Effect of cryogenic treatment prior to equal channel angular press (ecap) of sac solder
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Date
2018-05
Authors
Koay, Tze Yen
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Abstract
The SAC solder alloy has been proposed as the alternative solder to overcome the
environmental concern of lead (Pb-Sn) solder. Many researchers have studied the SAC
solder alloy and found that reliability issues of solder on mechanical properties such as
hardness and strength. The present work aims to look at how grain refinement influenced
the mechanical properties of a commercial SAC 305 solder alloy. In this work, SAC 305
solder were subjected to severe plastic deformation applied via Equal Channel Angular
Pressing (ECAP) which was conducted through route BC. Prior to ECAP, the solder alloy
was dipped in liquid nitrogen for cryogenic treatment. It is believed that cryogenic
treatment (CT) can improve the microstructure and performance of solder. The effect of
the dipping time of samples in liquid nitrogen and number of passes through ECAP
employed during pressing on hardness was studied. Elemental analysis of casted solder
alloy was analysed using XRF and it showed correct composition of SAC 305. Phases
and crystallite size of all the solders were examined by XRD and sample with cryogenic
treatment prior to ECAP exhibited a smaller crystallite size. Solder alloy with dipping in
liquid nitrogen prior to ECAP enhanced the Vickers microhardness of bulk solder alloy.
This is due to the microstructure of solder alloys with dipping of liquid nitrogen prior to
ECAP showed evidence of grain refinement as observed using Scanning electron
microscope (SEM). Besides, CT prior to ECAP improved the spreading and wetting angle
of reflowed solder on Cu substarate. For the mechanical properties, solder joint samples
with dipping in liquid nitrogen for shortest time of 10 minutes prior to ECAP gave the
highest shear strength through single lap joint test and the fracture surface showed smaller dimples compared to others. In conclusion, grain refinement and mechanical properties
of solder alloy improved through CT prior to ECAP.