Study And Preparation Of No-clean New Flux For Lead-free Solder

This paper focused on the development direction of flux in the modern electronic assemblies. A flux formulation design principle was formed by exploring the mechanism of action of each component. Two products of no-clean water-based flux and no-clean flux including a curable film were prepared. And the properties were tested for these fluxes. The conclusions and results were obtained as follows:(1) A kind of no-clean water-based flux for lead-free Sn-0.7Cu solder was prepared. Microcapsules and compounding technology were used to achieve the balance between activities and corrosives, and the main components of the flux were optimized. In the formula, the active agent was a complex composition of succinic acid, adipic acid, and triethanolamine. The dosage of active agent, auxiliary solvent, surfactants, and film forming emulsifiers were2.2%,15.0%,0.1%and0.5%respectively. The properties were tested for this flux, and the results suggested that the flux was halogen free, non-corrosive of residue, appropriate pH and surface insulation resistance (pH approaches6.0and SIR accesses to2.1×1011Ω), low solid(less than5.0%) and low ion contamination. The diversified properties of the no-clean flux met the standard requirements, and it achieved an excellent soldering performance and an average expansion rate of78.0%. For the preparation of the flux, the deionized water was served as the solvent, and it was environmental protection because of the reduced content of VOC.(2) This article put forward an innovative design idea of no-clean flux including a curable film with respect to the problems of no-clean flux’s reliability. The cured epoxy resin exhibits an excellent stability of mechanics and electric, and was chosen to film forming emulsifiers of flux. On the basis of curing system, the active agent, solvent and surfactants in fluxes were selected respectively. In this formula, the active agent was compounded with2:1weight ratio of citric acid and succinic acid, an epoxy resin A was choose as the film-forming agent, an acid anhydride B was selected as curing agent, the solvent was a complex composition of anhydrous ethanol and glycerol. The dosage of active agent, film forming emulsifiers, curing agent, and solvent were3.9%,9.3%,6.5%,79.7%respectively. The composition was optimized, and the properties were tested for the flux. The results suggested that the flux is halogen free, and it achieved an excellent soldering performance and an average expansion rate of80.0%. The surface insulation resistance reached to1.1×1012Ω. and electrochemical migration was not obvious. After soldering, the curing film performed an excellent mechanical property with the impact strength reached17.5kJ/m2, and the reliability of solder joint was improved effectively.