In general, soldering is just melting metal between like pieces of material. Not all things can be soldered: If you try and solder batteries, you will have a rough time, as solder won’t stick to (most) battery terminals. If you ever look at battery packs, they are actually spot-welded together. For an excellent description of the kind of equipment used to do this, check out the $100 Battery Tab Welder. I have nothing to do personally with that web site, but I think it’s a very good description of how to do basic battery-tab spot welding.

My Past

When I first started soldering (in elementary school), I had my cheap Radio Shack wall socket iron, and just couldn’t do it right. It wasn’t until the “Science Dude”, a retired engineer who lived by my school invited me back to his very well equipped basement lab to teach me how to do it right. I’ll dedicate a whole article at some point to the Science Dude, as he was a man who really loved engineering. My first introduction to lathes, interferometry, soldering, oscilloscopes, injection molding, and basic physics were provided by him. Science Dudes’ true identity was Roger Brandt, and one of his claims to fame was to design a very important little thing that made modern toothpastes containing fluoride possible (US Patent #3,260,410).

His first lesson involved making good solder connections. My first circuit was a timer/counter and a power supply to run it. Eventually I was building amplifiers to sample digital audio into my Atari 800XL (an 8 MHz 6502 with 64K of memory), among other cool projects.

There is really only one really important lesson to remember about solder: You’re working with a liquid, molten metal. Keep this in mind, and several things will become apparent. You can flick it off, it will soak into things, and it forms a meniscus with things when it touches them. What follows is a my guide to solder connections, referring to “you’re working with molten metal” wherever it is pertinent to the discussion.

This is a bid sparse on images at the moment. I’ll take some photos and get them up here to illustrate some key points below.

First: Tinning

Tinning is the term used to describe a thin coating of solder put on component leads before you attach them. Did you ever wonder why professionally made circuit boards have all the holes and pads shiny silver when the copper cladding is actually copper color? It’s because when boards are made, they are passed through a solder bath that tins all the pads and holes. This is necessary to prevent corrosion on the pads as well as to make the boards easy to solder to.

If you buy components and are going to attach them to a board, the leads are most likely already tinned. That’s why leads on most through whole components are actually silver in color, as they are either pre-tinned or otherwise coated to make soldering easier. Tinning, however, is still essential.

The first important part of tinning is keeping your soldering iron tip covered in a thin layer of solder all the time. You’re working with molten metal, and it’s this that actually carries the heat. Always keep your soldering iron tip tinned. When I’m building, I typically wipe, tin, flick, and then solder, where the “flick” is a finally tuned wrist motion that can effectively remove a solder ball from my iron tip without re-wiping.

Most quality irons have silver (or otherwise) coated tips, which really helps with heat conduction and solder contact. In general, a soldering iron tip when touched to solder should immediately look wet with solder in a nice even coating. If you have a big ball on the end, that may be too much for the job at hand, unless you’re doing SMT drag soldering or lots of DIP pins. If you keep a very “dry” tip, first of all you’ll find that each joint takes a very long time, and secondly, your soldering iron tip will carbonize (turn black) more quickly, which may eventually ruin the tip. If your iron tip is black, wipe it and re-tin it with solder, as the char than forms on soldering iron tips is no good for transferring heat to a joint.

If you ever are facing bare copper (such as attaching connectors), you should tin the wire as soon as it is stripped. Strip the wire longer than you need, then twist the conductors together if it’s stranded. The twist helps keep the individual strands from splaying apart when you go to attach it.

After the twist, tin it. You should see the molten solder wicks up into the wire a bit. Sometimes this leaves a little blob at the end of the wire, which I typically remove by just “flicking” the wire with the tip of the iron, and letting the wire spring back, sending little molten solder balls flying off the wire. Then, I cut the wires to length, and I’m ready to attach them to the connector. When flicking, make sure you pay attention to where the solder balls go. You don’t want them in your eyes, or falling into your lovely intricate circuit.

Especially when working with small stranded wire, tinning makes them easier. In general, if I can’t just slide the wire into the hole (as is case with certain through hole wire termination), I will tin the wire first, and then attach it. Just trying to solder bare copper to a connector will often leave you with little solder-covered strands sticking out of your solder connection, posing a short circuit risk.

