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12 The PCB Design Magazine • April 2015 IPC SURFACE FINISH SPECS UPDATE continues feature before the final draft is issued. At this time the IPC takes on the task of publishing the docu- ment in its final format. The IPC Plating Sub-committee 4-14 has been active since 2001. It is co-chaired by my- self and Gerard O'Brien of ST and S Group. The IPC liaison is Tom Newton. The sub-committee has an exten- sive member list composed of OEMs, contract assemblers, board manufacturers, chemi- cal suppliers, as well as labs and consultants. The committee operates through one-hour, bi-weekly conference calls. Calls are held every other Wednesday at 11:00 a.m., EST, and every- one is welcome to participate. A notification e-mail is sent out before each conference call. All decisions pertaining to initiation and follow up on round-robin studies, evalua- tion of results, draft review, etc., are made during these calls, by those in attendance. The call minutes are document- ed and circulated. Since its inception, the IPC Plating Sub- committee 4-14 has issued the following: • IPC-4552 ENIG Specification 2002 • IPC-4553 Immersion Silver specification 2005 • IPC-4554 Immersion Tin Specification 2007 • IPC-4553A Revised Immersion Silver 2009 • IPC-4554 Amended Tin Specification 2011 • IPC-4552 Amended ENIG Specification 2012 • IPC-4556 ENEPIG Specification 2013 Following is a discussion of each of the above: Electroless Nickel/Immersion Gold (ENIG) IPC-4552, 2002 ENIG is a coplanar surface finish composed of a nickel layer capped with a thin layer of gold. The ENIG surface finish is solderable, aluminum wire bondable, and an excellent contacting sur- face, with a minimum shelf life of 12 months under standard storage conditions. The immer- sion gold layer protects the underlying nickel from oxidation/passivation over its intended shelf life. Thickness specifications are set to ensure the ability of the finish to meet the above criteria. The ENIG IPC-4552 Spec- ification was issued in 2002, and at the time of setting the specification for ENIG, no lead-free (LF) solder was in use. For thickness, IPC-4552 stated: • The EN thickness shall be 3–6 µm [118.1 to 236.2 µin] The IG minimum thick- ness shall be 0.05 [1.97 µin], at four sigma (standard devia- tion) below the mean; typical values for IG of 0.075 to 0.125 µm [2.955 to 4.925 µin] Although no upper limit was set, the specification had a statement for suggested typical values for IG of 0.075 to 0.125 µm [2.955 to 4.925 µin]. These values were erroneously interpreted to be the specification. The ENIG specification was amended in 2012: • The lower limit for thickness was reduced from 0.05 µm to 0.04 µm (1.6 µin) with the fol- lowing restrictions: – Limited time from manufacturing to assembly – Demonstrate the consistency of the plating process – Ability to measure low gold thickness Presently, the ENIG 4552 is in revision and should be out in 2015 (Revision A). The objec- tive of the revision is to set new lower and upper thickness limits for the immersion gold, to de- termine if the restrictions in the amended ENIG enIG is a coplanar surface finish composed of a nickel layer capped with a thin layer of gold. the enIG surface finish is solderable, aluminum wire bondable, and an excellent contacting surface, with a minimum shelf life of 12 months under standard storage conditions. " "