| Sn-3.0Ag-0.5Cu(SAC305)/Cu solder joints with different reflow times were prepared by reflow oven,The solder joints were tested by aging treatment at 48th,96h,144h,192h,and 240h respectively at the temperature of 150℃.The modification of SAC305 solder was studied,and the reliability of Sn-0.3Ag-0.7Cu-0.5Bi-Ni(SACBN)and Sn-3.0Ag-3.0Bi-3.0In(SABI)solder was studied,the following conclusions are obtained:1.The relationship between the interface layer thickness of Sn-3.0Ag-0.5Cu solder joints and the aging treatment time is:One time reflow:dt-3.1119 =0.2230t1/2,the growth coefficient is 0.0497 μm/h1/2.Two times reflow:dt-0.8241 = 0.5119t1/2,the growth coefficient is 0.2620 μm/h1/2.Three times reflow:dt-1.6925 = 0.5625t1/2,the growth coefficient is 0.3164 μm/h1/2.Four times reflow:dt-4.1414 = 0.8137t1/2,the growth coefficient is 0.6621 μm/h1/2.With the increase of reflow times,the growth coefficient becomes larger.The relationship between growth coefficient(y)and reflow times(x)is that:y =-0.1504 + 0.1892x,there is a linear relationship between them.2.The expansion rate of Sn-3.0Ag-0.5Cu is 76.75%and the wetting angle is 22.11°.The expansion rate of SACBN solder is 74.15%and the wetting angle is 25.87°.The exqpansion rate of SABI solder is 87.38%and the wetting angle is 8.89°.The wettability of SACBN and SAC305 solder is similar to that of Sn-37Pb solder.The wettability of SABI is better than that of SAC305 and Sn-37Pb solder.3.The relationship between the thickness of the interface layer of SACBN and SABI and aging time is:SACBN:dt-0.4374 = 0.1813t1/2,the growth coefficient is0.0329.SABI:dt-2.5735 = 0.0611t1/2,the growth coefficient is 0.0037.The thickness of intermetallic compounds layer of SAC305 were the largest at different aging time.The thickness of intermetallic layer of SABI is greater than SACBN in the early stage of aging,with the extension of aging time,the IMC thickness of the SABI was close to SACBN and then less than SACBN.This is because the growth coefficient of intermetallic compounds of SABI is far less than SACBN.4.Based on the study of diffusion dynamics,it is found that the Ag3Sn and the Bi at the crystal boundary can inhibit the growth of intermetallic compounds,the addition of Bi and Ni can inhibit the formation of cracks.The addition of Ni element can get tiny and dispersed distribution of intermetallic compounds,the thickness of IMC layer of SACBN is thinner than that of SAC305,and the growth coefficient is lower,moreover,the cost is saved.Meanwhile,it shows better reliability at the long time aging.The addition of In can improve the wettability of solder.The thickness of IMC layer of SABI is greatly reduced than that of SAC305,and the growth coefficient is greatly reduced than that of SAC305,wettability is greatly improved,SABI shows better reliability at long aging time. |
