Lead-Free Soldering in Microelectronics
Aleš Čeněk s.r.o.
The aim of this work is to provide the ingredients for understanding together with
knowledge of the implementation of lead-free solder alloys, soldering technology
and reliability in interconnection technology. Many of the lower melting point
solders have precious elements, whereas some of the inexpensive alternatives
wet poorly, are prone to oxidation during soldering and tend to corrode. The main
candidate can be SnCu, SnAg, SnAgCu, solders system with small amount of
Bi and In. During soldering, some of the metal substrate is dissolved into the
molten solder. As a result, the solder becomes supersaturated with the dissolved
metal and a layer of an intermetallic compound is formed at the metal-solder
interface. The intermetallic layer continues to grow after solidifi cation due to
thermally activated solid state diffusion mechanisms. The formation and growth
of intermetallic at the solder-substrate interface affect the solderability and
reliability of electronic solder joints.
In the present work, the kinetics of intermetallic phase formation between Cu
substrate and Sn1.5Ag0.7Cu9.5In solder alloy is studied and compared to SnAgCu
and SnAgCuBi solders. Sn1.5Ag0.7Cu9.5In alloy is a candidate material for leadfree
soldering at temperatures close to 200 °C due to signifi cant amount. The
excessive intermetallic phase formation may lead to a premature degradation of
the working solder joint. Bismuth decreases the rate of Cu3Sn layer formation.
The effect of indium on the intermetallic layer formation is two-fold. First is to
decrease the rate of Cu3Sn layer formation and the second is to increase the rate
of Cu6(Sn,In)5 layer formation.
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