Issue link: https://iconnect007.uberflip.com/i/457216
36 The PCB Magazine • February 2015 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, evaluation of results, draft review, etc., are made during these calls, by those in attendance. The call minutes are documented 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, alu- minum wire bondable, and an excellent con- tacting surface, with a minimum shelf life of 12 months under standard storage conditions. The immersion gold layer protects the underly- ing 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 Specification was issued in 2002, and at the time of setting the specifi- cation 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 thickness shall be 0.05 [1.97 µin], at four sigma (standard de- viation) 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 specifi- cation had a statement for suggested typical val- ues 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 spec could be lifted, to limit the typical pad size to be measured and to make the specification applicable to LF solder and LF conditioning. This entails an extensive RR study, presently in progress. The intent is that the revised IPC-4552 Rev A would also include the following Additional Documents: • Test method (TM) for stripping immersion gold during failure analysis • Test method for determining the phos content of electroless nickel • A corrosion chart setting acceptability criteria for nickel corrosion (black pad) Immersion Silver (IAg) IPC 4553 A, 2009 IAg is a thin, immersion silver deposit over copper. It is a multifunctional coplanar surface finish, applicable to soldering. It may also be ap- plicable for some press-fit connections and as a contact surface. It has the potential to be suit- able for aluminum wire bonding. The immer- sion silver protects the underlying copper from oxidation over its intended shelf life. Exposure to moisture and air contaminants, such as sulfur IPC PLATING SUB-COMMITTEE 4-14: SURFACE FINISH SPECIFICATIONS continues feature