Just another datapoint... my setup is:

4-element 1500W toaster oven with convection fan.  I get good results 
with this.  I recommend spending a bit of $ for something good.  Mine is 
a Delonghi referb from ebay for $50.

The temperature settings and thermometer display (if any) on the oven is 
more than worthless, it may cause you to really overcook boards.  I 
spent $30 at jameco for a cheap meter with thermocouple.  Much much better.

Parts are sturdier than you think.  Just don't be on the super hot for a 
long time.

Haven't tried lead-free, and probably never will as long as leaded is 
available.  Just doing minor rework on lead-free boards made at a CM 
shows how much hassle it is.  Lead is great stuff.

Be mindful and wash your hands.
Goes without saying to never use the oven for anything but boards.

I keep the paste in a mini fridge in a tupperware container, and I keep 
food in the fridge as well.  I don't see what the problem is, but I'm 
also careful.

I use syringes as well as stencils to place the paste.  Syringes work 
well but after awhile your hand starts hurting from having to maintain 
pressure.

For both syringes and stencils, my problem remains solder bridges on 
tssop packages.  0402 and soics and whatnot are almost always fine.

For cheaper stencils, get mylar at pololu.com.

I just got my first metal stencil ($99) and a $200 holder for stencils 
at stencilsunlimited.com.  A big improvement, but I can tell I'm going 
to get some tssop bridges on 3 boards I'm doing at this very moment, and 
aligning the stencil to the board remains a pain.

Once you start down this road, I recommend a hot air SMT rework station, 
it is great if ICs wind up being askew, you can just heat them and 
remove cleanly.  I got mine for $150-ish at circuitspecialists.com. 
Highly recommended.  You can place parts faster and be less 
fussy/worried when you know you can just pull them if there is a problem.

My "reflow profile":
heat to 100deg C for a minute or two, to get everything relatively 
evenly warm.
then heat to 200deg C or so over a minute or so; watch the solder paste, 
it will melt in a slow wave, usually back to front of the oven.
when the paste in the front has melted, I usually let it go up another 
5-10deg over 10 seconds.
then I turn off oven, crack the door an inch, and wait for cooldown.

Works pretty well all told.
Have a magnifier and I suggest really skinny solder braid - I have some 
0.025" stuff, mg chemicals #423 from digikey.  Recommended.

If you have big metal parts (like a large inductor) the paste for it is 
what you should watch, it will melt last, and the warmup and 200deg C 
times may take longer because of its thermal mass.  Or: don't try to do 
it in the oven, just do it by hand later.  I haven't yet had a problem 
but a friend did.

And there you have it, a summary of a fair amount of experimentation.

Improving things to get tssop paste to be the right amount consistently 
and without a lot of fiddling of the stencil is the next important step. 
  I may spring for a kilobuck+ stencil holder system to solve this, some 
research is necessary here.

BTW, I'm making three boards with ~400 SMT parts on each right now, and 
have no real concern about the baking process or damage.  There's 12 
tssops and approx $400 in parts on each.  You just have to really 
inspect the tssops and use current limited power supplies for the 
power-up moment.

Good luck, it is fun but sometimes tedious...
J



solarwind wrote:
> I recently read an article on the Sparkfun website regarding reflow
> soldering for surface mount components that can be done at home on any
> form of hot plate (stove top frying pan, skillet, etc...).
> 
> I have several questions regarding this (that were unanswered in the
> article, and for which I was unable to find answers on the Internet).
> 
> * I thought heat damages components. I was consistently cautioned not
> to overheat components during hand soldering. If the idea is to heat
> up the solder just enough to melt (and maybe a bit more so as not to
> form a "cold soldered" joint), then wouldn't reflow soldering do the
> same damage to components?
> 
> * One of my DIP chips came with a notice saying that it should be
> "cooked" at 125 degrees Celsius prior to reflow soldering. I would
> never reflow solder a DIP chip, but this is interesting. Why do they
> have such requirements? Is it because of any possibility of trapped
> moisture in the chip that could rapidly expand in high heat and damage
> internals? What's the worst case for not obeying this notice?
> 
> * I've also heard of reflow soldering "profiles". What exactly are
> these profiles? Is it a requirement that I adhere to them for homebrew
> reflow soldering projects?
> 
> * How do I apply solder paste on pads? Do I just squeeze it out of the
> tube and rub it consistently over the pads so that all of it is
> connected? Does a very precise amount need to be applied discretely on
> each individual pad? How is this done?
> 
> * Where to buy solder paste, are there different types, what brand,
> what type? Should I use flux? Should I pre-flux the pads or apply flux
> and then solder paste?
> 
> * I've also heard that it is wise to calibrate or know where your
> skillet/stove reaches a certain temperature. What temperature is good
> for reflow soldering? How do I measure this temperature?
> 
> * How long should the PCB be on the skillet/frying pan during the
> reflow soldering process?
> 
> I know these are a lot of questions, but I am very interested in this
> cost-effective do-it-yourself technique to solder surface mount and
> fine pitch components on PCBs with ease.
> 

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