Research On Chemical Immersion Palladium On Print Circuit Board

A diffusion barrier of palladium metal between the nickel layer and a gold layer of the PCB surface is introduced by immersion palladium method in the ENIPIG(electroless nickel/immersion palladium/immersion gold)process.The characteristic of the process is using the method of immersion palladium to replace the traditional eletroless palladium.The procedure of immersion palladium maintains the advantage of eletroless palladium:prevent producing metal compound in nickel layer and gold layer interface and eliminate the“black plate”phenomenon fundamentally.What's more,it is easier to control the thickness of Pd,reduce production costs and better dense,stronger tensile properties.The procedure of ENIPIG is that:firstly electroless Ni;Then using the immersion method depositing palladium,the depositing thickness of palladium is 0.03?m-0.05?m in 2 min;lastly immersion gold.The optimized palladium formulation:0.8g/L Pd,48-56m L/L(m/m 27%)NH_3?H₂O,6g/L Citric Acid,60-100g/L composited modifier A,0.05m L/L brightening agent B.Under the condition of p H=5.0±0.2,t _Pd=2min,T=40?,the immersion palladium solution had low Pd ion concentration,easily control p H,long bath life for 5MTO and good stability.(1)It discussed the increase of the palladium ion concentration to the thickness of Pd.It suggested that when the Pd ion concentration was less than 0.8g/L,the thickness of the Pd increased with the increasing of the Pd ion.when the Pd ion concentration greater than 0.8g/L,the deposition thickness of the palladium stabilized.(2)It discussed the increase of the ammonia concentration to the thickness of Pd.The deposited thickness of the palladium layer is too thin with low ammonia concentration.When the ammonia concentration is too high,the deposited thickness of the palladium is also thin.(3)Additive composited modifier A,citric acid can stabilize the p H and the deposition rate of Pd.Under the conditions of 60-100g/L composited modifier A,6g/L citric acid,it not only can ensure rapid palladium,uniform coating but also keep the resulting palladium solution stable.(4)It discussed the effect of p H,plating time,temperature to the rate of Pd.When the p H=4-6,the rate of the Pd was stable;The rate of the Pd was decreased with the increasing of the time.In the first 2min,the rate was fast;The appropriate temperature is important,the layer thickness was nonuniform with high temperature,the layer was thin with low temperature.2.In response to these palladium layer of SEM,EDS,goldsmith lines and solder reflow had been tested.The results of SEM suggested that immersion palladium layer surface uniform and dense without cracks;The results of EDS suggested that the Pd layer could fundamentally prevent PCB"black plate".The introduction of Pd could increase the ability of goldsmith;The results of solder reflow suggested that the weldability is good.It is tested the stability constants of Pd with Citric Acid by UV spectrophotometry K=3.186×10⁵.It was discussed complexing agents NH₃,Cl^-,Citric Acid with Pd(?)complexes form by simulation software PHREEQC,theoretically accurately reflect the trends of C_Pd2+with p H and concentration of Citric Acid.The main form of Pd(?)is[Pd(NH₃)₄]²⁺in the solution.