Hiroaki
Kuboyama Takahiro
Kazuyuki Makita
Mitsuo Yamashita
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