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Possibly many questions have been asked on soldering smd parts, but I haven't found specific answers, Like:

  1. Do you use a watchmakers lens or some other type of magnifying glass while soldering these miniature components? What would be most optimum to see a larger picture?

  2. How do you solder components where pads lie beneath the package, I don't own a reflow oven and have tried to ignore these packages but can't do that anymore. Are there any techniques to manually solder BGA, iLCC, CSP amongst others.

  3. What tools do you use, apart from tweezers, soldering iron, solder wire, and a bright/ illuminated workplace. Any suitable "third hand" that you have found that makes a monster of a difference?

  4. Is there a specific tip thickness to use for the soldering iron, what about the solder wire guage?

  5. For prototyping if would not always be feasible to make a pcb, do you solder these components on a veroboard or do you buy a breakout board?

You could add more to these based on your experience and wisdom...

Your turn.

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8 Answers

up vote 23 down vote accepted
+50

Before I start, this is a lot of questions in one question. Please try to break it up a little more next time.

One: Do you use a watchmakers lens or some other type of magnifying glass while soldering these miniature components? What would be most optimum to see a larger picture?

This question discussed optics in further detail. I have a 10x loupe that I use to inspect solder joints when I'm not at the microscope workstation at school or work, but there is no doubt that the stereo microscope is the best tool. Stereo gives you depth perception.
As far as seeing the larger picture, zooming out (microscopes I've used go from ~3x to 40x) gives you plenty of room to find your place if you're concerned about that. Zooming in, however, is when a scope shines. You will burn tall plastic parts (like connector shrouds) for a while, but eventually you get a feel for where your iron is outside of the field of view. A good microscope will give you about a 3" focal length (contrast with a cheap loupe, mine is probably about 1.5" for 1/4 the magnification), so you can wave your soldering iron halfway between the two until you see a fuzzy brown cloud moving through your field of view. Move the iron back until you see the tip, and only then lower it to the pad you're soldering. A lighted diopter lens doesn't provide enough magnification, in my opinion, to justify the obtrusiveness of having the lens in the way. Same with the magnifiers on helping hands.

Two: How do you solder components where pads lie beneath the package, I don't own a reflow oven and have tried to ignore these packages but can't do that anymore. Are there any techniques to manually solder BGA, iLCC, CSP amongst others.

If at all possible, stay away from BGA type packages for hand soldering. In a pinch, iLCC (and the more common QFN) packages can be done by placing small domes of solder on the pad (which must extend outside of the chip boundaries), fluxing the bottom of the component, and heating the solder. If all goes well, the solder will melt, heat the contact on the chip, and the surface tension will pull the joint together. For low pin count devices, this works quite well, including crystal oscillators. If the contacts extend up the side of the chip, just heat those. Another option is hot air guns or hot air soldering stations. Steinel makes good air guns, and many soldering stations have air attachments. I've found that air guns are more effective than solder stations for applying/reflowing chips, they just seem to apply the heat more evenly and sustainably. Pay attention to the reflow profiles: You want to start heating it up slowly, over a period of a minute or two, and only then actually apply the real heat. Thermal stress is a real concern here. Note that I've only ever used this method for rework; I haven't tried it for assembly runs.

Three: What tools do you use, apart from tweezers, soldering iron, solder wire, and a bright/ illuminated workplace. Any suitable "third hand" that you have found that makes a monster of a difference?

Solder wick. Miles and miles of the stuff. For most work, even fine pitches, normal .11" stuff is fine, but the smaller stuff (.05" or .03") is helpful. Most tutorials will have you apply it rather indiscriminately. For fine work, you want to lay it parallel to the edge of the chip, poke the edge nearest the pad with the tip of your soldering iron, and slide it over the PCB until it contacts the edge of the chip. Be wary of allowing little shreds to break off and cause shorts.
For helping hands, I've used a Panavise 301 with the 312 tray base. It holds the work 10" off the table, which lets you steady your elbows. However, some people like to put the work on the table (on an antistatic pad, of course), so you can steady the heel of your hand instead.
Last, and probably most importantly, you'll want flux. Flux pens are cheap and easy to find, but I have a little dropper bottle that I like better - You don't have to worry about damaging anything if you drip the flux onto the PCB. This, of course, mandates keeping some isopropyl alcohol and cotton blotters on hand to remove the residue intermittently. Oh, and you'll also want a spool of 30-gauge wire-wrap wire to fix mistakes.

