Transition of Bi embrittlement of SnBi/Cu joint couples with reflow temperature

The current study revealed the effects of reflow temperature and the reflow time on the interfacial embrittlement of SnBi/Cu joints. When the reflow temperature is below 220 degrees C, the joints reflowed for 150 min often fail in brittle mode because the Bi atoms from the SnBi solder easily segregated at the Cu(3)Sn/Cu interface. In contrast, Bi embrittlement did not occur for joints reflowed at above 260 degrees C for 150 min because the Bi particles were frozen in the Cu(3)Sn layer during the formation of intermetallic compounds (IMC) at the initial reflow stage, mainly located at the Cu(3)Sn grain boundary. It is interesting to note that the Bi embrittlement did occur when the joints were reflowed at above 260 degrees C for 250 min, which should be attributed to Bi diffusion. It is concluded that the Bi particles are frozen in the Cu(3)Sn layer with increasing reflow temperature, that cannot eliminate Bi embrittlement, and can only delay the occurrence of Bi embrittlement.