I looked at the pictures of the syringes. Since I don't deal with solder paste at all I was intrigued, it looks to me like the filling unit for the syringes has the paste under slight pressure with possibly an air or inert gas blanket, that gas is being infused into the paste by the laws of partial pressures. When the paste is dispensed into the syringe and sits over time the gas diffuses out of solution as the internal pressure decreases, my guess. The other possibility is that air or gas is in the mix and is absorbed into the paste but then diffuses out due to changes in atmospheric conditions.
We see this with instrument lines in the process, when we fill and vent the lines not all of the air is removed and as the systems press up the indications normalize once the air is dispersed into solution. Again when the system is depressurized the entrained air is released from solution and my cause erroneous indications as the bubbles combine to displace the liquid in instrument lines.
I would imagine that if the syringes were stored under pressure the bubbles would go away.
pat
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Friday, February 24, 2012 10:06 AM
To: [log in to unmask]
Subject: Re: [TN] Air Bubbles in Syringes of Solder Paste...
Mike, I totally agree with you. Unfortunately, not all solder pastes (brands, types) are ready for production use when received. The ones that are, are not always optimal either. Therefore the conditioning methods ensure the paste is properly mixed, is at the optimum viscosity, and there is no separation of the flux from the rest of the paste ingredients (spheres, thickeners, etc.)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Friday, February 24, 2012 11:08 AM
To: [log in to unmask]
Subject: Re: [TN] Air Bubbles in Syringes of Solder Paste...
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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