Just a little addendum...

If curious, the boards I'm doing are the 3rd, and really hopefully 
final, proto of:
http://www.celestialaudio.com/4ch/index.html
the one pictured was done by hand with a soldering iron, since it was 
before I got going with the toaster oven.

I got my paste from techni-tool.com
kester R276, bought 3 syringes, almost out, lasted a year and did quite 
a few boards with it.  p/n 488SO540
I also got two needles: 272PR021 and 272PR939.  I use the larger one a 
lot, the smaller rarely.
the plunger for the syringe came from digikey: KE1505-ND.

I would recommend getting the larger needle of the above and something 
even bigger to make it easier to put paste down on largeish pads.  But 
not really needed.

J






Jesse Lackey wrote:
> 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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