high density SMT relow

"Jon Slaughter" schreef in bericht news:hd9m4a$je5$ snipped-for-privacy@news.eternal-september.org...

It's the basic idea, yes. There are some other things to be taken into account:

- The correct amount of solder.

- On the correct places.

- The correct temperature traject both up- and down. Still only the most important.

Carcia Circuit Cellar published a design using some kind of toaster oven. Elektor did the same but somewhat later in time. Now Elektor sells reflow ovens, priced some 1200 Euros. (FAIK ex. VAT and shipment)

petrus bitbyter

I've done home reflow with paste and a $20 hotplate. I do 0.5mm pitch quite regularly, 0.5mm QFNs occasionally, and 0603 is HUGE :-) I've done CSPs but my home-brew boards are too flexible for them to stay attached.

I recently added an alumimum plate to the hotplate, so if you go searching, choose an alumimum hotplate instead of cast iron. My process is basically "apply paste, place parts, heat until reflow".

0403 parts are fairly easy to solder by hand if you work under a microscope. Using flux will make life much easier. Any leaded IC is easy to solder by hand down to 0.5mm pitch. Non leaded ones are harder, but can be done by hand if the part leads come out to the edge of the part. If parts need to be soldered to a plane, preheat the board to 150 deg C.

If you want to do BGA or QFN, lay down a thin layer of solder paste on flat glass and dip the BGA into the solder paste. Place the part on the board and bake. I use a waffle iron with reversable plates. I use the flip side has flat plates for doing grilled cheese sandwiches. Works better than a toaster oven. Use no-lead paste for BGAs since the balls are most likely no-lead (don't mix solder chemistries). Another technique I use is tinning each PCB pad, coat the part pads with flux, place and bake. This is very useful for leadless parts like power supply controllers.

You can get hot simple hot air rework equipment for under $400. Made in China, but works well for occasional rework.

Hot air preheat plate. Need to raise the plate by 1/4". Making the plate larger in area is also helpful.

Hot air rework

Soldering iron. The PS-800 might be on its way out, so may need to go to PS-800E or 900E.

Hmc has a poor selection of tips.

Do you paste by hand or have a stencil? Could you list the paste and glue you use? I might do a few tests and see what I get. I'm assuming you don't use any heating profile ;) (I recall that was a big deal for "proper" reflow methods.

Wave would be nice but seems to require a load of expensive equipment. Not sure if it could be done successfully with DIY techniques.

The heating profile is not necessarily hard to do. I've seen several DIY modules for proper heating profiles. I'm not sure though how important it is for DIY though.

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I must admit that if the part is any smaller than an 1/8-watt resistor, I can barely see it to solder it anymore. (Getting old is a bitch!)

I guess that's a bit of an exaggeration, but I swore the last thing I worked on that used small SMD's and hand-soldering (prototype proof-of- concept stuff), would be my last. And so far, it has!

-mpm

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pcb-pool.com will give you a free stencil with your pcbs, and their sister site

will sell you oven, controller etc. needed for reflow for 129=80

-Lasse

I've done both. There's a local guy that laser cuts kapton sheets, or you can just use a syringe.

I don't use glue. For paste, I use whatever's cheapest since I don't bother refridgerating it.

Nope. My hotplate heats to reflow temps in about 5-6 minutes so it all works out, I just manually remove the board once all the paste is melted. The hotplate only heats the PCB, not the parts, so the paste melts before the parts get as hot.

"DJ Delorie" schreef in bericht news: snipped-for-privacy@delorie.com...

That's how you build up some stress in the components and solderjunctions that may give problems over time.

petrus bitbyter

So you get decent accuracy that way? I would imagine that in some cases the leads wouldn't align properly? I guess the surface tension may do the job though...

I might just go look for a small toaster oven and build a simple controller. Shouldn't be difficult. A triac, some temp sensor, and pic should do the trick.

They come with a thermostat. It's a bimetal bang-bang, and I don't know the hysteresis, but mine does pizza just fine. ;-)

Cheers! Rich

There are now nice looking SMD reflow oven on ebay for only a few hundred bucks. Buy one and start experimenting. I think gone are the days of hacking a toaster oven etc.

Dave.

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The only key is to put the right amount of paste down. If you do, it all works. If not, a little hand-cleanup with a fine tip iron is all it takes.

In my initial attempt[s] with the hotplate method, I had a bit of board discoloration. Mounting a clear sheet of polycarbonate above the board (at least on first attempt) seems to help that a lot. DJ, have you had this problem? Do you use anything to make the heating more uniform?

Otherwise the method seems to work pretty well.

I use an aluminum plate (about 8x8x1/4") to equalize the heat. Nothing above it. The only discoloration I've gotten was one time I tried to do a couple boards in a row without letting the plate cool down; the epoxy nearly caught fire. Circuit still worked though.