Direct immersion gold (DIG) as a final finish

Abstract

PurposeTo report on research on the alternative surface finish “direct gold on copper”, including reaction mechanism, methods of deposition and end uses.Design/methodology/approachExamines the deposition reaction of the electroless flash gold plating bath, and the effects of the copper surface roughness and deposition time on the deposit and solderability characteristics.FindingsDirect immersion gold is only partially immersion and mostly electroless in deposition mode. The surface is applicable to soldering for both leaded solder and lead‐free solders. The surface is also wire bondable.Originality/valueThe paper offers details of a new alternative surface finish for use in printed circuit board fabrication as well as in packaging applications. The paper shows the electroless deposition mode of the process. The finish is ideally suited where Rf losses must be minimized. It is suitable for soldering as well as for wire bonding.

Solder joint reliability with various silver finish on PCB

“…The cost of Au, however, is high. At the same time, Ni layer that has high resistance is necessary between Au and Cu base to prevent Cu diffusion to Au surface because another solution thick Au is too expensive to be adopted [5]. Such issue can be solved by low cost Ag finish, which also has silver color preferred in LED packaging.…”

“…Although immerging Ag, widely used in mother board for good soldering ability [3], is unqualified for wire bonding because of Cu diffusion through thin Ag to the surface [6]. It is the same issue as direct immerging Au on Cu [5], but electroplated thick Ag can solve the problem without exorbitant price and has been widely used in lead frame package for wire bonding [2,7]. The solder joint performance of electroplated Ag, however, has not been evaluated in prior studies.…”