Application Of New Palladium Salt In Electroless Plating Process

Copper baseline circuit and pad of printed circuit board?PCB?are easy to oxidize,which results in circuit resistance increasing and affects product reliability.At present,copper lines are protected by surface treatment,and the protection layer needs to meet the installation requirements of different processes and components.With the integration and miniaturization of electronic devices,there are more and more requirements in functionality for the coating.The traditional surface treatment technology cannot meet the demand.The demands for"universal coating"electroless nickel/electroless palladium/immersion gold?ENEPIG?process and lower cost electroless nickel/electroless palladium?ENEP?process are increasing.Electroless nickel/immersion gold?ENIG?process is relatively mature,and the relatively backward electroless palladium technology restricts the marketization process of ENEPIG process,so it is very important to study the electroless palladium plating process.In this paper,electroless palladium plating bath was developed by using palladium tetraammonium sulfate as main salt,ethylenediamine,disodium ethylene diamine tetraacetic acid disodium salt?EDTA-2Na?and sodium citrate as complexing agent,sodium hypophosphite as reducing agent,4-dimethylaminopyridine as stabilizing agent,sodium dihydrogen phosphate and disodium hydrogen phosphate as p H stabilizing agent.The effects of complexing agent and reducing agent on the deposition rate and stability of electroless plating bath,the morphology and element composition of electroless plating bath were studied by X-ray,electron microscope,energy dispersive spectrometer and constant temperature test.By designing and optimizing the orthogonal experiment,the plating bath formula was obtained as follows:Pd?NH₃?₄SO₄ 1g·L^-1,ethylenediamine 4g·L^-1,EDTA-2Na 4g·L^-1,sodium citrate 10g·L^-1,sodium hypophosphite 8g·L^-1,4-dimethylaminopyridine 1ppm,sodium dihydrogen phosphate0.6g·L^-1,disodium hydrogen phosphate 0.2g·L^-1.Then by single factor expriments were designed to acquire optimum conditions were T=51?57?and p H=7.0?7.6.The optimized electroless plating bath has high stability and fast deposition rate.At the same time,this paper uses a new type of palladium salt to replace the activation steps in the pretreatment of printed circuit boards.By comparing with the traditional palladium sulfate activation system,a new type of activation solution is obtained.Finally,the developed plating solution was applied to ENEPIG and ENEP processes,and the obtained composite coating had compact and smooth surface,along with strong adhesion and high corrosion resistance.The solderability and reliability of the coating were verified by tin dipping test and gold wire drawing test.