Pete,

Thanks for posting the link to the Atotech paper on how the black pad
condition depends on the phosphorus content of the electroless nickel
layer. I have been reading, off and on, about black pad for years now
and this paper, which is short and easy to read, makes by far the most
sense of all that I have read. 

I am encouraged that the authors can propose a simple test that allows
the board fabricator to monitor whether the phosphorus content in the
nickel is high enough to resist attack by the immersion gold plating
bath. That fact, assuming that fabricators use this test, makes me
willing to reconsider my strongly negative opinion of this finish.

The paper did not address brittle interface fracture. Am I right in
saying that the development of phosphorus-rich layer between the nickel
and the solder as you describe is the cause of BIF, and that apart from
the fact that it occurs with the same finish is unrelated to black pad?
If this is so, then I would think that a high phosphorus content in the
nickel would not be beneficial as it is for preventing black pad. But at
least, susceptibility to BIF is a condition that can be tested for
rather easily. 

I still wonder whether it is possible to deposit an ENIG finish that is
not susceptible either to black pad or BIF, and if so, how readily the
deposition can be controlled day in and day out.

 

Gordon Davy 


-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-------------------------------------------------------------------------------