Second: make a good mechanical joint

When I first started, I assumed this meant wrapping a wire around a pin several times and squeezing it on with pliers. This is not necessary. Making a good mechanical joint is mainly important to keep your wires from popping off and springing around when you are working. In many quality connectors and cables, its not actually the solder joint (or crimp joint) that fails, but the copper wire leading up to the joint. This is why strain relief is important, which I’ll cover in a later article.

A solid mechanical joint could be as simple as a through hole DIP package in a circuit board, or a wire looped once through the terminal on a switch. The important thing about mechanical connection with any solder joint is to make sure the wire is effectively immobile while you are soldering. When you take an iron, heated to 600F or so, and put it to copper wire, the insulation will rapidly melt, which makes unspringy wires suddenly go springy.

This is even true for surface mount work. When attaching tiny things, you first solder down the corners of the component, to hold it in place while you solder the rest of the pins. Otherwise you end up chasing your parts around the board with a big glob of solder. This is especially true of tiny, heat-conducting discrete components, as you can easily heat up an 0805 resistor to melt both sides of the part and have it stick to the iron. This is handy for removing damaged parts, but not valid for initial soldering.

When soldering tall components or connectors, I always push the component through the board, and solder one pin first. This way, I can turn the board back over and make sure the connector or component is straight up and where I want it. I learned this the hard way by laying down a 40 pin DIP socket, and merrily soldering it away, only to discover later that I had the socket in lopsided, so I couldn’t actually solder the last few terminals. This is very common when people first mount dual row headers.

In general, make sure your mounting is right, tack the part somehow, and then go and solder all the pins quickly. As a note, this is why I don’t like using those helping hand clamp doodads. People will put a bunch of parts through a board, bend the pins, and then put it in the helping hand and start soldering. Remember, you are working with molten metal. If you heat it again, it will melt, and your part will move.

As you merrily go and solder on the back of the board, the parts hanging off the front (facing toward your workbench) are all moving around and falling out as you work. Even though you may have lovely solder joints on the back the front will resemble a cartoon city after an earthquake, with parts leaning every which way and that. It doesn’t look good, and it makes it hard to replace things. This is not a problem so much if you do surface mount work, but it’s nonetheless something to keep in mind.

Third: Applying solder

Once you have tinned your wires (if necessary), and made a strong mechanical connection, you can go ahead and solder. When you melt solder, you see that smoke come off. That’s flux, and it does three important things. First, it cleans off small amounts of crud that can show up on the pads to allow the solder to flow properly. Second, it moves heat rapidly from the tip to the part you want to solder. Finally, it acts to modify the surface tension of the molten solder, enabling it to easily flow around components. Flux is almost essential for working with high pin density SMT parts.

This is why, if you have a big glob of solder on a tip and just start hitting pins with the tip, you’ll end up with gobs of solder stuck to the pins instead of flowing. With no flux to pre-heat the joint, the solder will cool when it hits the pins and will ball up instead of flowing into the joint.

When you apply solder, tin the tip, and then fairly quickly take your tinned tip to the part to be soldered. Ideally, you will see some of the tinning on the tip immediately flow into the joint. If not, don’t worry. Take you solder, and dab it on the hot tip, near the joint you are trying to make. You’ll smell the delightful flux smoke, and see first the flux, then the solder “slurp” into the joint. You want to see that “slurp” action, and your solder joints should look like nice cones on through-hole pins. If you see a little dip where the pin goes through the solder, or it’s not completely filled around, you have a “cold solder joint”, and it will most likely fail. Generally, if you suspect a cold solder joint, you can just go (with your nicely tinned, shiny tip) and just reheat and “reflow” the joint.

I can’t overstate the importance of the “slurp”. When I’m going through standard DIP pins, a joint should slurp in just just about a second. If you find it takes a long time, or you can’t get it to slurp, you need a bigger tip, more solder on the tip when you go to solder, or a higher temperature iron. Note: Higher temperature does not always make things better, as you have to get the heat to both the pin and the pad, or it won’t slurp right. This is why I like using chisel dips, as I can contact the pin and the pad at the same time.

If you’re working with leaded old-school solder, you will see shiny silver domes. Most lead-free solder tends to look a little bit dull and lumpy when dry. It is easier for me to see cold solder joints with leaded solder, and it has a lower melting temperature than lead-free. For this reason, when I prototype stuff, I tend to use leaded solder.

