Comparative Study On SnAgCuBiNi And SAC305Lead-free Solder

Sn-3.0Ag-0.5Cu （SAC305） lead-free solder has been widely used in the electronicpackaging industry. However, the large lamellar-like Ag3Sn will form during the soldersolidification, the slower cooling speed, the more serious coarsening of Ag3Sn. CoarseningAg3Sn will reduce the reliability of solder joints and high Ag content will also increase thecost of the solder alloy. Based on this, the low Ag Sn-0.8Ag-0.5Cu-2.0Bi-0.05Ni （SACBN）lead-free solder has been developed.Firstly, the effects of three different cooling rates （furnace-cooled, air-cooled andwater-cooled） on microstructure and mechanical property of SACBN and SAC305solderhave been comparatively studied.The results show that as the cooling rate increases, theprimary β-Sn grain size decreases in the two kinds of solder alloys, and proportion of primaryβ-Sn phase increases and eutectic phase decreases. The faster the cooling rates, the higher themicrohardness. Moreover, microhardness of SACBN lead-free solder alloy is higher thanSAC305solder.Secondly, the interface reaction between liquid SACBN, SAC305lead-free solder andCu substrate at240,250,270,300℃has been comparatively investigated. The results showthat (Cu_1-x,Ni_x)₆Sn₅and Cu₆Sn₅phase are formed at the SACBN/Cu and SAC305/Cu solderjoints during soldering, respectively, and Cu3Sn is observed between (Cu_1-x,Ni_x)₆Sn₅, Cu₆Sn₅phase and Cu substrate with the soldering time and temperature increasing. The average IMCgrain size of SACBN/Cu and SAC305/Cu interface follows linear relationship with the cuberoot of soldering time at250℃. Moreover, the IMC grain size of SACBN/Cu interface issmaller than SAC305/Cu. Both kinds of solder interfacial IMC thickens constantly withsoldering time and temperature increasing. The higher the soldering temperature, thefaster the IMC layer grows. The thickness of SACBN/Cu interface is thinner than SAC305/Cuinterface during the soldering process, but there is more consumption of Cu substrate forSACBN lead-free solder.Finally, the interface reaction between solid SACBN, SAC305lead-free solder and Cu,electroless Ni plating substrates has been comparatively studied. The results show that the interfacial IMC thickens constantly with aging time increasing and the higher the agingtemperature, the faster the IMC layer grows. The growth of interface IMC is controlled bydiffusion mechanism. The IMC growth activation energy of SACBN/Cu, SAC305/Cu,SACBN/Ni-P, SAC305/Ni-P are111.70,82.35,58.36,65.18kJ/mol, respectively. In general,the shear strength of aged solder joints declines continuously during aging process. However,SACBN solder joints exhibit better shear strength than SAC305solder joints.