Homebrew PCBs

Actually, it takes a little time for the heat to propagate through the
PCB. With a preheated plate I get very good results, no splattering or
such. You could always put a second plate right next to it for preheat
at a lower temperature if you really need to.

But If you want to drive a profile, of course I agree it's no use
having so much thermal mass.

ST

On Tue, Feb 9, 2010 at 5:40 AM, DJ Delorie <dj@...> wrote:

> It certainly does when you have to control the temperature *change
> rate* as well as the hold temps.  Proper reflow wants a specific temp
> vs time curve, not just a pre-heated surface.  The iron plate can just
> barely heat up fast enough for reflow, and mcu can only slow it down.
>
> If I start with a cold plate, put my board on it, and turn it on, I
> get a pretty good temp/time curve - takes about 3 minutes for small
> boards, or 6 minutes if I add an aluminum plate for large boards (heat
> spreader).  Six minutes is a little long.  I'd rather have an aluminum
> hotplate I can mcu-control that can do a proper temp/time curve.
>
> If you put a board on a pre-heated plate, the flux boils and spatters
> solder (and parts) all over the place.  You really need to heat the
> flux up slowly so it activates and cleans the metal without disturbing
> anything, then dries up before the solder flows.
>
> I also don't want to shock the board by hitting it with that much heat
> all at once.
>
>