I can do the optics but the cost of a microscope doesn’t justify making one in my case. The reflow oven? That’s a ‘project’. 
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I’ve never successfully soldered those leadless parts TQFP are easy.
Next time I try the leadless parts, I’ll make the pads longer so they stick out from the chip a mm or so. I was trying a MEMS chip and you could see where the contacts were from the side of the chip, but I never got it to work. Oh, I think you don’t want to put anything under the chip so the chip is sitting directly on the solder pads.
Anyhow, these counterfeit NRF modules are so easy to come by, easy to use and work very nicely that I tend to use them instead of wires.
Oh. For soldering smd parts, I use a frypan. Electric skillet, actually. I took the thermostat apart and added a wire because the thermostat does not let it get quite hot enough.
So, looking through my magnifier, I use a toothpick to put a tiny dab of solder paste on each pad. It takes a little practice but there’s a big difference between not enough and too much, so it’s not hard to do. You’ll get your first board working. Then I stick the smd parts in place. Forget 0402 parts, they are pernicious. 0603 are manageable. Then, with the parts I want to put on all in their places, I set it on the cold frypan and plug it in. Watch carefully. In a couple minutes, you’ll see the dark gray solder paste turn bright silver, then slurp itself up into the pins. Just unplug the frypan and let it cool. Any bridges are easy to deal with using solder wick and your iron. For an unsoldered pin, I put the tiniest bit of solder on my freshly wiped tip, and apply it to the joint.
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There are several pages on the 'net where this technique is described in more detail, with color photos, etc. I have been doing it successfully for almost two years, using a garden variety, bog-standard, stock, unmodified electric skillet from a second-hand shop. For more details, search this Forum for posts I made, that contain the word “skillet”.
My process is a little different. I preheat the board and skillet to around 150F - 175F (70C - 80C) and allow a minute or two for temperature to equalize. Then I start the actual soldering run.
A good lighted, desktop magnifier is essential. For me, the $20 magnifier lamps from the discount store are more frustration than help. The one I use cost about US$100, but it holds focus well across the whole visual field, and doesn’t have colored fringes around objects.
A binocular microscope, though not essential, is DEFINITELY a BIG help. About US$200 from Amscope.
I’d say that’s an understatement. Considering this approach in light of my life expectancy, I switched over to stencils and have no regrets.
Solder bridges, and loose solder balls jammed between pins, pretty much vanished when I started using stencils and calibrated my wrist to spread the solder paste thin, and evenly. I occasionally get a totally dry joint, but the really insidious ones are where the component appears to have floated on top of the solder and flux, without sinking down and wetting the contact with solder. I’ve heard this is a characteristic of old, expired, solder paste.
With SMD, I discovered that a good joint takes a lot less solder paste than you expect.
Yeah, I use 0805 and 1206 passives. 0603 is usable. For IC’s and active devices, I can (efficiently) work with basic pitches down to about 25 mils (0.65mm).
Dale
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Once, I had just moved and couldn’t find my soldering skillet. So I walked up to the local second-hand junk shop, figuring he’d have one for a dollar or two. He didn’t, but he DID have a 3d printer?!? I still use it.
Yea, I should probably start ordering stencils for my boards. When I started using SMD, the stencil was and extra 200 bucks.
I have noticed a few of the quick-turn board fabricators now offer inexpensive plastic stencils also. There are some stand-alone stencil cutters, such as OSH Stencils and Pololu . Could be time to resurrect and update the thread at Cheap stencils? Where to get?.
Dale
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I used to spend hours squeezing solderpaste though a syringe because a the extra cost of a stencil added too much to the cost for a small board run. However, the cost of stencils has come down dramatically. Last stencil I ordered from JLCPCB was about $6 I think. This is for a laser cut stainless steel stencil. Hardly worth worrying about at those sort of prices and it makes doing small pitched stuff so much easier. You pay more for a frame and electro polishing but for small runs this isn’t essential. I expect other Chinese fabs have similar offers. (No affiliation)
I’ve seen people using some sort of laser cutter akin to a printer to make them. I forget what these things are meant specifically to do so I can’t look one up as an example. Some kind of thing meant for crafts if I remember right so not terrible expensive.
Silhouette or Cameo type craft cutters are what you are thinking of, I think. I did borrow one of these and didn’t have much luck as the driver software was closed source but I think others have been more successful. I doubt if the stencils will be as good as laser cut steel. The demo cuts in Mylar that I tried suffered from ‘hanging chads’. (And you know, these can be a real problem …). I have used laser cut Mylar too but the steel stencils are rather better. Obviously, if you need the rapid turn around this might be worthwhile.
Wow. I’ve got several QFP chips and a tube of solder paste that I’ve had for more than six years, all untouched. I wonder if ‘partial’ stencils are available. I would only need stencils for specific IC’s
Well, forget using all your might to try to squeeze the paste out of the tiny needle. Instead, unscrew the needle from the syringe and squeeze a dab out onto something that doesn’t matter. Then you can easily pick up little bits of it with a tooth pick.