Four: Is there a specific tip thickness to use for the soldering iron, what about the solder wire guage?

This depends completely on what you're doing. I have a 1/32" cone that I use for most everything, and I use standard .031" solder for connectors, through-hole, and wiring work, and .01" Kester 44 for fine work. You'll just have to experiment.

Five: For prototyping if would not always be feasible to make a pcb, do you solder these components on a veroboard or do you buy a breakout board?

I usually dead-bug tiny components: Superglue the top, attach to protoboard (like Twin Industries 8200-45-LF), and then run 30-gauge wire to each of the pads, like this, and connect to headers or whatever you need to do. (Note: Pic of someone else's work, not mine). Then, after verifying that everything's in the right places, put a blob of hot glue over the whole thing to give the wires some strain relief.

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humble +1, Speechless!! –  Kevin Boyd Oct 1 '10 at 19:28
    
For BGAs, when you can't avoid them at all, there's schmartboard: schmartboard.com/index.asp?page=products_bga –  fceconel Jan 13 '11 at 16:16
    
Re: BGAs - I etch a stencil and reflow on a hot plate. You can probably get a local arts store to laser cut mylar for the stencil, and buy a toaster oven for the reflow if you can't find a hot plate. –  krapht Jan 14 '11 at 20:09
    
OK, so it is possible to do BGAs. However, you can't inspect them without X-Ray equipment. I figured that anyone who has the equipment and know-how to do BGAs would be unlikely to read this post, and those who were reading this post would be unlikely to have that equipment and know-how. Turns out I was wrong twice. –  Kevin Vermeer Jan 14 '11 at 20:41
    
@ fceconel: Have you used schmartboard? what are you reviews of it? –  Kevin Boyd Jan 16 '11 at 6:35
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I use:

  • Stereo microscope (with a focal-distance increasing add-on lens) and fiber-optic microscope illuminator.
  • Hot-air soldering station (cheap chinese crap, significantly modified).
  • Good-quality soldering iron. (I have an OKI-Metcal RF Heated soldering station).
  • A syringe of solder paste

  • and most importantly good tweezers

I'd say the most important things to success are a good pair of tweezers, and solder paste. You do not need a solder-stencil. A simple syringe with a fine dispensing tip gives you much better control over solder volume than using wire solder. I can even get away without using solder-wik most of the time.

BGA packages and other package types with lots of leads on the underside of the device are pretty much our of reach of simple hand assembly, since checking your soldering job requires a x-ray inspection station. Also, mask registration becomes progressively more important as the parts get smaller, and hand-dispensing the solderpaste is no longer effective. It may be possible to manage with a solder stenciling jig and a reflow oven, but I don't have much experience there, and fixing a botched solder job is likely to be very difficult.

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+1 Nice! What make microscope do you use? Have you found it very useful vis a vis a single eye piece. Never heard of RF heated soldering stations before, will try to do some webbing for these. –  Kevin Boyd Oct 1 '10 at 11:39
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Metcal, and now Oki-Metcal soldering irons heat the soldering iron tip inductively using rf. Basically the iron has a ceramic covered wire coil in the handle, and it induces eddy currents in the actual tip which resistively heat it. It has a very large instantaneous heat capacity, which means that you can solder large components using a small tip, and your dwell-time on each component lead can be less, which reduces the chance of damaging something. –  Connor Wolf Oct 2 '10 at 2:10
    
As for the microscope, I never use it monocularly. Having depth perception is tremendously useful. Brand-wise, it's a cheapo chinese thing. –  Connor Wolf Oct 2 '10 at 2:11
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I use a Veho USB microscope (about £40 on eBay) or a x15 loupe.

I sometimes use a tiny spot of blu-tack to hold a component in place. Flux is essential, as is solder wick for cleaning up errors.

I tend to etch my own breakout boards, they are shockingly expensive to buy.

