Issue link: https://iconnect007.uberflip.com/i/1527952
for their specific assembly process, poten- tially improving wire bonding performance or allowing for the use of a specialty contact resistance component. What we know is that thicker gold correlates directly to lower gold porosity. Lower gold porosity provides greater protection against nickel oxidation and bet- ter performance in harsh environments. ose two performance features are critical for sol- derless connections. What is the cost/benefit argument for moving to either of these processes? RAIG is a must for the consistent produc- tion of high-reliability ENEPIG PWBs. Using RAIG rather than conventional immersion golds will, however, slightly increase the cost of the immersion gold part of the ENIG or ENEPIG process. e main reasons are: • A typically higher gold content (grams/ liter) in the bath at operating conditions • e useful life of the bath may be restricted if not run frequently • e electrolyte can plate-out to the tank walls and plumbing more easily ere are, however, considerations relative to RAIG that close the cost gap: • RAIG for equivalent thickness typically has greater thickness control, which reduces gold usage • e high consistency of gold plating times when using ENEPIG improves efficiency, process reliability and yield, and lowers rework • RAIG completely eliminates nickel corro- sion on ENIG and ENEPIG work DIG is less expensive than ENIG and much less expensive than ENEPIG as a final fin- ish. DIG is a more expensive final finish than immersion silver. DIG is a specialty final finish and not con- sidered a premium final finish because, with- out the nickel, it has reduced solderability shelf life, but has shown some resistance to multi- less assembly, such as hydrostatic component connections. e second instance where RAIG offers a unique and clear advantage is for customers that specify highly reliable ENIG with zero nickel corrosion. Even the highest reliability immersion golds cannot guarantee zero nickel corrosion. OEMs do specify "zero EN cor- rosion." For many PWB manufacturers, the desire to exceed IPC-4552 Rev B stems from the fact that, in the event of a part failure in the field, the presence of any nickel corrosion will be central to what follows. Even absent defin- itive causation, this correlation will open the PWB manufacturer to potentially crushing lia- bility. is risk is sufficient for many manufac- turers to implement what is considered the best available finish gold technology. Figure 5 shows an ENIG-RAIG micro-sec- tion analysis aer the part was exposed to dou- ble the normal process dwell time. is is an example of a corrosion analysis of an ENIG part, with a 40-minute dwell time in an RAIG immersion gold bath. Part Analysis showed a consistent "level zero" corrosion rating. e final justification for RAIG is for OEMs that have determined that ENIG gold thick- nesses above 4.0 microinches are advantageous Figure 5: Cross-section of corrosion check after 40 minutes of dwell time in immersion Au bath. 30 PCB007 MAGAZINE I OCTOBER 2024