With surface mount, you still want to see the “slurp”, but it’s on a much smaller scale. When soldering discrete components, I tend to tin one pad with a little mound, then hold the iron on the pad until it melts, and then slide the component onto the pad, watching for the “slurp” as the solder sucks onto the side of the component. Once you see it, it’s unmistakable. The slurp is caused by the same things that cause a meniscus to form in water.

Before we go on about tools, one brief thing: If you get into building things seriously, don’t skimp on tools. Buy what you need, but get quality stuff. Lots of people sell these “starter kits” of tools that are a bunch of crappy tools. There’s a reason professional mechanics use Snap-On and electricians buy Klein. I get excited about buying tools. I want to play with them and generally get a good feel for how the tool fits. I tend to look at pawn shops and used tool stores for quality equipment. I’d rather buy used quality tools than new crappy tools, but ideally I buy new quality tools.

That being said, you don’t need to race out and drop $5,000 on a great big box of tools. I’ve been collecting tools, and buying new things when required for years, and now have a pretty reasonable stash of quality equipment. Much of it is old stuff, like my favorite pliers, but good tools will take a lot to wear out.

The Little Red Box

All my small hand tools live in the little red box

As with most of my tools, I need to keep myself easily portable for field work when the job calls. As such, I carry all my small tools inside my little red box. Typically when I am working in the field I take the type of equipment I expect to use on-site. Most of my hand tools fit inside two Craftsman tool bags, but things like tiny screwdrivers and tweezers get lost and crushed when put inside a bigger bag with crescent wrenches and hammers. Hence, the use of the little red box. Originally, this box had a small socket wrench set, but for the last decade or so I’ve had this box full of tiny useful things. This box gets tossed into my bigger tool bags. I’ll give you a tour through my Little Red Box, describing its contents, their use, and where I got it. This article is supposed to deal with soldering, and you will find that much of what is in the Little Red Box is directly applicable to this purpose.

All my common tiny tools, on display

The contents of my little red box fall into seven categories:

1. Tools to hold things
2. Tools to strip and cut things
3. Tools to sand and clean things
4. Tools to screw things
5. Tools to write with
6. Random necessities
7. Tools to scratch, clean, and gouge tiny things

Nearly any time I am working with electronics, I’ll probably have the little read box open and available. Having a hinged lid also helps, as I can use the open box as a tool stand if I need a place to stand up other tools while I’m working.

Tools to hold things

Tweezers and small pliers for holding things

When soldering or working with any small things, having good small tools is important. Above is a picture of my pliers and tweezers. The top is a biggish pair of needle nose pliers- These are my favorite tool, ever. I got these when I was like six years old from a rusty old toolbox in my grandfather’s basement. They’re Klein, more than 40 years old, plain, and very useful.

I use these pliers for bending wires and connectors, as a heatsink for holding components, and as pliers for general work. Note that these are quite beefy for needle nose pliers. I use the fatter flat part at the back for forming pins, and the front for pulling parts out while desoldering. I have kit full of several sizes of smaller needle nose pliers, but in general the jaws are too flimsy for a lot of the work I need to do. I also use these a lot of fishing out screws and holding tiny nuts. I don’t like spring-return needle nose pliers, but that’s probably just because I’m used to the way I hold these.

The bottom two pairs of tweezers are just crappy $3.00 tweezers from a surplus store. I use these for wire bending and holding components. Notice that one is bent wide than the other. I tend to use the wider ones when working with bigger packages, and the smaller ones when working with smaller components. Eventually I’ll get some new tweezers to replace these.

In the middle are a new discovery, suggested by my neighbor, when we were wondering around the other night shopping. These are beauty tweezers meant for plucking hairs manufactured by Tweezerman. These have a ground and rounded front tip, and are probably the most epic tweezers I have ever used for surface mount work. They don’t open up enough to pick up QFPs and such, but for discrete caps and resistors, these are fantastic. I may go back and get another pair from TJ Maxx, as they were on sale for $8.50. Apparently, they have a lifetime sharpness guarantee which means they’ll re-grind the tips if you need them done. Tweezerman also make a slant-tip version of these, and some extremely fine point ones as well.

