TOOLS: Soldering supplies

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This week’s tool is a collection of stuff: the things we use for soldering. We regularly work with surface mount (SMD) parts down to 0603, but it doesn’t take expensive or exotic tools:

  • Solder. We use 60/40 tin/lead solder, it is the only way to go for hand prototyping. It makes recycling parts with hot-air much easier than lead-free solders, which is probably a net positive for the environment. Most solder has some flux, ours lists 2%, but it is never enough, use more! We had been using a 0.7mm wide solder, but recently found a 0.5mm reel. The 0.5mm solder is thin enough to solder SSOP and QFP pins individually, which means there’s less excess solder that needs to be mopped up with wick.
  • Flux. Flux helps solder flow better, and keeps it out of places you don’t want it. Don’t even try to solder without copious amounts of this magic goo. Our syringe of flux came from a surplus store. According to the label it expired in 1991, but it still works great!
  • Solder wick. There are almost always solder bridges between the tiny pins on hand-soldered SMD chips. Apply a little extra flux to the pins and mop up the excess solder with wick. Wick is the trick to soldering SMD without attending to each pin individually – glob down a bunch of solder and soak up the excess with wick, enough remains behind to connect the part to the PCB.
  • A sponge. An iron covered with soldering gunk doesn’t conduct heat well. A clean iron is much easier and faster to work with. We use a giant natural fiber sponge moistened with a bit of water to clean the iron. We give it a quick swipe whenever the iron looks dirty. Go for a big one, the tiny sponge in the iron holder is totally insufficient.
  • Tweezers. We use ’00’ size surgical tweezers to hold SMD parts while soldering. The pointier the better. These were 50 cents at a surplus store.
  • Jewelers loupe. A loupe magnifier is a must for inspecting SMD connections. It doesn’t need to be expensive. We won this loupe in Hacked Gadget’s Halloween contest a few years ago.
  • Sticky tack/poster tack/Blu-Tack. This is a sticky putty often used to hang posters in student dorms. We use it like many people use a helping hand. It can hold a board steady and keep parts in place. We also put it on the end of a pencil for a simple vacuum-lifter alternative. Also used heavily in the photo studio.
  • A bright desk lamp. The importance of a bright light cannot be understated, especially for surface mount soldering. The smaller it is, the harder is is to see in the dark.
  • Soldering stations and Storage are within reach.

Board stuffing is an art. Nobody does it the same. What’s in your prototype building arsenal?

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7 Comments

  1. I think lead vs lead free is overblown. Lead free isn’t that much if any harder to use IMHO. I only use lead free at this point. Joints can look worse but it doesn’t mean they are worse depending on the solder type.

  2. excellent collection, ian. i’ve never thought of using poster tack before.

    dental pick:
    useful for debugging boards if you suspect a cold solder joint or a pin that’s not connected. gently prod the suspect pin and see if it moves around on the pad. if it moves, reflow/add solder, etc.

    stereo microscope:
    i got mine dumpster diving when a previous employer was throwing out some old equipment. it’s great for really seeing what you’re doing (i regularly solder down to 0402). they can also be had on ebay for around $100 (from what i hear).

    helping hands:
    not sure if this is previously covered or not. get a couple of cheap sets from jameco or the nearest surplus store for a few bucks a pop. they also come in handy when doing soldered cable assemblies (one for the connector and one for the conductor being soldered).

    flux pen:
    liquid flux put into a pen with a small wick on it. how it compares to the other stuff is probably just a matter of preference. gotta use flux for the SMT stuff!

    soldering tip:

    one of the tips i’ve found very useful is using two irons for SMT passives. go around and quickly dab a bit of solder to each pad. then use the tweezers to roughly locate the component. after your components are in the right general place, go through and move them around with an iron on each end, basically dragging them onto the proper location on the land.

    make sure you contact both the solder pad and component simultaneously to ensure a good joint.

    this winds up being much faster with smaller components, since you’re not trying to hold them down with something like tweezers or a dental pick. you also don’t have to worry about tombstoning as much as when soldering one lead at a time.

    1. –helping hands – I have never had luck with these. Maybe mine were cheaply made, but I could never find a situation where it helped more than it hurt :) That is when I went with the sticky tack. It holds wire to connectors, pin headers and SMD parts in place (when turned over for soldering), even hold a SOIC while you solder the first pin.

      –flux pen – Any recommendations? I’m looking for an alternative to the surplus flux (no longer available), I’ve tried a few and disliked all of them.

      –Two irons is interesting, sort of like a hot tweezer approach. I will have to try it. I have lots of problems with tombstoning and usually hold things with tweezers to prevent it.

