Hi Pete,
We will not be using the DICY cured laminate in a LF process. It wont withstand LF process temperatures. yes, we did observe a P rich area and a rough Ni surface. However, a presence of a thick intermetallic layer rules out black pad. it does reflect a plating bath that Is potentially unbalanced wrt the chemical composition. However, the SnPb version of the board is also ENIG and from the same board supplier. Therefore all things being equal (plating wise), we see cracks only with the LF assembly.

All the obvious SMT process steps (Solder deposition, solder ht, reflow temps etc.,) were checked to ensure accuracy.

Regards,
Amol


-----Original Message-----
From: Pete Houwen [mailto:[log in to unmask]]
Sent: Wednesday, June 18, 2008 9:53 AM
To: [log in to unmask]; Kane, Amol (349)
Subject: Re: [TN] SN100 for Reflow Application

Amol,

If you are joints that much more prone to failure, don't rule out your process
just because they aren't failing during the process.

Are these ENiG plated boards?  When you did your cross sections, did you do
any analysis of the interfacial?  Are you getting P-enriched zones?  Are there
voids - large or micro, in the joints or balls?  Are the soldermask openings and
registration the same on both versions?  Do you inspect the paste deposition
to make sure the stencil is releasing the lead free solder as it did with tin/lead?

While the fractures aren't showing up until you apply mechanical stress, the
process itself could be weakening the joints, and that doesn't always show up
on all of the balls, or even the same ones consistently.  Though pad cratering
indicates that at least at those pads, the joint was stronger than the laminate.

Be careful using dicy cured epoxies with lead free process temperatures.  A
whole 'nother can o' worms.

Pete




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