Tools to strip and cut things

Tools used for stripping and cutting

That’s it. I’ve got a cheap pair of red-handled wire strippers, and a small pair of wire cutters. I’ve tried lots of different ways to strip wire, and for most small wire these red-handled ones work great for me. These aren’t for everyone. I’ve developed a feeling for stripping wires of all kinds of sizes with these, where I can just feel where the insulation tears and get a clean strip on coax, telco cable, Cat5, and many other cable types. I do have other tools for stripping, but I find those red-handled combination stripper/cutters to be among the most versatile, hence the reason they are in the little red box. I just did a brief search to find someone who sells these, but apparently even Radio Shack has changed their cheap basic wire stripper.

On wire cutters: Don’t cut screws, bolts, or really thick solid wire with these. You’ll blunt the cutting edges, and you’ll end up either bending the wire or just denting it. I’ve got a set of big angle-cutters in my tool bag I use for larger wires, and I use these smaller ones only for IC pins, small scale wire, and cutting my 0.1″ headers down to size. You could possibly cut your toenails I guess, but don’t use your small wire cutters for cutting PC boards, screws, non-copper metal, thick plastics. If you leave a dent when you try and cut it, you need to use a different tool. Also, they’ll last longer if you tend to cut towards the back where the hinge is, rather than at the front of the jaws.

Tools to sand and clean things

Sanding and cleaning tools

That’s two strips of sandpaper of different grits, a pencil eraser, and a partially broken emery board for finger nails. You may be asking why I keep these things in my little red box: Connectors and magnet wire. If you ever need to make things out of enameled magnet wire, you will find that it cannot be stripped. You need to sand the wire to get the enamel off.

Also, having sandpaper on hand is generally very handy. You can use it to clean up holes in plastic, sand down a circuit board to fit inside of a slightly too-small box, and use it to clean up rusted or fire-damaged connectors in a pinch. I was on a service call once fixing a device that had been severely water damaged. This device took plug-in modules with edge connectors, which we fixed back in the shop. However, we couldn’t get a new wiring harness on site in time to get the customer’s equipment running, so I used the sand paper and emery board to clean corrosion off the inside of the edge connectors would mate properly. That’s the main reason I keep that emery board in there- It’s just about the same width as a standard circuit board, and can be used to clean out card edge connector sockets (think ISA and PCI connectors).

Also, the pencil eraser. Pencil erasers can be used to do any number of useful cleaning tasks. This eraser has been in the little red box since I was in high school. Pencil erasers work great to clean card edge contacts. They can also be used to clean up flux and goo from a solder pads when a component is removed. They can also be used to erase pencil markings, should you ever have to do that.

Tools to screw things

Tools used to tighten and loosen things

To keep my tiny screwdrivers from getting crunched, they also live in in the little red box. I’ve got multiple sizes of flat and Phillips head. The reason I have several is that these are common “loaner items” when working with other people, since no one ever seems to have a small enough screwdriver to tighten up the wire on that terminal block.

As a note on screwdrivers: It may seem like a good idea to get one of those all-in-one micro screwdrivers with a bunch of bits that snap into a handle, but unless the bits are quite long, or the shaft is quite narrow, you will find that the actual screwdriver tip will not always fit all the way in to the terminal block you are trying to tighten.

Also in here, at the bottom, is my wire-wrap tool. I haven’t done wire wrapping in a while, but of note is that the back of th wire-wrap tool comes off to reveal a very tiny wire stripper for wire wrap wire. I can’t strip wire wrap wire with most other tools, but the little slotted piece of metal works great. I keep spools of wire-wrap wire around, as it’s the only thing on rolls that I have found the is small enough for doing emergency PCB trace repairs on fine-pitch components.

I have a separate case full of tiny jewelers screwdrivers if I need to work with tiny hex/square/whatever types of screws, but once again, in terms of versatility and use, a couple of small screwdrivers will work fine. Some of these are actually Craftsman, and I prefer longer-shanked tools (such as those at the top) verse smaller shanked tools (the two transparent handled ones in the middle), as it allows more finger room for maneuvering.

You’ll note also that these aren’t prybars. Fight hard to use your small screwdrivers to pry, dig, scratch, or gouge. Tightening screws with a bent screwdriver is very annoying.

Tools to write with

Pencil, pen, and Sharpie. Absolutely essential.

