David
There is differences on the profiles (RSS & RTS) What is the settings for
the LSP profile?.
My next question is. the results are base on a water soluble paste, would it
be different for the NC293?.
thank you
-----Original Message-----
From: David Suraski [mailto:[log in to unmask]]
Sent: Wednesday, January 28, 2004 8:44 AM
To: [log in to unmask]
Subject: Re: [TN] PBGA Void/pin holes
Dear Luis,
I am going to briefly discuss voiding from our perspective. For additional
information I encourage
you to visit our more detailed article on this topic located at
http://www.aimsolder.com/techarticles/tech%20sheet%20BGA%20voiding-%20reduci
ng%20through%20process%20optimization.pdf
There is still a debate as to the negative effects of voids. In general,
large voids that take up a
high percentage of the volume of the joint are considered problematic.
These voids are more likely
to have a more significant effect on the mechanical integrity and heat
dissipation ability of the
solder joint. Smaller, evenly dispersed voids that take up a lower
percentage of the volume of the
joint are often considered "normal" and non-problematic. I'm sure that
others can comment more on
this.
Voiding can be impacted by the materials in use as well as the SMT process.
In our experience
voiding under BGAs can be significantly reduced through process
optimization.
Handling- If BGAs are not stored and handled property a variety of
processing defects can occur,
including voiding and popcorning. The key is to follow the manufacturers
recommendations regarding
moisture levels, baking, storage time, etc. A common practice is to bake
BGAs and vacuum seal them
with a bag of desiccant in a Mylar bag.
Printing- BGA solder defects are often traceable to the printing operation.
If the printing is
mis-registered, or if the volume printed is insufficient, it is likely that
the resulting BGA solder
joints will not have the desired integrity. For this reason, it is
imperative that printing
equipment be properly calibrated, set-up and verified. 100% inspection of
printed BGA sites may be
required prior to placement to verify paste coverage, uniformity, and
volume.
Reflow Profiling- Two types of reflow profiles are most commonly utilized
when reflowing SMT
assemblies: Ramp-Soak-Spike (RSS) and Ramp-to-Spike (RTS). Optimizing these
profiles per the solder
paste manufacturer's guidelines can help to reduce voiding. In addition,
one can also utilize the
"LSP" (low soak profile) profile, which has proven to significantly reduce
voiding when used in
conjunction with several types of BGA components. The success of the LSP
profile lies in its
ability to dry out the solvent of solder paste before the reflow zone. I'll
be happy to send
additional info on the LSP profile to you if you like.
Regards,
David Suraski
[log in to unmask]
AIM
+1-401-463-5605
www.aimsolder.com
> -----Original Message-----
> From: Luis Gallegos [mailto:[log in to unmask]]
> Sent: Monday, January 26, 2004 10:02 AM
> To: [log in to unmask]
> Subject: [TN] PBGA Void/pin holes>
>
> Good morning Technetters.
> I am having some occasionally voids/pin holes on our PBGA. We are
currently
> using NC293 Sn63/Pb37 Aim solder paste. The board is silver plated.
Printing
> with a 6 mil stencil.
> Is it normal to have occasionally voids?
> We have bake our PBGA's prior to reflow, and also work with the oven
> profile. Any suggestions.
> Thank you
>
> Luis A Gallegos
> Automation Senior Technician
> SANMINA-SCI
> Pleasant Prairie WI
> Phone: 262 947-7700
> [log in to unmask]
>
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