Micross

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A New Surface Finish for the Electronics Industry
Keywords: silver, wirebond, solderability
In this presentation the authors will describe a new surface finish that achieves superior solderability, wire bondability, and corrosion resistance. By using chemically plated nickel –silver this finish provides these capabilities at lower cost than traditional finishes relying on much higher cost metals such as palladium and gold. In addition, the lower cost of silver permits a thicker coating providing a more robust performance compared to the very thin coating of chemically plated palladium and gold. A chemically plated finish is also desirable over electrolytic alternatives due to the capability of plating isolated features and enabling wider design options . One common surface finish now frequently used in the electronics industry is immersion silver. The popularity of this technology has increased over the last decade and now likely accounts for about 10-15% of final finish market. The popularity of immersion silver is driven by factors such as, excellent solderability, very low contact resistance; easy of assembly and testing, and it is a relatively low cost option. A widely used alternative to the above that is frequently used for high reliability applications, is electroless nickel-immersion gold (ENIG). This technology also is not without its problems. A common example, which can arise through the use of a poorly formulated process, is the well known phenomenon of “black line nickel”. This issue has been of significant concern to the electronics industry for some time and has damaged the reputation of ENIG as a final finish. The potential for black line nickel to occur has in some cases limited its wider adoption. With all of the above in mind and taking into account the very high price gold can achieve on the open market (which is currently in excess of $1400 per troy ounce) the industry is looking for an alternative final finish. Ideally, a suitable alternative would retain the positive features of the ENIG process whilst, at the same time, eliminate the black line nickel concern and, of course, be economical. This paper describes such a process, chemically plated nickel-silver. Careful choice of the electroless nickel, and silver processes results in a surface finish that has superior performance while remaining low cost. Process and performance capability will be given in the presentation including environmental resistance, wirebonding compatibility and solderability
John Ganjei, Advanced Technology Manager
MacDermid Inc.
Waterbury, CT
USA


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