Hi Steve - based on your pictures, I think Bev has the correct assessment 
- I don't think those are air bubbles but you have flux separation in the 
syringes. Flux separation is an indication of incorrect syringe filling 
parameters or damaged solderpaste. I recommend you contact your 
solderpaste supplier and request replacement of the entire lot.

Dave Hillman
Rockwell Collins
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02/22/2012 06:51 PM
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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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