Joe, I have seen the "it depends" notes...............8-) 

........and of course they are correct, the finish, the re-work process, the
component being re-worked will all contribute.

One thing though - how many times do you need to rework it for your
purposes? 

I have seen load board designs which were purposely build to withstand many
(10+) rework operations on BGA's using enig as a finish (here the component
could not be socketted for DVT testing purposes).

The issue there was actually not the enig, but how to keep the solder resist
in place with a BGA design during multiple re-work in the "dog bone" area
between the pad and the via.

If you need data on that contact me off line.

Have a great memorial day weekend Techies.............

John

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Macko
Sent: Friday, May 23, 2008 10:41 AM
To: [log in to unmask]
Subject: [TN] Methodology for determining the # of reworks ENIG finished
solder lands for leaded components can withstand

Techs,

 

I am looking for some help / guidance on how to analytically determine
the number of times the same leaded component can be replaced on a ENIG
finished board before the solder lands located on the PCB have been
degraded beyond their capability to provide a solderable class 3 surface
(.e., how many times can the ENIG finished solder lands with stand a
rework/component remove & replace).  I suspect the dissolution rates of
nickel and copper come into play however I am not sure how to approach
this issue and suspect there are some relatively straightforward
formulas out there to accomplish this task. Everyone has a different
idea and there are numerous rules of thumb discussed but I would like to
try something more analytical (without having to use a supercomputer).
Thanks again and everyone enjoy the long weekend.

 

Best Regards,

-joe

 


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