No it doesn't. BP is a time-variable defect.
But I agree that it probably isn't BP, more likely a CTE mismatch issue
due to improper cooling. However, it can be both. The pad cratering has
nothing to do with BP or vice versa.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Igoshev, Vladimir
Sent: Wednesday, June 18, 2008 12:37 PM
To: [log in to unmask]
Subject: Re: [TN] [LF] [TN] SN100 for Reflow Application
Not at all. The fact that you also got cracks in laminate rules out BP
:-)
Regards,
Vladimir
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: Wednesday, June 18, 2008 12:51 PM
To: [log in to unmask]
Subject: Re: [TN] [LF] [TN] SN100 for Reflow Application
Dear Valdimir,
Can you please clarify your E-mail below? Do you think I may be dealing
with black pad?
Regards,
From: Igoshev, Vladimir [mailto:[log in to unmask]]
Sent: Wednesday, June 18, 2008 10:55 AM
To: [log in to unmask]; Kane, Amol (349)
Subject: Re: [LF] [TN] SN100 for Reflow Application
Hi Amol,
The thickness of intermetallic layer does not indicate whether you might
deal with BP or not, but the fact that you got laminate cracks does.
Regards,
Vladimiir
----- Original Message -----
From: Leadfree <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Wed Jun 18 10:33:12 2008
Subject: Re: [LF] [TN] SN100 for Reflow Application
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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