SURFACE FINISHES: METALLIC COATINGS OVER NICKEL OVER COPPER
Author: George Milad Company: Atotech USA Inc Date Published: 9/10/1996
Surface Mount International
Abstract: Fine pitch WIT devices are forcing the industry to look for alternatives to the traditional Hot Air Solder Leveling (HASL) process. Although HASL gives an excellent surface for solderability, it has its shortcomings. HASL finishes are not flat, they contain lead, are not aluminum or gold wire-bondable and the resulting board has already undergone a thermal excursion which can only have adverse effects on product effective life performance. Fine pitch work requires a flat coplanar surface for the precise application of solder paste in reflow and for ball grid array (13GA) assembly. Ultrafine pitch devices may require a wire bondable as well as a solderable surface. Both nickel/gold and nickel/palladium are surface finishes that can meet the demands of the evolving technology trends of today.