      My current approach is to put solder on one pad of every footprint on the PCB (remembering to use the pad closest to my solder hand). Then I hold the part in place with tweezers and heat the solder until it reflows into the part. At the end I rotate the PCB (unsoldered pads closest to iron hand) and solder all the remaining pads.

      Thinking about your idea makes me really want some hot tweezers :)

      1. – helping hands. i probably use them more for soldered cable assemblies than i do for boards. it helps if you put a small (2.5 lb) weight on the back of them if they need to hold anything with any amount of weight. i really like the idea of the poster putty for holding boards. at work i normally use a panavise with a circuit board holder – those work pretty well in most cases.

        – flux pen. i’ve been using a kester 951 pen for years (it’s also expired now but still working just fine).
        http://www.mouser.com/ProductDetail/Kester/83-1000-0951/?qs=1rIBfDHV7idrQGoioMlPog%3d%3d

        just beware that it’ll take forever to ship because it needs to go ground due to the chemicals.

        the main tip i can offer here is to get enough on the board. the tips are spring loaded and actually depress if you push on them a bit. this will really get the flux flowing. i normally only need to push on it when i haven’t used it for a while, after that a simple dab works just fine.

        -two irons: i was very hesitant to try it at first, but it didn’t take much time to get use to. i use some really simple weller WLC100 soldering stations at home that work just fine (with a fine conical tip). i can’t stress enough how much faster (and reliable) this is after you get accustomed to it.

        i’ve never used hot tweezers before. it seems like they’d be better for desoldering, where you don’t really care about making contact with both sets of material at the same time. . .i’d be curious to hear from someone that’s used them.

        i certainly can’t take credit for the dual iron approach. i simply adopted it after hearing about it from multiple employees of Murata (the capacitor company).

  3. The things they have at work that I miss on my home bench are: 1) enough space, 2) Metcal soldering iron with many assorted tips, 3) binocular microscope. I guess a surplus microscope might be affordable, and I could pretend it would double as an educational tool for the kids…

    I only use two irons for removing parts, but maybe I should try two when installing. It seems tricky, though.

  4. tweezers were a topic in the forum, i have been using a pair with rounded padding. allowing me to twist the tweezers and rotate parts with excelent dexterity.

    i have been missing the stereo microscope, ill be looking for another probably smaller unit soon.

    having multiple irons is a good idea, i have a 30 watt Weller that is older than me, that i use for larger parts, and a fine tip temperature controlled one.

    i use tip tinner/cleaner after sponging the tips, they tend to last longer and do a better job than without.

    an x-acto knife is a must have, from opening small parts bags to cutting traces on PCBs, i use it just as much as my irons.

  5. I do most of my SMD soldering with water-soluble flux. Its extremely aggressive but washes clean under warm or hot running water.

    I use Kester 63/37 leaded solder with 331 flux. I also have a little applicator bottle with Kester AZ2331 liquid flux that I apply to the board and component leads before soldering.

    The nice thing about this flux is that its so aggressive that drag soldering works really well. But be sure to wash the flux off within a couple of hours after applying it – extremely aggressive equals corrosive. It WILL pit the metal and make it look dull if you leave it on too long. Its also very conductive and will mess up sensitive analog circuits.

    That said: it washes off very easily and turns to what looks like soap bubbles when water hits it. Just rinse the board under a spray nozzle (kitchen sink) or with a hand-shower until you don’t see any more soap bubbles. Then blow dry with compressed air (if you have it) or using the exhaust port of a vacuum cleaner.

    I’ve checked several times – surface resistivity is in excess of 10^15 Ohms after blowing the water off the board with compressed air.

    I’m old and have old, tired eyes. I do most of my SMD soldering using a surplus Vision Engineering Dynascope that I picked up for several hundred dollars. What’s so cool about the Vision Engineering scopes is that they display the image on a flat screen rather than you forcing you to keep your eyes on microscope occulars. Its much easier on the neck as well. My particular unit does X6 toi X40 magnification and uses a ring light for illumination.

    I also use something that I call my “Black and White” microscope. This is an electronic microfiche reader that has a gorgeous lens assembly feeding a 1/2″ B&W vidicon that then feeds a 13″ B&W monitor. The maximum magnification appears to be similar to the Vision Engineering Dynascope – I’m estimating that its somewhere near X35 to X40 but goes down all the way to about X6 or so.

    I actually find the B&W unit easier to use but the other guys and gals in my shop prefer the Dynascope. Some day, something electronic in the B&W unit will die and then I’ll get around to installing a modern camera and LCD monitor into the chassis. All of the magic is in that marvelous lens assembly – the rest is just ordinary stuff.

    I mention the B&W unit because you can often find similar units being tossed out or sold inexpensively.

    dwayne

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