Dear Lee,

why do you need lower phosperous content ? to process boards at lower temp
than what is recommended by chemistry supplier.
Nickel has crystalline structure at low phosphorus content (upto 3 to 4 % P)
hence gets tarnished /oxidises very easily. If you use low phosphorus EN, then you may need an activator between EN and IG which often may not work satisfactorily.Result gold peeloff if you do tape test.
Normally the chemistry supply EN for ENIG finish with P content between
 8 to 10 % . also while operating the bath the phosphorus content varies depending on PH and reducer.

normally we  bake boards at 140 C to check for tarnishing of Gold. The gold 
does not tarnish if you put sufficient gold and it works.

radhakrishnan
indal eletronics
india

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