No Farnell probably couldn't care less how long the paste keeps after
you opened it, i bet they just stock it like all their other stuff.
The Edsyn CR44 seems to keep far better than other types. I've
continued to use the same dispensing tips after many days of storage
in the fridge (tip separately from capped syringe, just in case i
don't need it for an extended period of time).
But i've also left the used dispensing tips on the bench and they were
just fine next day. With other paste they were dry and clogged after a
few hours.
Anyway, i'm fairly sure this paste could keep well at room
temperature, but i still put it in the fridge (in a zip-lock bag,
together with the tip).
Of course there's a drawback too. The CR44 is just about the worst
paste i have ever used in regards to reflow behavoir. The stuff
softens like butter as soon as it gets hot, and builds huge puddles on
the PCB. Any other paste i ever used (apart from plumbing paste ;-) )
was far better in that regard. A SMD paste should "keep shape" under
heat until reflow. This would also keep the components in place better
(with CR44 i have more that misalign).
Maybe one day i will find a paste that has both, decent shelf life
(fridge shelf is OK with me), and decent reflow properties. But until
then i prefer to stick with a paste that still comes out of the
syringe when i need it, even if the reflow properties are rotten.
Too bad i didn't think to ask, had a rep. from a soldering tool
company visiting this week.
ST
On 4/23/08, Dylan Smith <dyls@...> wrote:
> Hi list,
>
> For the first time today I used solder paste. Much nicer way of soldering
> fine pitch SMD - using the soldering iron to do it was getting old rather
> fast. My method was to lay down a bead of paste on each row of pads, place
> the chip, then use a hot air gun. It was nice not to have to spend 15
> minutes carefully lining up a big LQFP then bodging it when trying to tack
> the first pin and starting again. I had read that the component will try
> and centre itself thanks to surface tension, and this turned out to be a
> good tip.
>
> My main problem at the moment is putting down to much paste rather than
> too little... but I had far less solder to wick up after soldering than
> doing it by hand and the result is much neater.
>
> The paste I got is Edsyn CR44 - it seemed reasonably easy to apply. I
> bought a syringe of the stuff.
>
> What's the best way of making the solder paste keep for as long as
> possible? I had heard that it had to be kept refrigerated, and that it
> would only be sent same day frieght and all this sort of thing but as far
> as I could tell, Farnell didn't treat the order any differently than any
> other component (it certainly didn't go with any priority - took 2 days to
> get to me!)
>
>
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