Effect of Boron on Microstructure and Properties of Sn-1.0Ag-0.5Cu Low-Silver Lead-Free Solder

Abstract

In this work, B (boron) was added into Sn-1.0Ag-0.5Cu (SAC105) solder alloy using mechanical alloying method in order to develop a new low-silver lead-free solder, Sn-1.0Ag-0.5Cu-xB, where B ranges from 0wt% to 0.2wt%. The melting characteristics, wettability, mechanical properties of welded joints, and microstructure of this solder were studied. The results showed that with adding B into SAC105 alloy, the melting point and melting range was not obviously changed. Although the wettability decreases with the B content increasing, the solder joints exhibited higher shear strength. As a result, the shear strength was the highest at the B content of 0.2wt%. For example, the shear strength of the Sn-1.0Ag-0.5Cu-0.2B solder was 35.12MPa, while that of the B free SAC105 solder was only 28.94MPa. Furthermore, adding B had a significant effect on grain refinement on the SAC105 solder . Observations on solder matrix and weld joints by SEM showed that the IMC thickness of solder joints with the addition of B was less than the SAC105 lead-free solder. Moreover, with the addition of B, the solder grains were refined obviously which had the effect of refining straitening, and the growing rate of brittle IMC in solder joint could be effectively reduced during soldering and aging process. Thus solder joint performance can be improved significantly.

Investigation of the Mechanical Properties of Mn-Alloyed Tin-Silver-Copper Solder Solidified with Different Cooling Rates

“…The strength of the bulk material appeared to be the weakest. The Mn precipitates caused grain refinement of β-tin grains inside the solder bulk as reported in the literature [ 20 , 21 ]. However, the finer grain structure did not necessarily yield a higher shear force.…”

“…Recently, materials such as manganese, boron, cerium and titanium have been added to the plain SAC alloys to improve their mechanical response for dynamic loads, such as drop-shocks or thermal shocks. Wang et al revealed that adding boron can reduce the rate of growth of interfacial intermetallic layers, which can slow down crack propagation over the lifetime of electronics [ 21 ]. Because of the reasonable price and harmless nature, manganese can be an optimal alloying element for the SAC solder alloys.…”