Reflow soldering for dummies

Yes. We do surface mount on an auto pick-and-place, solder and inspect, and then add the thru-hole parts by hand. Make sure the solder paste stencil doesn't paste the thru hole pads.

They will if you paste them. Don't. The flux should be cleaned up by the assembler so the holes will be clean.

ENIG (gold over nickel) PCB finish is fabulous, beautiful to solder after years of storage. Solder coating can get a bit oxidized by the reflow oven.

It's not hard. People will make laser-cut mylar paste stencils cheap, sometimes free. They won't last as long as stainless but they are fine for small quantity production.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin
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I have a post-it on the door of my office.

NO QFNS

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

I was once wary of 1206's. Then 0805s and 0603s and then BGAs. They all work fine. BGAs are more reliable than leaded parts.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

We delete the thru holes from the solder paste stencil. There is no flux as such, just solder paste that includes flux in the goo.

You should receive the boards with the surface-mount parts soldered and clean. The thruhole pads and drills should be perfectly clean, solder-free and flux-free.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

I love QFNs and DFNs. They're easier if they have the wettable flanks. When asked, I tell the manufacturers I'll use their Q/DFNs if they include the wettable flanks. Evidently I'm not the only one because most are including the detail.

Reply to
krw

Thanks, I've been thinking of a toaster oven for doing some smd parts on boards. Right now we do them "by hand", each one soldered in place under a microscope. But these are when there are only a few smd parts... for more we send them out to a board house.. which means a relatively big buy in terms of numbers... 100's.

I've watched some videos where people put down blobs of solder paste by hand... out of a plunger thing. That looks almost as painful as out "by hand" method.

So can you give me some guesstiamte on the price of a stencil? ~$100? Do you then panelize the boards and do several at once... Do you use SS for the stencil?

George H.

Reply to
George Herold

Tim, do you mean a dot of solder, or a dot of solder paste? (assuming just solder, does the rosin flux then hold the part to the board?)

George H.

Reply to
George Herold

There are lots cheaper stencils than that. For small volume, Kapton is okay, but mylar is garbage because it doesn't laser-cut cleanly and snags easily.

Stainless is better for medium volume, obviously, but don't dent it!

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Phil Hobbs

There are lots cheaper stencils than that. For small volume, Kapton is okay, but mylar is garbage because it doesn't laser-cut cleanly and snags easily.

Stainless is better for medium volume, obviously, but don't dent it!

Cheers

Phil Hobbs ==================================================================

Maybe this could be a niche for one of those cricut.com cutters that came up for cutting thin copper foil, making your own stencils from mylar?

----- Regards, Carl Ijames

Reply to
Carl Ijames

I do prototype/development work. My run is generally fifteen to thirty boards. Our CMs don't have a problem with this quantity but they also charge us for it. It's almost as much work to make 10 as it is 100, so we expect to pay.

That's what our CM charges us for a stainless stencil (one per side). He says they just pass through the cost.

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Reply to
krw

We've had good luck with a hot plate, one of those magnetic stirrers for lab use with the magnet removed

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$17.70 for a 13x21cm aluminium stencil

-Lasse

Reply to
Lasse Langwadt Christensen

There's too many things I need to do for which only QFNs are available. So I've acquiesced.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

For SO or QFP housings I just put a bump of solder on all pads by having a thick drop of solder on the tip and move that fast over all pads. Normally surface tension prevents shorts here. If it still happens it is easy to fix in this stage. Then I place the part on these solder bumps and just fix two corners with the tip. The rest is the done with a hot air gun with a 1-2mm nozzle. During that I put light pressure on the chip with tweezers. Look nearly like soldered in the oven.

I even solder Rs and Cs this. I just do not fix them but heat the pads with hot air and put the part into the molten solder.

--
Reinhardt
Reply to
Reinhardt Behm

Solder, with an iron. Nice shiny (if I'm doing it right) dot of solid medal. Then I use a rosin pen (NOT "pin", dammit!) to apply rosin. The rosin from that pen, once the solvent flashes off, is gummy.

The rosin flux holds the parts weakly to the board -- not as good as the solder paste that I have, but then with the solder paste I have you still want to walk carefully to the reflow skillet if you want everything in place when you get there.

Just using stencils would be better -- I just need to remember that when I order boards, not when I'm starting to build them.

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Tim Wescott 
Control systems, embedded software and circuit design 
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Tim Wescott

I am working on a prototype right now with 0402 and fine pitch microcontrollers

I was stubborn enough to assume that all would go like planed, right now I am soldering on stuff I can barely see :-) (but it looks nice)

Cheers

Klaus

Reply to
Klaus Kragelund

We don't like 0402's, because they tend to tombstone. That's not a problem with hand soldering.

Get a Mantis if you plan to do a lot of soldering or rework of small stuff.

The great thing about BGAs is that you can't see most of the solder joints, so you don't worry about them.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

0402s require a tighter process and the pads are sorta semi-circular but otherwise, they're fine. It's our standard size for Rs and Cs.

Absolutely! Your eyes will thank you, though your wallet won't. The SLWD lens is a big improvement, as well but your wallet will really hate you (my boss didn't flinch - too much ;-).

Reply to
krw

It may be just me, but I do fine with 0402 resistors using a 6X microscope. At least -- if I do the work at the right time of day. Right after I've had some tea my hands shake too much -- too much differential gain, apparently.

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

Most likely stainless steel stencil in an aluminum frame.

The thrift-store toaster-oven method has to be seen to be believed. At least for me. Now it's all I do for at home projects.

Reply to
DemonicTubes

you are right it actually say so on the page; laser cut steel on aluminum frame

Reply to
Lasse Langwadt Christensen

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