I’m ordering a stencil next time I order boards, and I think I’m going to quit home etching altogether. I already order out anything non-trivial. I’ll start ordering out the trivial things too.
(I used to tell programmers, "Use SQL for all things non-trivial, and most things trivial.)
Over time, the paste gets thicker - and MUCH more difficult to squeeze! (That’s different from my wife, who has also gotten thicker over time but is still quite squeezable.) I suspect the change in the solder paste is mainly due to evaporation of the solvents in the flux. This change in consistency affects not only the squeeze-ability, but also how well the solder paste “prints” through stencil openings, and how well the solder paste sticks to bare copper once you get it into place. When you manually populate a board, and visually observe the soldering process, you have a greater ability to compensate for these effects than if you were using the solder paste in a fully-automated soldering line.
Manufacturers of solder paste specify a shelf-life for their products, typically ranging from 30 days to 6 months, and usually based on refrigerating the material to 40F (5C) or so. I have no idea how much of the shelf-life rating is based on solvent evaporation, and how much is due to chemical degradation of the active ingredients in the flux.
I have resurrected some very thick solder paste, kept in my desk drawer for over 18 months, by squirting some LIQUID FLUX into the paste and mixing until the consistency “seemed about right”. There are a few discussions about this on the web (e.g., HERE and HERE) with no clear consensus about the best procedure.
My “revived” solder paste, using the electric skillet as a reflow oven, seems to flow, wet, and adhere as well as it ever did. It looks like I can get another hundred boards or more from the 150 gram jar of solder paste I bought over two years ago. The same technique should work with solder paste in a syringe, though you must figure out how to get it out of the syringe. Your results will undoubtedly vary.
Dale
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You know, getting the damn stuff from the pot into the syringe in the first place is generally the hardest bit…
Actually fresh solderpaste in a 1ml dental syringe and a 21 or 23G luer lock needle is not too hard to deliver by hand and quite controllable.
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I think the consistency of the solder paste is more important when using the syringe than using the stencil. With the syringe, my limit for efficiently achieving reliable results was about 50 mil (1.2mm) pitch - SOP IC’s, 0805 passives, etc. SOT-23 packages with more than 3 leads were challenging. At those component sizes I could populate and solder boards with very few defects on some days . . . . but spent a lot of time with the solder wick, removing shorts and bridges, on other days. After switching to stencils and acquiring a “feel” for how to use them, those same boards come out defect-free more often than not. (Three-lead SOT-23 transistors are still a challenge!)
Dale
I’ve always bought it in the syringe. I USED to try to use the needle to put it on the pads.
If you dispense it with a 1ml syringe, the pressure you can develop in the syringe is much higher (pressure = force/area) so it is much more controllable. Trying to squeeze it from a 10ml syringe is very difficult and not easy to control. However, I might try using the larger syringe to fill the 1ml one. However, as I said earlier, stencils are now so cheap that unless it is for a one off without too many components that’s the way I would choose.
Yeah, that is an obvious point when you stop to think about it, but also a trivial detail that hides in plain sight. I got out the old paste syringe and - like you said - it’s size is 10 mL . I guess I need to get a package of 1 mL syringes and keep them on hand for small, one-off, projects and rework.
Dale
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We now know Dale’s wife does not have access to his computer…
I have been using laser cut frameless stainless stencils for all my recent boards, inspiration came from this http://www.hoektronics.com/2012/10/27/super-simple-smt-stencil8/ the two most important items are the “Precision Tooling Fixture Block” and the reflow oven. The oven performs better with some modification, start here if you are so inclined https://github.com/UnifiedEngineering/T-962-improvements/wiki and here http://www.electricstuff.co.uk/reflowoven.html with emphasis on removing the masking tape. I found credit cards make particularly good ‘squeegees’.
Two things I have learned,
Stencils come in different thickness’s if you are doing a lot of very fine pads thinner is better.
I order my boards with HASL finish, a couple of times a minuscule lump has been left on the solder surface causing the stencil to not seat flush to the board and allowing surplus paste to leak through. I now ‘scrape’ the the board prior to fitting the stencil, you will feel any lump.
Three things…
I have a lot of difficulty getting low temperature paste to work effectively, I was using it on the second side of double sided boards. Now I use the higher temperature paste on both sides by not putting any large components on the first side reducing the risk of departure from the board when it is heated after being flipped.
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I think this is one of the reasons for ENIG pad finishes. If your source doesn’t charge extra over HASL you might want to consider that finish. (Yes, I know, soldering onto gold finishes feels wrong to us old-heads. But apparently the gold finish on ENIG is thin enough to mitigate many of the issues with gold embrittlement. (Though a top hit scan of a google search does show a wide range of opinion on this…)
I didn’t mention this but my modules have the counterfeit chip. Because of that I couldn’t take advantage of most of the features. I could only transmit one byte at a time and I think I should been able to transmit as many as 32 bytes at a time.
Sparkfun sells the IC. Now I realize all I need is a hot air gun and maybe a stencil. Thanks for the footprint!