Issue link: https://iconnect007.uberflip.com/i/1411055
SEPTEMBER 2021 I PCB007 MAGAZINE 77 2007. For immersion tin, the committee spec- ified a lower limit for thickness. e relatively thick value of 1 micron was chosen to ensure that enough virgin tin would be available at the surface for soldering aer storage. It is well un- derstood that tin forms an intermetallic (IMC) layer with the underlying copper, and that this layer continues to grow in thickness over time. e immersion tin thickness will be: 1.0 µm (40 µ") minimum at -4σ from process mean as measured on a pad of area 2.25² µm (3600² mils). Typical value of 1.15 µm (46 µ") to 1.3 µm (52 µ"). e Immersion Tin Specification IPC-4554 was amended in 2011. e amendment ad- dressed solderability testing and specified the allowed stress testing conditions for the depos- it and the type of fluxes to be used for both tin- lead and LF (lead-free) testing. Specification IPC-4555 for OSP (organic sol- derabilty preservative) was attempted in 2008. Aer more than one year of struggling with Specification IPC-4555, nothing was specified. ere was no consensus arrived at. is was mostly due to the wide assortment of organic products that were used for solderability pres- ervation for the various applications, each with its own recommended thickness values. In 2009, the Immersion Silver Specifica- tion IPC-4553 was revised and Immersion Sil- ver IPC-4553A was issued in 2009. e origi- nal specification with a thin and a thick speci- fication was confusing and hard to understand. In addition, the industry settled on one type of immersion silver, and it necessitated the issu- ance of a single thickness specification, with the addition of an upper spec limit: IPC-4553A specified a single thickness with an upper limit: • 0.12 µm [5 µin] minimum to 0.4 µm [16 μin] maximum at ± 4σ from process mean as measured on a pad area approxi- mately 2.25 mm², example; 1.5 mm X 1.5 mm (60 X 60 mil). Typical value between 0.2 µm [8 µin] to 0.3 µm [12 µin]. • An upper limit was set. In 2012, IPC-4552 ENIG specification was amended to reduce the lower limit of immer- sion gold thickness. e lower limit for gold thickness was reduced from 0.05 µm to 0.04 µm (1.6 µin) with restrictions: • Limited time from manufacturing to assembly • Demonstrate the consistency of the plating process • Ability to measure low gold thickness IPC-4556 ENEPIG, 2013 e document produced is very compre- hensive and includes a wealth of information from the RR studies that were conducted. e appendix contains a documentation of these studies, each authored by the person who con- ducted the testing. It also includes a section on the proper methods of equipment setup for a reliable measurement of very thin layers of metal deposits. Appendices 1–9 1. Chemical Definitions and Process Sequence; Martin Bayes, Dow Chemical Company 2. Round Robin Test Summary; George Milad, Uyemura International Corporation 3. ENEPIG PWB Surface Finish XRF Round Robin Testing; Gerard O'Brien, S T and S Group. 4. Factors Affecting Measurement Accuracy of ENEPIG Coatings by XRF; Frank Ferrandino, Calmetrics Inc. 5. ENEPIG PWB Surface Finish Wetting Balance Testing; Gerard O'Brien, S T and S Group. 6. Solder Spread Testing; Brian Madsen, Continental 7. ENEPIG PWB Surface Finish Shear Test Project; Dave Hillman et al., Rockwell Collins Inc. 8. Gold Wire Bonding; Stephen Meeks, St Jude Medical 9. XRF ickness Measurements of thin