It does not take anything very special to do reflow on PCB's. The last place I worked I used a cheap toaster oven and soldered several hundred prototype surface mount boards. I measured the temperature profile, and it heated up and cooled down at close to the rate used by real reflow ovens. I simply used a syringe and needle to deposit small amounts of solder paste (Tin-lead solder, before ROHS) on the pads, or a line of paste on IC pads. The components were then placed on the board by hand close to the location where they belonged. A group of 5-6 boards was placed on the rack of the oven, and the thermostat was turned to maximum. The oven was turned on and I observed the boards through the window. When all the solder paste melted, easily seen as a change from black to molten solder, I allowed about 15 seconds to soak, then shut off the oven. I let it cool for about 5 minutes, then removed the boards. All the components were pulled into alignment by the
surface tension of the molten solder, and the excess paste between pads migrated onto the pads, so we had very few solder bridges. Once in a while a component would "tombstone" if it did not have enough paste on one pad, but it was easy to fix with a solder iron.
We were working mostly with 1206 and 805 size components, with 0.050 pitch ICs, and if we had a double sided board, it only had a few components on the backside, which we hand soldered. For very fine pitch it could be more difficult, and the ROHS solder may not work the same. Note that for this to work correctly you need solder mask between pads and traces, otherwise the components may be pulled out of alignment unless glued down first, which is often done for double sided boards.
I would be concerned about the hot air wedge in the pizza oven. If the airflow is too high, it might blow some components around before the solder has time to melt. I never tried a hotplate, but see no reason it would not work the same. You can often find toaster ovens at thrift stores for a few bucks. Just don't use them for food after melting solder.
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From: Stefan Trethan <stefan_trethan@...>
To: Homebrew_PCBs@yahoogroups.com
Sent: Friday, September 2, 2011 11:12 AM
Subject: Re: [Homebrew_PCBs] Pizza Oven - is this possible
There was a discussion about pizza oven reflow some time ago, look in
the archive.
But it was another type where the pizza rotates through a hot air "wedge".
As you say any type of oven can work if sufficiently hot, which it
really should be to make a pizza.
I also prefer a hotplate for SMD soldering, heat transmission through
the PCB is much more even and consistent than radiant heat. Also
components can be tweaked during reflow. Doesn't work so well for
double-sided boards of course.
That reminds me - I should soon have a look at that plum cake in the oven.......
ST
On Fri, Sep 2, 2011 at 5:55 PM, Peter Harrison
<peter.harrison@...> wrote:
> Hi
>
> I was looking around a local store and came across a tabletop pizza oven:
>
> http://www.argos.co.uk/static/Product/partNumber/9331897/Trail/searchtext%3EPIZZA.htm
>
> They are reasonably cheap and should have room inside for about 6" diameter. Has anyone tried reflow with one of these? I guess that, so long as it can get up to about 240 deg C inside it stands a chance but I am not so sure it could get that hot. Certainly, I am not sure enough to try buying one just to see.
>
> It would be nice and compact though. Maybe replace the thermostat…
>
>
>
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>
>
>
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