Development And Improvement Of Halogen-free Soldering Flux For Lead-free Cored Solder Wires

The flux needs better reactivity,thermal stability and wetability due to the application of leadfree cored solder wire.And the requirement of no halogen and VOC places strict restrictions on the design of new flux.The rosin based flux has to meet both the environmental requirements and good activity to help soldering.This paper focused on Sn0.7Cu solder wire and studied the difference of using various components and the effects of mixing them together.The conclusions were drawn as following:(1)Spreading rate was used to analyze the activity of monobasic acids,dicarboxylic acids,triple carboxylic acids and hydroxycarboxylic acids.Dicarboxylic acids showed better activity than other organic acids under same conditions.Triple carboxylic acids and hydroxycarboxylic acids didn't function very well.It indicated that the activity would not necessarily be better when the acid value was higher.3% adipic acid and 6% suberic acid were used as activator considering the compatibility and the copper corrosion;(2)Water-white rosin showed great activity and esterified rosin G showed excellent thermal stability.Using water-white rosin and esterified rosin G as carrier can combine the solderbility and thermal stability together.The carrier occupied 85% of the flux.The solvent was composed of tetrahydrofurfuryl alcohol with good solubility and DBE which is environmentally benign and the ratio value at 4:1.Spreading rate was improved to 75.6% after adding 0.1% FSN-100;(3)Esterified rosin G generated few smoke during soldering and common rosin produced the most smoke particles.The fume formation rate increased as temperature rised.The smoke during soldering decreased obviously when esterified rosin G accounted for at least 30% of the carrier;(4)The spattering rate could be effectively reduced from 0.67% to 0.32% after using defoamer A which contains mainly polyacrylate.And the relationship between spattering rate and the vapor pressure of flux in enclosed space was studied.The result showed that the higher vapor pressure is the more serious spattering would be.