Electrodeposition And Solderability Of Sn-SiC Composite Coatings

Lead is a proven toxic substance which can cause a range of negativeimpacts on both the environment and the human. The application of Sn-Pb alloyhas been restricted or prohibited in microelectronics and other industrial fields.So it is imperative to develop lead-free solderable coatings. In the study, weused composite electrodeposition technology to get Sn-SiC composite coatings.It is aimed at developing composite coatings with low cost and high reliability torealize industrial production and promote lead-free process in electronicelectroplating.In this study, firstly we confirmed the compositions of the basic bath byorthogonal experiment as follows:55g/L Sn(CH3SO3)2,160g/L methyl sulfonicacid (MSA) and10mL/L OP-emulsifier. Adding SiC particles to the basic bath,we studied the effects of bath compositions and electroplating process conditionson the performance of composite coatings. The incorporation of SiC particles incoatings could refine the crystalline grains; the performance of coatingsincorporated with nano-sized SiC was better than that of coatings incorporatedwith micron-sized SiC. Increasing bath temperature made the Sn matrix finelycrystalline, and the quality percentage of SiC was above2wt.%for each coatingin this group. Current density too high or too low can refine Sn crystalline grains,but was not good for the incorporation of SiC particles. Sn-SiC compositecoatings electrodeposited in a bath containing30g/L SiC particulates and50mg/L sodium dodecyl sulfate (SDS), at an inclination angle of the plating tank θof45°, a temperature of20℃and a cathode-current density of3A/dm~2in DCplating had a large solder spreading area and a good tin whisker resistance. Inpulse plating with average current density of1.75A/dm~2, coatings deposited atfrequency of50Hz had better solder spreading performance, and coatingsobtained at frequency of100Hz, duty cycle of20%~50%had highest SiCcontent and better tin whisker growth resistance.The variations of coating’s solder spreading performance and tin whiskerresistance with contents of SiC in coatings were studied. Composite coatingswith quality percentage of SiC between0.3wt.%and2.3wt.%had better solderspreading performance than pure Sn coating. In DC plating, when content of SiCin coatings was between1.0wt.%and2.3wt.%, coatings had smaller Sn whiskerthan that of pure Sn coating. In pulse electroplating, when content of SiC in coatings was above3wt.%, coatings had better tin whisker resistance. The XRDanalysis results showed that composite coatings with SiC nano-particles had apreferred orientation, which was adverse to tin whisker growth. So the capabilityto inhibit tin whisker growth of Sn-SiC composite coatings was better than thatof pure Sn coating.