Carrie,
I've had similar experiences with the amount of voiding using different
solder pastes. Since I'm not familiar with Koki at all, that was one area of
concern that I'm looking into. The fact that it's lead-free is also new
territory for me. According to both the paste and component manufacturer's,
the parts and paste are compatible with the higher temperatures of the
lead-free process, but I don't currently have any data to back that up from
our assembly facility.
Slightly off the subject, would you mind sharing with me (offline) what
Kester paste you found minized voids? We currently use a Kester paste for
everything else, but won't use it on boards with BGAs due to excessive
voiding.
Thanks,
Rick Thompson
Sr. SMT Process Engineer
SMTEK International, Inc.
+1 (805) 532-2800
[log in to unmask]
===== Original Message from [log in to unmask] (TechNet E-Mail Forum.) at
1/02/03 2:01 pm
>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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