Issue link: https://iconnect007.uberflip.com/i/992528
JUNE 2018 I PCB007 MAGAZINE 29 autocatalytic plating, as there are no exchange electrons available. The mass determined by the QMB is then compared to the ICP value from SET1 to determine a value for autocata- lytic reaction in % (Figure 3). The evaluation showed that the reduction- assisted immersion gold does not perform au- tocatalytically and that the SA-Au is only semi autocatalytic (Figure 4). An Example of the Benefit of Autocatalytic Electroless Gold Characteristics in Production Whilst establishing the autocatalytic char- acteristics of a gold bath is of interest for un- derstanding the mechanism, the results have no meaning unless an analogue impact can be related to production. This section of the ar- ticle will focus on the issues from fabricators who request thick gold and employ the EN- EPIG process. Multiple final finish layers increase the risk of anomalous failures. Though uncommon, pinholes are a recognized failure mode (the name may vary by region). It is not the aim of this article to establish the root cause of this phenomenon, but to use the failure to show- case the benefit an autocatalytic process. Pin- holes are plating failures that increase the po- tential for corrosion incidents (Figure 5). Reduction-assisted immersion gold is a suc- cessful product in the market. However, the immersion process relies on electron exchange mechanism which under some conditions can translate to corrosion. Corrosion refers to ex- cessive localized electron exchange (Figure 6). Figure 3: How SET 2 is used to determine the autocatalytic % of a gold bath. 4 0 10 20 30 40 50 60 70 80 90 100 RA-Au SA-Au % Reaction % autocatalytic % immersion Figure 4: The results according to the evaluation method used. Figure 5: View of pinhole from top surface. Figure 6: Cross-sectional view of corrosion by the RA-Au.