Reflow soldering for dummies

Den fredag den 27. maj 2016 kl. 22.20.22 UTC+2 skrev mkr5000:

the solder paste is put on with a stencil, so you control where the solder goes in your CAD

-Lasse

And if you have a decent CAD program with decent libraries, stencil generation is automatic and correct.

You will, of course, want to double-check the gerbers.

Once you find out how much it'll cost, consider that a toaster or a skillet from Goodwill costs $5 to $10, and will do a great job.

and depending on the stencil thickness maybe reduce the openings, common default is same size as pad which in my experience is a bit too much

-Lasse

Yes, I was in that camp until 2007.

Many PCB fabricators now offer stencil services as part of the deal (for additional cost). One thing to know is that you want to reduce the size of the stencil apertures to, maybe, 60% of the pad area. As components get smaller, the apertures need to get even smaller than that, to avoid bridging.

Anyway, if you have a stencil, wiping solder paste on the board and reflowing in a toaster oven or fry pan is surprisingly easy. In fact, it is so simple and works so well, it is quite close to MAGIC!

I bought a P&P machine in 2007 and hacked a thermocouple ramp & soak temperature programmer into it, and it works like a charm. I've done about a thousand boards this way.

If there is no solder paste on the through hole pads, they will stay perfectly clear, for your later manual installation of those parts. I do this all the time, I have through-hole connectors on everything I make.

For one board, I do dip soldering of the many through-hole connectors, there are too many for manual soldering. I slather liquid flux on the bottom of the board, drop all the components into place and then dip into a large solder pot to solder all the parts at once. This process is just a bit tricky, but this board has over 40 through-hole parts, so it is worth it.

Jon

Inneresting. I've only bought one mask -- I usually do prototypes, for which I just apply a dot of solder to each pad, then rosin with a pin. This works well for everything except the various styles that have just a pad on the bottom of the part -- those parts need either more precision in getting the dots right than I can attain, or they need something more forgiving (like paste).

Come to think of it, I could put on BIG dots and file them flat -- I think I'll stick with solder paste, though.

Ok great -- as I thought. So if I send it out I'll just note the SMD pads for flux -- actually, will have to check my PCB program (Sprint layout) if it even does that, I know it has copper, silk screen and solder mask layers.

Do they generate where to put the flux from those? How would I designate -- ok no flux on the pt holes?

Do you use the silk screen layer and edit it? But isn't that for printed text etc?

When I get the CAD figured out I do want to do the oven thing.

periment with SMD and reflow soldering.

of those DIY techniques I've seen posted but also may send the board out to be populated.

pin header, transformer, terminal blocks etc).

I do all the through hole when I get them back) -- will I be able to do th e through hole?

low for larger diameters etc?

for flux -- actually, will have to check my PCB program (Sprint layout) if it even does that, I know it has copper, silk screen and solder mask layer s.

-- ok no flux on the pt holes?

text etc?

there should be a layer for paste

-Lasse

And if there isn't, use a better program!

ok -- haven't updated this program in many years -- maybe there's a paste layer now.

I put a little bit of solder on those pads and take away most of it with solder wick, then I solder them with a hot air gun and put some pressure on them with tweezers. This usually works for parts with legs.

That works great for parts with legs -- you usually don't even need the "take away" step if you apply it right.

But more and more of the parts coming across my desk just have pads on the bottom (I can NOT remember the package names off the top of my head! ), and it doesn't work very reliably at all for those.

If they do the SMD with stencilled paste and reflow the holes will be left untouched. if the do it glued-on parts and with wave solder they'll be plugged.

The solder paste is a mix of solder powder and flux, so both are a single layer.

See:

for Dave Jones' video using a toaster oven. You can watch his failures as well as his successes.

Sorry. You might want to start with this one:

This is so cheap it make no sense working on an oven with a timer:

I think I need to try this in my home lab :-)

Cheers

Klaus

I meant exactly those parts with a (thermal) pad on the bottom. I would not do this for series production but for prototyping or replacing a blown part it works quite well for me. Like recently replacing that step-up LED driver that committed suicide by generating an output voltage way above its maximum ratings. It just better not to forget to connect the voltage feed back pin :-(

What I have problems with are the DFN types. They usually also have a big pad at the bottom and no legs, only metal that ends flush with the plastic case.

And you are correct that for normal parts with legs and no bottom pad (like so-NN) the "take away" step is not needed. It was only meant for the bottom pad to prevent or remove any bumps of solder.

DFN, that's what I was trying to remember -- and those are the ones where you just need to use paste.