Research On Low Silver SnAgCu Lead-free Solder Paste

Solder paste is the key material for surface mount electronics technology (SMT) inelectronic products. In recent years, due to its relatively high cost-efficiency, low silverSnAgCu (SAC) lead-free solder has become popular in the electronic industry. In thispaper, spread experiments, combined with thermal analysis methods was used to selectcomponents of the flux and determine their contents by orthogonal experiment methods.And then the performances of the prepared flux were tested according to the relevantstandards. At last, mixing the optimized flux with SAC0307low silver lead-free solderpowder in a certain proportion, prepared low silver lead-free solder paste, and itsperformances were tested in comparison with commercial solder paste. Main conclusionsof the study are as follows:(1) The solvent is the complex solution of alcohol B: ether C: alcohol in mass ratio of5:3:2; When the mass ratio of hydrogenated rosin and polymerized rosin is1:2, the slumpresistance of solder paste and the residual after soldering can be balanced; Whencompounds of adipic acid: succinic acid: acid F in mass ratio of7:1:2is selected as theactivator, the activity of the flux increased significantly; When the mass ratio oftriethanolamine and the organic acid is2:5, the pH and the activity of the flux can bebalanced; Meanwhile, when the activator has a superior solubility, a suitable melting point,boiling point, moderate acidity and good chemical stability, the solder can spread well.(2) The order of factors influenced on solder spreading rate is: activator> Rosin>surfactant. The composition of flux including (mass fraction):35%rosin,7%activator,1%surfactant,5%thixotropic agents,3%film former,0.1%corrosion inhibitor,0.1%anti-oxidant,1%stabilizer, and solvent. The prepared flux is a stable, homogeneous andbrown viscous paste, which have pH5.07, non-volatile content of67.87%, halide-free, lowcorrosion, good drying properties, good wetting properties and no stratification orcrystallization during storage.(3) When3#SAC0307low silver lead-free solder powder and flux are mixed in massratio of88:12, the prepared solder paste is even delicate with a moderate viscosity.(4) Compared with commercial solder paste, the solder ball test results of both solderpastes are1level, and both of the solder spots are in-erratic. The thermal collapse rate ofthe prepared solder paste and the commercial solder paste are0.17mm and0.11mm,respectively. Both of them have good anti-thermal collapse performance; The spreading area of the prepared solder paste and the commercial solder paste are58.33mm2and59.01mm2, respectively. The both wetting performance test results are2level; There arerarely residue and no corrosion of the both after soldering. There is no obvious defects insolder spots of the prepared solder paste, while a small amount of pores in commercialsolder paste; So, the former has better soldering quality.