Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

solder paste

Views: 10717


solder paste | 8 December, 2009

How do people prepare there solder paste for screen print?

We currently remove them from the fridge and mix them in a 500g solder paste tub mixer to mix the flux and paste together

we waste to much paste at the moment as we only use the tub for 1 build (high mix low volume)

im looking to move over to 6 0z cartridges and air supply and gun to apply a small bead on the stencil, my problem is the paste mixer for the cartridges. I can only find one available the Malcolm sps-5 anyone have any other examples?

reply »


solder paste | 9 December, 2009

Sorry i wasnt very clear we already have a Malcolm sps-1 for our tubs but to move over to cartridges we need a machine to do that none of those machines are capable of mixing a 6 oz cartridge

reply »


solder paste | 9 December, 2009

I am curious as to why you need to mix.... We use a 500g cartridge with air gun. Our process is remove the cartridge from the fridge, allow it to warm up to room temperature before inserting into air gun, then apply bead of paste to the stencil. No mixing because the paste already has the flux built/mixed in.

We do this with both no clean and water soluble type fluxes and both lead and lead free solder. The paste will start to dry out and then not flow/spread properly in our stencil printer if it is old enough to exceed the expiration date and not keeping the unused portion in the fridge will shorten the shelf life as well. As long as we have watched those factors closely we have not had any problems.

reply »


solder paste | 10 December, 2009

do you not have a problem with flux seperating from when it was chilled?

due to our high mix low volume we really cant afford to have solder paste waiting for an hour or so till its ready before we can build

reply »


solder paste | 10 December, 2009

Just how cold do you store your paste?

And what are your solder paste reps like? Here they fall over each other giving support for their paste.

And have you seen the problem with flux separation or have you only heard about it?

reply »


solder paste | 10 December, 2009


Dyoungquist is correct. You should not need to mix solder paste. Overmixing solder paste can adversely affect it. Follow these guidelines and you should be fine:

1. Keep unopened containers of paste in the refrigerator. 2. Take one container out and allow to stabilize to room temperature. Again, mixing is not required. 3. After use, DO NOT return the opened container to the refrigerator, as condensation may occur. 4. Cover and keep the opened container at room temperature and use until empty. Do not use if it gets crusty. Alternatively, we have not had any noticable problems mixing in a little liquid flux (same type) to the paste if it dries out too much. 5. The paste we use is good for a year at 70 degrees F conditions. Yours may be similar, so leaving it at room temperature should not be a problem for at least a few weeks. 6. Store your cartridges in the refrigerator vertically, not horizontally. Storing them vertically will minimize flux separation. No recommendations on the tubs, though.

Hope this helps!

reply »


solder paste | 10 December, 2009

We've used mostly cartridges for many years and I only saw separation once when a particular paste supplier had a problem. With cartridges it's just thaw and use - no mixing. We have some sites that use jars along with mixers and I've never been comfortable with them. The mixing has to be done in a very controlled way or the paste can be overheated. Every supplier I've talked to cringe at the idea of their customers using mixers, although they understand the reality of some customers not wanting to wait for proper thawing.

reply »


solder paste | 11 December, 2009

I won't say never but very rarely do we have problems with the flux seperating.

The way we get around the 1-2 hour warmup time is this: The day before we run a particular job, the last person takes out the paste needed from the fridge as the last thing they do before they go home for the evening. The paste then warms up overnight and is ready for the first person who comes in to start using it right away the next morning. If the job requires more than 1 day we leave the paste out overnight, as there is no need to cool it down for that short of a period.

reply »


solder paste | 14 December, 2009

why not use a paste where it requires no refrigeration at all cheers Greg

reply »


solder paste | 15 December, 2009

Which paste are you referring to?

reply »

SMT Spare Parts and Feeders

ICT Total SMT line Provider