That brings up a good point, Leland.
Steve, why don't you ask the paste manufacturer what steps they have taken to identify the lot numbers of paste that have been affected with the "bad powder" and if they are going to notify their other customers that they would like to recall those lots? I predict one of the following:
1. Their eyes sort of glaze over and they begin mumbling.
2. They will tell you they already have, but they won't look you in the eye when they say it. They have no way of tracing the lots if they sell it on the open market without using only certified distributors. Certified distributors of paste are required to store it properly refrigerated, rotate the stock (FIFO), physically turn the paste over periodically, and monitor traceability to the end customer.
3. They will tell you the problem is isolated to only the tubes/jars you received (which may be plausible if it froze, but unlikely).
That is why I have cautioned on this forum before that you should only buy paste from vendor-certified distributors.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Thursday, January 14, 2010 8:58 AM
To: [log in to unmask]
Subject: Re: [TN] Return of the "Snotballs"
Steve,
Even though you've experienced a problem, it could be much, much worse.
Had we received notification such as yours from our paste manufacturer, we would have had to place all material produced with the lot under Quality Hold, work overtime to re-produce material with known good lots (to keep from shutting down our customer's operations), and start our own set of HALT/HASS testing to prove out the product we'd ran.
In other words, an absolute major headache for everyone because of failure to communicate from supplier to end user.
That kind of stuff can ruin plans for a weekend. Been there and done it many times before...
Leland
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, January 14, 2010 9:27 AM
To: [log in to unmask]
Subject: Re: [TN] Return of the "Snotballs"
Morning All!
Well, we're waiting for a new batch of paste. I was told by the vendor that
they had recently moved, and the company has decided to split their metal
manufacturing (powder, spheres, etc.) off to a separate company. So I was
told that for the interim until this new company gets up and running, they
had purchased powder for their lead free pastes from another manufacturer
and got a bad batch. They told me yesterday that I was not the only one who
was complaining about "Snotballs".
Our reflow profiles are proven, I'm not the only one here who knows about
reflow profiles, those of you that know my boss knows that. Also, the paste
was never frozen in our facility. I can't say that it didn't EVER freeze on
the way here (it's been pretty cold this winter).
Generally, we do not have any problems with this paste. The nice thing about
it is that it is one of a very few that is a halide free, water washable,
no-clean. It's J-STD-004 flux classification is a RELO. The two times that I
have had this issue has been because of a powder problem according to the
vendor. The first time I was told that the personnel who were mixing the
paste were leaving the container that the powder was stored in open allowing
it to oxidize. The said that they were going to re-instruct their people to
avoid the problem in the future. This time they again blamed the powder and
admitted that they had bought powder from a competitor to get them through
the period until the new powder manufacturing facility was up and running.
They said that they were only going to second source powder from a known
good source. We shall see...
We tried the re-fluxing suggestion, and were really surprised by the
results. We used the compatible liquid flux from the same vendor we got our
paste from. It also is a water washable no-clean classified as a ORLO. We
used liquid flux because there are BGA's and QFN's on the board. Capillary
forces were able to pull the flux beneath those parts. This is what the
joints looked like after reflow:
http://stevezeva.homestead.com/After_Flux.JPG
Not too bad looking, huh?
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: Thursday, January 14, 2010 7:27 AM
To: [log in to unmask]
Subject: Re: [TN] Return of the "Snotballs"
Agree 100%. We see this phenomenon on 0402 resnets and some 0402 components
(location specific) on thermally challenging lead-free boards (thick board,
large BGAs, ground planes etc.,) The reflow profile, being tailored to
ensure complete reflow of bigger BGA parts almost always leads to
overheating of the smaller parts and greater than recommended soak times,
resulting in little or no flux activity during reflow. Less flux contained
in the small solder deposits for these smaller parts exacerbates the
situation further.
But the important thing is (leaving aside the appearance part for a minute)
that there is good wetting to the component and an acceptable solder joint
per IPC 610. We have been building these lead-free boards for about 3 years
now and no returns for solder defects related to this condition yet (telecom
application). The process window however, is definitely shortened due to
lower flux activity as now you need pristine parts to be able to get a good
solder joint.
Amol S. Kane
Process Engineer
Harvard Custom Manufacturing, Inc.
941 Route 28
Owego NY 13827
Phone: 607-687-7669 Ext 349
Fax: 607-687-9733
[log in to unmask]
www.harvardgrp.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Wednesday, January 13, 2010 5:33 PM
To: [log in to unmask]
Subject: Re: [TN] Return of the "Snotballs"
Seen worse.........8-(
I have encountered this on a number of occasions and have come to a few
thoughts on the subject.
In my experience it is generally found on the smaller components (such as
0201) and often only on the ceramic parts.
The conclusion that I came to with this is that the flux itself is running
out of steam as the smaller components are experiencing overheating in the
ramp up phase of the reflow profile compared to the larger devices. They
have a smaller amount of solder paste and hence flux, and they are exposed
to the full effect of the reflow profile often in less densely populated
areas. Ceramic also has a very good thermal transfer co-efficient and heat
capacity compared to the other packaging materials such as BAG and other
plastic bodied parts.
The reason that I came to this conclusion is that often you will see this
effect on a small ceramic part but not at all on a QFP or a BGA.
Inevitably in the speed required to "fix" things I instructed our CEM to
back off on the ramp profile and the problem went away. And yes some
soldering materials are less "robust" in this respect.
Sad to say, but I have never seen this condition with leaded
solder...........8-)
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of stephen gregory
Sent: Wednesday, January 13, 2010 12:24 PM
To: [log in to unmask]
Subject: [TN] Return of the "Snotballs"
Maybe some of you remember a post I made a couple of years ago when I was in
Tulsa and I had a reflow problem with a SAC solderpaste. It was then
I learned of a new term called "Snotballs". Here was the picture I posted
back then:
http://stevezeva.homestead.com/files/Snotballs.jpg
Well guess who decided to follow me out to Pennsylvania? Check out:
http://stevezeva.homestead.com/Type_4.JPG
Same vendor, same alloy.
All I can say is make sure you know where your powder is coming from.
Steve Gregory
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