Good points, George.
Trouble is, in order for the temperature under a large BGA to reach 220C
for any duration, the rest of the component leads on the assembly will
be close to what? 235C? Not a good process for some components.
The problem with the logic that the ENIG will work better at higher
reflow temperatures seen with Pb-free processes is this:
The plating issues that cause the nickel oxide formation during the
immersion gold step (related to the phosphorus content, amongst other
variables) are exacerbated by subsequent temperature excursions. If the
plating is properly done, then yes, perhaps the IMF formed to nickel
will be more easily accomplished. However, if NOT done properly, the
higher temperatures will make the Black Pad and other nickel plating
process-related problems much, much worse. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of George Milad
Sent: Monday, May 15, 2006 2:15 PM
To: [log in to unmask]
Subject: Re: [TN] Question about ENIG and other surface finishing

I believe one of the key issues in assembling ENIG parts is that the
inter-metallic formed is a Ni/Sn. Ni/Sn inter-metallic requires  higher
peak assembly temperature and a longer dwell at peak temperature. The
right  re-flow temperature profile is a must.

The recommendation of ENIG assembly is 220 C for 20 seconds.

Some of the failures with ENIG may be attributed to colder assembly
temperatures.

The transition to Pb-Free should favor ENIG as the assembly temperature
for Pb-Free is going to be higher and the Ni/Sn inter-metallic will
always be formed  successfully.


Best  regards

George Milad
[log in to unmask]
National Accounts Manager  for Technology Uyemura International
Corporation Technical Center 240  Town LIne Rd Southington CT 06489
(516) 901 3874 (mobile)
(860)  793-4011 (office)
(860) 793-4020 (fax)

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