Torrid time with syringes & solder paste.

Community PCB Design
1

Hi guys,

Ok, so last year I bought a paste dispenser from China…at the same time I bought some solder paste in a syringe on Ebay.

I didn’t get around to using it until about a month ago - the long & short is that the paste didn’t flow.

I then realise that it had probably long expired, wasn’t kept refrigerated etc.

So i read about the success of Deal Extreme soldered paste- ordered some…grew a beard waiting.

Alas, they don’t sell it in syringes, so when it arrived, I scooped out a ‘dollop’ into the dispenser syringe - hey presto …it worked (ie flowed)…but wait. It only worked the one time! ie…since then, it’s not reflowing (just a grey hard crud - which is not the end of the world, but annoying - all I do in this case is simply take a soldering iron to the hard crud & it flows well)

So to my questions…

  1. If the paste is in a syringes, I’d have thought it’s fairly ‘air’ tight (bar the tiny bit exposed at the nozzle)…so how come it’s going off so quick.

  2. Is there anyway of rejuvinating paste that isn’t flowing, because this is gonna get costly quick! (I’m thinking here along the lines of adding in some liquid flux)

Also, for any of you guys using a solder paste dispenser…what type of nozzle are you using? (metal needle type…or plastic nozzle - I bought some from Deal extreme too - but not having great success with them)

2

peskywinnets:
…what type of nozzle are you using? (metal needle type…or plastic nozzle)

I've used the "needles" from inkjet refiller kits - they work quite well, and fit normal syringes.
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peskywinnets:
2. Is there anyway of rejuvinating paste that isn’t flowing, because this is gonna get costly quick! (I’m thinking here along the lines of adding in some liquid flux)

In a real production environment, it’s a bad practice to add flux to solder in order to make it “print” better. You start to add variables to your reflow process which can result in lots of rework. Fresh solder paste is a lot cheaper than paying the labor involved to rework a batch of boards.

On the hobby side of the argument, you can certainly add flux to your paste in order to make it flow through a syringe. Since there are all different kinds of solder pastes and stand alone flux, I would experiment with a few different fluxes in small batches (if available) to see what works best for you.

-Bill

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These folks have tips in all sizes. They are in CA and ship fast.

http://www.zeph.com/zephpaste.htm

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peskywinnets:

  1. If the paste is in a syringes, I’d have thought it’s fairly ‘air’ tight (bar the tiny bit exposed at the nozzle)…so how come it’s going off so quick.

I always take the tip off mine when I’m done, clean it out, and put the cap back on the end of the syringe (my original syringe of solder paste came with a cap). I’m using tips from zeph.com. As soon as I settle on a tip that I’m happy with (I bought the assortment), I’ll probably just order a bulk pack and start throwing them away when I’m done.

I’m also using one of those chinese pneumatic dispensers. Seems like a pretty good bargain for all that it does.

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I leave the needle on my syringes. I take a thick piece of stripped insulation from scrap wire, screw a small screw into one end and slide the other end over the needle. Makes a nice tight seal and keeps everything “moist”.

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Different brands of paste seem to have wildly different shelf lives, I’ve found that EFD Solderplus last for years, others dry up in a coupel of months. With stuff that comes in syringes I suspect it also depends how good the rear seal is at keeping air out.

I use stainless dispensing needles - these clog less easily than the tapered plastic ones - I get them from ebay as they can be hard to find in small quantities elsewhere.

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Thanks for the replies - I guess I’m just going to have to find a better storage method.