Also, nothing specific about Koki, but, getting back to the basics
of BGA voiding and solder paste selection (whether lead-free or not) --
Some solder paste formulations provide for more voiding in a BGA
than others. In a few previous lives (which weren't so bad), I ran solder
paste evaluations on good old regular Sn63Pb37 using a test vehicle with
BGA's. Although we were able to reduce BGA voiding by optimizing the
profile on most of the samples, some exhibited more voiding than others.
Some companies (this is not a sales pitch), such as Kester, have
developed solder pastes to help minimize voiding in BGA's. Some have
been more successful than others. Aim, Indium, and Alpha also have
pastes that perform well for BGA's.
I have been most successful in minimizing BGA voids by following the
manufacturer's recommended profile AND... keeping the profile at the
BGA toward the longer, hotter end of the profile spec.
I will also say that I once worked with a solder paste company that helped
us with resolving one problem (slump), but, neglected to share with us the
fact that BGA voids were inevitable with their flux solution. That paste
printed so beautifully. The release from the screen was unbelievable. The
paste brick held it's form for hours...even under 80F/80%RH conditions.
Unfortunately...we had Voids :-(
One last thought and that is...is it possible that the BGA's eutectic balls are
getting toooooo hot and not out gassing properly (boiling?) while trying to get the Lead-free
paste to reflow properly? We haven't started experimenting with Lead-free yet,
so I'm wondering what the Lead-Free Gurus (if there are any yet) think about that
theory?
-Carrie
-----Original Message-----
From: Stolar, Paul W [mailto:[log in to unmask]]
Sent: Thursday, January 02, 2003 4:36 PM
To: [log in to unmask]
Subject: Re: [TN] Koki Lead-free Solder paste?
Rick,
Nothing specific about Koki, but here are some questions. Most times I have
found the solution with these questions.
1. How is the profile measured? (TC in air or embedded in board?)
2. How is the paste controlled? (Is it sensitive to moisture?)
Hope this helps.
Paul
-----Original Message-----
From: Rick Thompson [mailto:[log in to unmask]]
Sent: Thursday, January 02, 2003 3:21 PM
To: [log in to unmask]
Subject: [TN] Koki Lead-free Solderpaste?
Hi,
Does anyone have any experience using Koki Lead-free Solder Paste? In
particular, their S3X58-M301-3 series? We're using this at our Thailand
facility to solder some micro-BGAs and are seeing alot of voiding and
subsequent failures related to the BGA. The balls on the BGA are eutectic,
63/37. Reflow profile is meeting the solder paste manufacturer's
recommendations. Unfortunately, I'm trying to find an answer for this long
distance as I'm not at the facility. If anyone has any experience /
recommendations with this solder paste that they can share it would be
greatly appreciated.
Thanks,
Rick Thompson
Sr. SMT Process Engineer
SMTEK International, Inc.
+1 (805) 532-2800
[log in to unmask]
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