It should be obvious to have writing tools, but this is a particularly useful set of things to have. The Sharpie will write on anything, including black-shelled connectors. I often use a single Sharpie marker swipe to denote Pin 1 when I am working with prototype connectors. You can also use the Sharpie to mark on otherwise unknown wires to remember where they go when taking things apart. I tend to mark one slash, two slash, etc on connectors on boards that otherwise have no easy way to label.

Also, when pulling wires, a sharpie can be useful to mark bundles. Just write the number of the wire on one end before you pull, and you can do up the more precise and proper labeling methods after the wire is pulled.

The pencil is a normal old-fashioned wooden lead pencil. This has several tasks beyond making pencil marks. Notice that this is a wooden body with a rubber tip. I often use the pencil as a “probulator” to poke around in operating circuits. Pencil erasers are not conductive, and if you are looking for a cold solder joint on a surface mount board, you can exert quite a lot of spongy-force with the eraser on the end of a wooden stick. Don’t go sticking pencils in high voltage enclosures, though, as it’s not a particularly safe thing to do.

The other benefit of a plain-old wooden pencil is that it is conveniently filled with graphite. Graphite can be used to fake resistors if you are really desperate (Ever wonder what’s in a “carbon composite” resistor?) A friend of mine from Australia was using pencils as current limiters in a battery charging circuit, which I found charmingly cool while simultaneously being very dangerous.

We’re not done yet: Graphite is also an excellent (and mildly conductive) dry lubricant. Those of you who did pinewood derby cars are probably familiar with this. You can make rough-feeling locks run smoother by grinding pencil lead into it. Also, if you ever have to take apart and repair a rotary switch or pot, you can just scribble all over the element with pencil lead to keep it limping along. They make actual lubricants to do this, which I also have, but in a pinch, a pencil works well.

Random necessities

Random necessities to have around

In that bag is a small number of random lengths of heat shrink tubing. A roll of electrical tape rolls around in the tool bag, but I keep an assortment of small-size heat shrink for emergency on-site connector repairs. Sometimes you just can not fit electrical tape around what needs to be fixed, so heat shrink is great to have around.

The lighter is primarily there to shrink the heat shrink tubing, but it can also be used to light torches or offer fire to cigarette-smoking co-workers. In the center of the photo is a random length of desolder wick, which I have also used as emergency grounding strap. Next to that is a couple of random tangles of solder. I keep another small roll of solder in the bag with the plug-in emergency iron, but this is in case I forget that bag or need to do something silly.

Tools to scratch, clean, and gouge tiny things

Dental picks and tiny things to scratch and gouge

Dental picks. They come in all kinds of handy. I actually asked my Dentist for these, and he gave me a stern warning about “not using these on my teeth”. Dentists can only re-use dental picks so many times before they become dull.If you are a dentist, I’m sure you can name these all by their particular names. I use these to clean, scrape, and generally gouge small things when needed. Having a sharp dental pick is great if you need to scrape of circuit board traces (where a utility knife is too big), or mark a whole on something that is too deep for a pencil or other marking device.

I also use the picks to clean up messy solder jobs, or scrape away solder mask to make emergency solder pads when doing circuit board emergency reworking. They also come in handy for getting that tiny little screw out of that annoying corner you just dropped it into, as well as holding down ornery fine wires while trying to solder.

What is soldering?

Soldering is a way of joining metals by melting a low-temperature metal to fill the space between parts. Soldering has been around for a very long time, being used early in copper-making and stained-glass work. Soldering is also used to join copper pipes in plumbing. This article will focus on soldering for electrical assembly.

Soldered 44-pin flat pack

Up until the late 1990′s solder for electronics was made out of tin and lead, and filled with flux. Today, most solder you can buy new is “lead free”, and is made out of Silver, zinc, tin, gold, and other non-harmful metals. I keep stocks of both lead-free and leaded solder. I prefer to work with leaded solder, as it tends to make more “shiny” joints and has a lower melting temperature. Because of this, it is easier to find bad solder joints with leaded solder. All solder has some sort of flux to aid in cleaning contacts and heat transfer.

If you are fixing things (or building things) that need to be RoHS, remember to use lead-free solder.

Basic Soldering Equipment

I can assemble everything from through-hole to surface mount (except BGA’s) using very common tools. I’ve been using the same tools for almost a decade, and sometimes add new things as the need arises.