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+1, Good thoughts! What about soldering BGA etc. ever tried those? Nice idea about the blu-tack. What solder station do you prefer? –  Kevin Boyd Oct 1 '10 at 11:44
    
My iron at home is junk. I do like the Metcal at work though. BGAs are impossible for hobbyists as far as I can tell. –  Toby Jaffey Oct 1 '10 at 12:39
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I personally use an old Pace station. Temp control helps tremendously. –  Jesse Oct 2 '10 at 16:28
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If building in any quantity, we use a pick and place machine. Or have your CM (Contract Manufacturer) use one. There are even CM's that do short runs.

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Indeed. I was going to answer this with "a credit card". –  Jeanne Pindar Jan 14 '11 at 2:22
    
Why the down votes? Not everyone here is a hobbyist, just building one and a good solder. –  Brian Carlton Feb 2 '11 at 4:29
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I use one of these SM-20 stereo dissecting microscopes.

For soldering I use a Metcal system. They are expensive if bought new, but an old STSS power unit can often be picked up cheap on Ebay, and used with the later MX-500 handpieces and cartridges. I think it can also be used with the latest MX-5000 accessories, as well, but I haven't tried them.

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upvote!, Haven't used any of the Metcal's before, what are the pros of these over other soldering irons or stations? –  Kevin Boyd Oct 1 '10 at 14:24
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Very rapid heating when switched on, excellent temperature control, large range range of cartridges, and massive heat capacity. –  Leon Heller Oct 1 '10 at 19:49
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You might find this tutorial interesting, by Jon Oxer from Freetronics.

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+very informative! –  Kevin Boyd Oct 1 '10 at 14:21
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Tools

Hakko 936's are cheap (at work it was ~$85 from a supplier) but perform great. They don't heat up as fast as some of the newer irons (ones where the "tip" includes the heating element), but in easily under a minute. The standard tip that they come with I've used for soldering everything down to 0.50 mm QFNs. They even make knockoffs of them if you're trying to save a buck.

And yes, tweezers. Get a few different styles and if they get bent much, throw them away.

Materials

For moderately fine-pitch work, 0.015" is common, but have some 0.025 or 0.031 for thru-hole so you're not using an inch of solder per connection.

I've found using tacky flux instead of flux pens works quite well. I got a 30 g tube of some Kester tacky no-clean RMA flux (forgot number) from my rep for free (out of expiration date) when I bought some flux cleaner and it's proven to perform much better, if being slightly less convenient. A fine-point Luer-lock tip and I can put a dot right where I want. It also can hold fine parts down fairly well and sort of dampen some hand vibration when nudging parts.

30 AWG Kynar (wire-wrap) wire is great when that connection somehow slips through your layout package's DRC or you FUBAR the pinout and have to rotate the part and have half of it hanging up in the air

Techniques

As far as techniques for some leadless/bottom pad parts, I usually go with reemrevnivek's dead-bug approach if I can't get the same part in a more convenient leaded package.

If you want to put them down onto a board, bottom pads can occasionally be hand-soldered with a sufficiently large via under the pad, even large-pitch BGAs (have not personally done BGAs). Alternatively, you could attach the leadless components with solder paste and hot-plate reflow before hand-working the leaded components.

I work around the third-hand problem for SMT placement by putting a minimal amount of solder onto one pad (be it for a TQFP-64 or 2512) then tacking the part down. For ICs, you might have to nudge it just-so to align it properly, then tack down an opposite corner then go to work. Be sure to hit the tacked locations again to get a proper joint.

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+1, Good thoughts for soldering leadless components! –  Kevin Boyd Oct 3 '10 at 6:40
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The most essential tool for me is a headband magnifier: alt text

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Thanks for the pic, what brand is it, what is your feedback regarding this device? –  Kevin Boyd Jan 17 '11 at 16:50
    
@Kevin Boyd, it is from modelcraftcollection.com. The magnifier is very convenient, allowing you to see the components from any angle (unlike a helping hand magnifier whose position is fixed.) The lamp is less important as you generally have a desk lamp pointed ad the object anyway. –  finnw Jan 21 '11 at 17:33
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