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The evolution of surface finish products have been on the fast track just to meet the complexity of newer designs (lighter, faster, smaller) as handheld devices like iPods, smart-phones, PDAs, digital cameras, camcorders, scanners, etc., continue down the form factor path. There has also been the need to meet the challenge of RoHS compliance and the need to have lead-free finishes and more importantly, lead-free compatible finishes.
Surface finish is about connectivity. It is the surface which forms the connection between the board and a device. Today, there is an impressive lineup of surface finish products. Among those finishes are ENIG and ENEPIG.
ENIG is still a growing surface finish, due to its versatility and wide range of applications: It is a planar surface finish; it is solderable through multiple reflow cycles, with tin-lead and lead-free solders; it has excellent shelf life; it is aluminum wire bondable; it is an excellent electric contacting surface; and the electroless nickel imparts strength to the plated through-hole. Today, there is a better understanding of the nickel corrosion issue and manufacturers are able to stay clear of the defect.
ENEPIG is back on the front burner after the issuance of IPC-4556 (ENEPIG specification). ENEPIG offers all the attributes of ENIG with the addition of gold wire bonding and the elimination of any probability of nickel corrosion. ENEPIG makes the most robust solder joint with lead-free, copper-bearing SAC type solders, and it has been the fastest growing finish for the last four years.
Editor's Note: This article, co-authored by George Milad and Don Walsh, originally appeared in the June 2013 issue of The PCB Magazine.
