Research And Development Of A Soldering Flux For Lead-free Solder Wires In Al Soldering Process Of Electronic Packaging

The aluminum soldering technology in electronic packaging has attracted more and moreattention recently, because aluminum and its alloys show many advantages in application,such as low density, good thermal and electrical conductivity, good corrosion-resistant as wellas low cost. However, due to the existence of a dense and stable layer of oxide film, thesoldering process performance of aluminum and its alloys is very poor. More importantly,when soldering Al and its alloys by low-coat lead-free solders, the soldered joints are prone toelectrochemical corrosion, thus significantly affecting the mechanical reliability of the joints.Furthermore, there is an acute need for the lead-free solder wire used flux with goodperformance in curing and storage stability. Clearly, the above three technical problems havehindered the widespread application of aluminum soldering technology using flux-coreslead-free solder wires.This thesis study aims to explore the flux composition design for flux-cored lead-freesolder wires to be used in aluminum soldering technology. The wetting test, corrosion tests,spreading test, curing test were performed to obtain the optimal selection of basic constitutesof active ingredients, carrier and surfactant. After conducting a systematical study on thephysical state of the active agent system, concentrated time, soldering properties of carriers,influence of covering additive on the electrochemical corrosion behavior, effect of surfactanton properties of spreading, then the optimal composition design of the flux and the integratedprocessing route have been achieved. Furthermore, a comparative study between oursoldering flux and other two commercial soldering fluxes available in the market has beendone to further optimize the composition design of the flux. Finally, the flux-cored lead-freesolder wire for soldering aluminum and its alloys was successfully manufactured. The mainconclusions drawn from this thesis study are as follows:(1) It has been shown that after neutralizing ammonium and multi-amine and hydroxylproportionally, the flux system exhibits the reduced corrosion to the solder joints, whilewettability having been improved significantly. (2) The results show that the combined fluorine-containing ammonium and multi-amineand hydroxyl groups can well cured, and the subsequent flux has relatively strong activitywithout water-soluble carrier, this has been proved to be a good solution to solve the problemin wire-drawing process.(3) It has also been shown that the concentration process can increase the solder abilityof the flux. The specific fluorine-containing ammonium A and organic amine C can be bestconcentrated at a time period of40min; the fluorine-containing ammonium B and organicamine C can be best concentrated after80min.(4) It has been founded that Zn salt content has a significant impact on theelectrochemical corrosion resistance of solder joints, and the influential role of Zn salt and itsoptimal content have been determined.(5) After making Sn-Cu soldering wires by our flux, the over all comparison inprocessing performance between our soldering flux and other two commercial solderingfluxes shows that the flux developed by this thesis study has superior processing propertiesover one commercial flux, while being as good as the other one.