I am looking for references,relevant to the reliability of 
sn63/pb37 solder joints, when used in conjunction with an electroless 
nickel / immersion gold finish, applied (over copper) to PCB's. Pull 
strength of the solder joints, is also of interest.

Note:	Electroless nickel thickness :- 4 to 8 um
	immersion gold thickness     :-	0.03 to 0.07um

	My particular interest, is the solder joint reliability, when 
subjected to  thermal shock, thermal cycling, (-50c to 100c) 
vibration & high humidity levels.

	Most of the nickel/gold process suppliers are listed below :-

Lea Renol
Shipley
Elf Atotech (or Atochem)
Mac Dermid
Technique

	We have information from most of these companies, but they 
tend to concentrate on solderability. The only relevant article I 
have managed to find, is by K.Banerji & E. Bradley of Motorola, 
titled, "Manufacturability & Reliability of products assembled with 
new PCB finishes".(SMI proceedings '94)
	The article mentions crack propagation at the nickel / tin 
intermetallic layer, when assemblies are subjected to mechanical & 
thermal shock. The Authors appear to have concluded, that the nickel 
/ tin intermetallic is weaker, or more brittle, than a copper / tin, 
intermetallic. The phosphorous content of the nickel is also thought 
to cause problems, as it is "displaced ahead of the growing 
nickel/tin intermetallic & forms a layer of a complex compound, that 
causes degredation of interface strength"!
	Is there any informaion that can substantiate (or deny) this 
report?

Regards
Kevin Berry

Radstone Technology Plc
Waterlane
Towcester
Northants
NN12 6JN

Tel:   01327 359444
Fax:   01327 358100
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