I need to assemble about a dozen small boards with one SOIC and a hand full of thru-hole parts on each board. I’ve done them by hand in the past but it’s a pain.
I want to try out the hotplate approach and was thinking that to eliminate hot spots, I would just lay a chunk of aluminum in the hotplate and put the board on it for even heat distribution.
I’ve read that others have applied a thin solder coat to the pads and then set the part down on it before heating. I’ve used a thin piece of masking tape to hold the part down when manually soldering and wonder if that will work in the hot plate? Is there a better way to hold it down?
Do I really need flux or paste? What’s the difference or are they the same? I ordered a syringe of flux and one of paste from ChipQuik to try out but don’t know what I’m doing
Since I only have 1 SOIC, a stencil doesn’t seem worth it.
Can I use flux or paste without a stencil or will I just end up with a glob of solder?
If you just have a dozen boards with one SOIC on them, do it by hand. It will end up being way faster and you won’t overheat your boards.
If you are looking for something new to learn, by all means reflow it – but it won’t be any faster. A couple years ago I made a reflow oven out of a Oster toaster oven. I stripped all of the electronics and replaced them with a solid state relay. The PIC turns the elements on and off. I also did some mechanical modifications to the sheet metal to make it easier to mount a thermocouple in the oven. With that setup I can can reflow an oven worth of board in well less than 5 minutes. However I spend 5 minutes printing the solder paste with the stencil and 10 minutes cleaning up the stencil. I used to use it when doing production runs of 10 to 100 boards.
You will need solder paste. It will have flux as part of it. Kester makes an “Easy 256” paste that seems to be very forgiving of how it is reflowed. It is a no-clean paste that, as the name implies, doesn’t require you to clean it off when done. If you use something with water soluable flux you will need to clean it very carefully immediately after soldering it. As the water soluable flux dries it becomes conductive. It’s very hard to remove after a few days.
When I was getting started with reflowing I found some solder paste at Radio Shack. It came in a little syringe and was about 10. I found that it worked okay, but was a far cry from real solder paste designed for SMT. In my initial experiments I used a hot air gun for melting it. The trick is dispensing a small enough quantity.
denny:
Do I really need flux or paste? What’s the difference or are they the same?
Solder is the actual metal that you melt onto the board. Flux is a goo that helps the solder make a clean bond — it sort of lifts off the impurities and oxides from the surface, to allow the metals to make a good contact. Normally, when you buy wire-type solder, it’s actually a hollow tube with a flux core. You can also buy just plain flux, which sometimes comes in handy. But you can’t make an actual connection with only flux, you still need some solder somewhere.
Solder paste is tiny granules of solder suspended in flux.
kb0thn:
In my initial experiments I used a hot air gun for melting it. The trick is dispensing a small enough quantity.
I’ve had some success putting a blob of solder paste on a plate and then applying it to the circuit board with the tip of a needle or a piece of fine (30ga) wire. It’s a PITA but it works.
If you’re using parts that allow it (e.g. not QFNs), I recommend the “glob a lot of solder on and then remove the extra with solder-wick” technique.
