Study On Electroless Ni-P Film Plating In Microelectronic Packaging

With the development of technology,the electronic products are tending to miniaturization,and the microstructure and morphology of soldering points are remarkably changed.Packing density is obviously increased as well.So the microelectronic packing has become one of the most important and challenging technology in the electronic industry nowadays.As a joining material,solders play an important role in microelectronic packing. And interfacial reaction between the solder alloys and the UBM is a critical point for the effect on the reliability.Electroless Ni-P has been widely used in the microelectronic packing in the recent years because of the better solderability and diffusion barrier.The technical investigation on electroless Ni-P on Al substrate was studied in the present work.The objective was to optimize the pretreatment process and gain a Ni-P plating with better properties which is applied to electronic packing,and to find out the controllability of technological parameters by optimizing the plating process.Also the examination and evaluation of reliability were concluded.After gaining the.electroless Ni-P plating with better properties,the interfacial reaction of Sn-3.5Ag/Ni-P was investigated after soldering and aging in order to explore the growth mechanics of IMC and the change of Ni-P component.The major conclusions are as follows:1.Comparative study on conventional high,medium,low concentration of zincating solution was carried out during the pretreatment on AI substrate.And a good zincating solution with the compositions of 120g/L NaOH,20g/L ZnO,20g/L C₄H₄KNaO₆·4H₂O,2g/L FeCl₃,1g/L NaNO₃ was gained.On the investigation on 1^st zincating,a better zincating process of 10% HNO₃ and operating time of 5～6s was found by comparing the corrosion and the zincating effect during zincating in different concentration of HNO₃ and HCl solution.On the investigation on 2^nd zincating,a zincating time of 30s was good.After 2nd zincating for 30s, the surface of Al substrate was fully covered by Zn particles and it was a monolayer of Zn.2.In the present work,the mutual effect of concentration of NiSO₄,reductant,complexing agent and pH value on the deposition rate and P content was investigated by the orthogonal test. The results shows that the effect of pH value on the deposition rate and P content is pronounced, and the effect of concentration of NiSO₄ and reductant is less pronounced,while the effect of concentration of complexing agent is minor.In the acid solution with the pH value in the range of 3.5 to 6.0,the P content is decreased as the pH value increased from 22.5 at.%(pH=3.5) to 12.6 at.%(pH=6.0).However,the deposition rate is increased with the increasing pH value before the deposition rate reaches the maximum value of 21.0um/h(pH=5.0).The deposition rate remains unchanged when the pH value exceeds 5.0.And the P content is decreased from 17.2at.%to 12at.%with the increasing concentration of NiSO₄ from 18g/L to 28g/L,the deposition rate is increased from 16.um/h to 21um/h as well.When the concentration of NaH₂PO₂ increased from 18g/L to 28g/L,the P content was increased from 12.9at.%to 15.6at.%and the deposition rate was increased from 18um/h to 23um/h.At the concentration of 26g/L NaH₂PO₂,the deposition rate reached the maximum.The gained plating solution has good stability,and after plating,the amorphous Ni-P plating has good adhesion on Al substrate.3.The interfacial reaction of Sn-3.5Ag/Ni-P(Ni-6.5wt.%P,Ni-8.5wt.%P) was investigated during the soldering and aging.The wetting angles and spreading coefficients showed that there was no effect of P content on the wettability though some minor changes were found during soldering at 250℃.The phases of interface from solder to substrate were Ni₃Sn₄, Ni-Sn-P,Ni3P and Ni-P respectively.After aging,rod-like morphology of IMC was appeared. And there was no effect of P content on the microstructure of Sn-3.5Ag/Ni-P interface during soldering for different time,except that Ni-P was absolutely consumed in the case of Ni-8.5wt.%P after 30min soldering.During the aging of 5min solder point,the thickness of IMC increased with aging time increasing.Meanwhile,the thickness of Ni-Sn-P and Ni₃P was thickened with aging time.For Ni-8.5wt.%P,the initial Ni-P plating was absolutely consumed after 200h of aging.