Study On The Lead-Free Solder Paste Prepared By Mechanical Alloying In SMT

Mechanical alloying (MA) technology is a new process to prepare solderpowders. There are particular advantages in controlling the composition of solderalloy, the distribution of impurities, the refining and dispersion of the second phase.In addition, MA process is a new exploration in the preparation of solder powders. Itis very important to investigate theoretically the reciprocity of alloy elements,theformation of new-phase and the interaction between alloy powder and milling media. The primary MA parameters in the preparation of lead-free solder powders wereobtained based on a number of experiments. Morphology of Sn-0.7Cu and Sn-3.5Agpowders, the course of mechanical alloying and the effect of ball milling conditionson the formation of mechanical alloy were analyzed using a scanning electronmicroscope (SEM), a differential thermal analyzer (DTA) and an X-raydiffractometer (XRD). The reactive mechanism of mechanical alloying Sn-0.7Cuand Sn-3.5Ag was educed. The microstructure and regular mechanical property oflead-free solder paste made from MA powders and RMA flux was investigated,compared with the ones made from cast. The results show that the lead-free solder powders and the size of particles canbe controlled under the proper MA parameters. As a surfactant, acetone appears to beeffective to accelerate the MA process. Ball milling parameters effects the formationof MA alloy significantly. The course of mechanical alloying Sn-Cu and Sn-Ag isdescribed as bonding and rupturing time and again, ensuing from which sheetmicrostructure was formed. The reactive mechanism of mechanical alloyingSn-0.7Cu and Sn-3.5Ag is that the mechanical-induced atom diffusion drivessubstitution solid solution and interface dissolution, as a result of which Cu6Sn5 andAg3Sn was formed. There is no distinct difference in spreading area and wetting angle between MApaste and cast solder, but the shear strength of the former is less than the one of thelater. The microstructure of Sn-0.7Cu (MA) is composed of Sn-rich phase, Cu6Sn5and Cu3Sn phase IMCs. The microstructure of Sn-3.5Ag (MA) is made up of Cu6Sn5 - II -ABSTRACTphase that was formed by copper atoms diffusion from copper board, Sn-rich phaseand Ag3Sn that evenly distributed in base body.