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February 2012

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From:
Mike Fenner <[log in to unmask]>
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Date:
Fri, 24 Feb 2012 17:07:50 +0000
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There are a number of "paste conditioning" systems available. I still
contend though that paste is, or should be, a material capable of being
sourced as a ship to line product - no need for inspection, verification or
correction before use.



Regards

Mike 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, February 23, 2012 11:59 PM
To: [log in to unmask]
Subject: Re: [TN] Air Bubbles in Syringes of Solder Paste...

Wow. I learned something new. I never knew such a thing existed.  Thanks.
Bev

-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]] 
Sent: Thursday, February 23, 2012 9:22 AM
To: TechNet E-Mail Forum; Bev Christian
Subject: RE: [TN] Air Bubbles in Syringes of Solder Paste...

Bev, a proper paste centrifuge eliminates the separation of flux, as it
folds the paste back in on itself, and it is properly mixed. That has been
my experience. But a "regular" centrifuge would separate the different
densities if it was not designed to mix as well.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Wednesday, February 22, 2012 8:30 PM
To: [log in to unmask]
Subject: Re: [TN] Air Bubbles in Syringes of Solder Paste...

Steve,
I agree with Paul Klasek's Technet comment of May 22, 1998 where he warns of
the separation of solder and the paste flux because of differing densities
if the solder paste is centrifuged. Of course there is the question of speed
and how long. Mike Fenner? Karen Tellefsen?

Bev

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, February 22, 2012 7:52 PM
To: [log in to unmask]
Subject: [TN] Air Bubbles in Syringes of Solder Paste...

Hi All,

I have a question about syringes of dispensable solder paste. We purchase
10cc syringes of Type-4 dispensable solder paste for work that we do. It's
used much of the time to dispense paste for the stacked capacitors that we
do, much of the time it's for 0402 caps, so the dispensing has to be very
precise.

Recently our operators have complained about the paste, they said they're
having a hard time being consistent with the dots they're trying to
dispense. One of the operators showed me the syringe that she was using, and
I was surprised at the air bubbles I saw inside the syringe. The photos
below are pictures I took under a microscope through the side of the
syringe:

http://stevezeva.homestead.com/AirBubbles.jpg

http://stevezeva.homestead.com/AirBubblesClose.jpg

I can see why she was having trouble. As I said, we buy these syringes
pre-filled, they come to us packaged in a cool pack, and we store them
immediately in the refrigerator until they are ready to be used. They are
taken out and allowed to come up to room temperature before they are ever
attached to a dispenser. We use EFD dispensers BTW.

I looked at the syringes that were un-touched and stored in the
refrigerator, and they had the same sort of bubbles. So our dispensers are
not introducing them, and it seemed like the bubbles were only associated
with one lot of of syringes. There was another lot in the refrigerator that
did not have the bubbles.

So my question is (not being a solder paste vendor), how are these syringes
filled ? Do they centrifuge them to eliminate the bubbles ? I know I did
that in the past when I filled syringes with chip bonder for our Fuji
dispenser, in fact, the centrifuge was sold to us by Fuji. But I'm not sure
about solder paste. How do you go about making sure there are no bubbles in
syringes of solder paste ? Is there anything we can do with the paste that
we have to eliminate the bubbles or should we just send the paste back ?

Steve

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