Toaster Oven Soldering for Surface Mounts

[MRW]

Hi all,

I was looking at this website:
http://www.seattlerobotics.org/encoder/200006/oven_art.htm

Has anyone tried this method before?

I was thinking of trying it, but would like some tips such as sources
to get the materials, safety, etc. I've already looked at the Kester
solder paste and plunger on Digikey, but I haven't seen any tips, yet.

I have a PCB ready. Most of my components are 0805 SMT packages, but I
have a a few 0603s. I also have an IC that is a TSSOP package. I
already tried hand-soldering, but I failed miserably. I only have a
couple of parts left, so I'd like an easier but reliable method. If I
had the money, I'd go straight to a local PCB assembly house, but then
again, where's the fun in that, huh?


Thanks!

 

[Erik Walthinsen]

I was looking at this website:
http://www.seattlerobotics.org/encoder/200006/oven_art.htm

Has anyone tried this method before?

Yeah, I've done a few simple boards with it. It works rather well,
actually. Just have to be very careful with the amount of paste you put
on the board, and how close any copper fill comes to the pads
*underneath* the chips. I've been adding restricted zones to increase
that gap after I had a chip or two bridge to the copper fill, which
isn't solvable without completely starting over. (This is on home-made
boards with no solder mask)

Another site, can't remember off the top of my head atm, suggested that
instead of a toaster oven, you use a cheap skillet. I bought one for
~$20 at Target and have had better luck with that so far, at least for
the tiny SMT->DIP adapters I've soldered up so far. A properly selected
one will make fume extraction easier (I replaced the top handle of the
lid with a small rubber tube which I'll be attaching eventually to a
home-built fan exhaust to outside), and visibility is definitely better.
The main advantage is that the heat comes from the bottom through the
board, and is therefore a bit more controllable. The site that
suggested the technique was having problems with USB connectors melting
before the solder did...

I was thinking of trying it, but would like some tips such as sources
to get the materials, safety, etc. I've already looked at the Kester
solder paste and plunger on Digikey, but I haven't seen any tips, yet.

I had to check a local contractor-supply type place to get them. They
came in a box of 50 (disposable) for about $20. Of course you're only
going to use one, and changing sizes is out of the question unless you
can find a way to get all the paste out of the tip that you're switching
out. Go for a rather small one, maybe a metal-tipped one if you can,
with something like a 10mil openning.

 

[MRW]

Thanks, Erik!

From the site I mentioned, it seemed like they put solder paste not

just on the actual pads, but also paste in between the pads. Any reason
why?

Is the paste really easy to get out after you are done "toasting"?

 

[DJ Delorie]

From the site I mentioned, it seemed like they put solder paste not
just on the actual pads, but also paste in between the pads. Any reason
why?

Well, in wave soldering, they cover the whole board with solder. The
trick is, the solder (hopefully) won't stick where the mask is,
between the pads. So, as long as you've put the right total amount of
solder down, it will get pulled to the metal pads (surface tension et
al) once it starts reflowing, and there won't be any between the pads.

You can still do this without a mask, as the solder usually won't
stick to the PCB either, but the risk of bridges increases.

 

[Erik Walthinsen]

Well, in wave soldering, they cover the whole board with solder. The
trick is, the solder (hopefully) won't stick where the mask is,
between the pads. So, as long as you've put the right total amount of
solder down, it will get pulled to the metal pads (surface tension et
al) once it starts reflowing, and there won't be any between the pads.

You can still do this without a mask, as the solder usually won't
stick to the PCB either, but the risk of bridges increases.

In the case of hand-applied solder paste, it's basically impossible to
put an appropriate sided drop on every pad of even a SOIC. Since the
PCB itself will not hold solder, as long as you have a string of it
along the pads of the right thickness, the surface tension of the melted
solder will cause it to ball onto each pin and flow properly.

It's actually very instructed to just give it a try and pay close
attention to the instant when the solder melts (which usually occurs
from one side of the board to the other, not all at once). You'll get a
good feel for the surface-tensionn properties at that point.

A trick for dealing with variable placement of solder paste coming from
the syringe is to shove it around carefully with a sharp dental pick.
If you get a trailing blob off the end of the syringe somewhere, either
pick it up and remove it entirely, or shovel it around to places where
it's not as thick. If you do the chips first, you can move the excess
to the discrete's pads.