HI Steve
If previous batches have been satisfactory and now you have one which is not
then........ certainly you should take it up with your supplier. It would be
unusual these days to have to check or rectify solder paste before being
able to use it.
If you are desperate to use the paste to avoid a line out or something you
could as suggested try tapping the syringes in a vertical position. Be
patient/persistent. I am uncomfortable with customer centrifuging, there is
the risk of damaging the paste, and anyway see above.

To answer your questions:
Different suppliers will have their own procedures for filling syringes. You
could expect that de-airing the paste (most likely by a vacuum pull) would
be in the process. A common method for syringe filling is backfilling.

Comment:
Whether or not your supplier recommends vertical storage of the syringes, I
suggest you might wish to do so. Also take care not to cycle the syringes in
and out of the fridge as - depending on the size/syringe material type - you
run the risk of drawing air in. 
If you are using timed pressure dispense systems you might want to consider
ordering part filled syringes. This will improve precision of dispense by
reducing the difference in dispense behavior from first to last caused by
the increase in air volume in the syringe as it empties.
It will also reduce the possibility of separation by reducing the number of
on off pressure cycles the paste is subjected to. (more important/beneficial
for some suppliers than others)


Regards

Mike Fenner 
Bonding Services & Products
T: +44 [0] 1865 522 663 E: [log in to unmask]

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, February 23, 2012 12:52 AM
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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