47310Re: [SeattleRobotics] SMT toaster oven problems
- Oct 25, 2012From: "Tony Mactutis"
> Peter, I don't think the solder paste would go bad in a few months if itThat's good to know.
> has been in the fridge. I've used much older paste than that.
> There may be scattered beads when you are done;Yes, that's how it used to be. But now there's too much grey goo.
Same solder, same oven. And I think the same profile.
> I would make sure to leave the board in the oven until all the solder isThat's pretty much what I do except that I _do_ worry about the profile.
> melted. Don't worry about the profile. I just turn my oven up all the
> way (the dial goes up to 500 F) and wait for it to hit temperature. I
> then put the board in and wait for the paste to melt. When it has all
> melted (maybe 4 to 5 minutes), I give it perhaps 20-30 seconds and then
> take the board out to cool. No timing required.
The oven has an aluminium tray that I sit the board on, a bottom element
below the tray and a top element above the tray. I turn on the lower element
for a couple of minutes to pre-heat the board. The aluminium tray nicely
spreads the heat evenly. Then I turn on the upper element as well until the
solder melts. Then leave it another 20 sec. Then turn off and open the door.
It used to work just fine.
From: "Randy Carter"
> The aging factors in solder paste are the solvent in the flux evaporatesIt was sold as a 50ml syringe of solder. So it's always completely sealed
> and the solder corrodes. The solvent evaporating is slowed by
> chilling the container.
apart from the very tip of the needle. I don't see how it can evaporate or
oxidise other than _through_ the plastic barrel. Which is unlikely. Right?
> The corrosion of the solder is going to make it a little more difficult toWell, I tried more time. All that happened was that I over-cooked some of
> solder. Requiring a little more heat and time.
(I can't turn the temperature up any further.)
I wonder it I'm not ramping up the heat fast enough or I pre-heat for too
long. Maybe the flux has all evaporated before I turn the oven up to
solder-melting temperature. That way, the solder can flow together into a
> Also you may be using too much paste.Could be but I don't think I'm using more that I used to.
On the pads with too much paste, the solder used to ball-up. Now it doesn't.
> The process I use is to heat the board to 95C for 30 minutesI don't think that's a problem with the chips I've been using.
> to chase out any moisture
We just got some accelerometer and RTC chips which came with big warnings
about "use within 160 hours of opening the package". I haven't tried
soldering them yet.
> Then I crank it all the way up and wait until 220C is reached then I turnAha. So it's a quick up and down. Not a long pre-heat that might destroy the
> off and open the door,
> I do have a fair amount of solder balls stuck to the boardYes, I used to get those. As you say, they're no big deal.
> that are easily knocked off with a pick.
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