For soldering electronics, I recommend the following:

1. Soldering Iron
2. Cotton rag/ old pair of jeans / apron
3. Soldapullt
4. Rubber sheet
5. Solder wick
6. Solder
7. Patience

I think it goes without saying that you should have a very well lit area to do electronics work. Also, it’s really nice to have a quasi-permanent spot to spread out your stuff while you assemble.

If you are planning to do work with SMT components, I suggest you wear a machinists’ apron. It’s much easier to find a dropped 0805 chip resistor that falls in the apron when you are sitting down, than to find one that falls between your legs, bounces off the chair, and ends up getting lost in your carpeting / heating vent / whatever.

This is especially annoying if the part you accidentally crush with your rolly-chair is your your last mini-MELF diode, and now you have to go kludge up a 1N4148 standing sideways off a board that now will no longer fit in the enclosure you just spent three hours making.

Also, my apron (which I sadly recently had to retire) was an excellent type of thick cotton which was very good for soldering iron tip wiping.

My portable soldering equipment.

Soldering Iron

In a pinch you can solder with flame heated pieces of metal. I have done this when MacGyvering up an emergency repair, and it is not easy nor fun.

When I first started building things in elementary school, I used an AC-plug Radio Shack style iron. My first experience was terrible, as I proceeded to melt connectors, burn my hands, nearly light a table on fire, and generally destroy everything I tried to solder. My old-time engineering mentor looked at some of my work, saw my soldering iron, and said: “That thing’s a piece of crap”.

In general, if your soldering iron has tips that screw directly into the end, a trigger and little light bulbs, or terminates directly in an AC line cord, you probably have a lousy soldering iron, or the wrong tool for the job. Unless you’re working on pre-1970′s tube-based gear, stained glass, jewelry, or plumbing, you should have a soldering iron, not a soldering gun. Soldering guns look like pistols, with a trigger and sometimes little light bulbs. Soldering irons (or soldering pencils) look like a pencil, and you should hold it like one.

I do keep a cheap hardware-store plug in soldering iron in my my “go kit” that I take on site, but if  I will be doing a lot of soldering, I bring my trusty Weller WES50 iron. The WES50 has apparently been replaced with the WES51, and they cost around $100. You don’t have to go crazy on digital-display USB-connected hot-air rework stations to do quality soldering, although it can make it easier. Nearly everything I’ve built since 2000 has used this Weller iron, and it’s never let me down.

My trusty Weller WES50

The Weller has very rapid and constant heat control, and very nice easy-to-change ESD-safe tips. The Weller (and several other quality brands) have a collar that fits over the front and the tip. This prevents the tip from unscrewing due to temperature changes, and makes tip changes much easier. It also puts the temp sensor right up near the tip where you need it, so they don’t overheat like cheaper irons do.

The Cotton Rag / Old pair of jeans

Soldering iron tips get dirty, due to flux, heat, and just being out. You need to wipe them off, and quite frequently, or else the solder will not stick right to the tip, and you’ll have a hard time making good connections, especially when working with surface-mount components. Most soldering stations (including my Weller) come with a little wet sponge for this purpose.

I’m not sure what brilliant person decided that wiping a 600 degree soldering iron tip on a wet sponge was a good idea, but at this point I’ve entirely given up on “wet sponge” as a soldering iron tip cleaner.

When I started, I used the little sponge, and thought it was the best way to go, primarily because everyone else seemed to do it that way and it made a satisfying “sizzle” sound each time I wiped it. At one point, I lost the little sponge, and started wiping the soldering iron on my “shop jeans”. I noticed that the tip cleaned up really nice, and it stayed tinned longer and wore out slower.

Since then, I’ve given up on sponges. For the last several years, I have been using linen rags (think thick handkerchief) for wiping my soldering iron. I find that jean material (or linen) has the right amount of “scour” to clean the tip, and when rested over my pant-covered leg or chair’s armrest provides the optimum amount of pressure. Don’t use fluffy towels, as you will end up scorching the fluffy bits. Also, don’t use anything plastic / nylon / elastic, as you will find hot soldering iron plus plastic results in a phase-change (it melts or burns).

There are other good ways to clean tips, including copper wire wool (that fits in the little place where the sponge goes) and special sponges and tinning dips. In general, do not use anything harder than the tip (such as steel wool), as you’ll remove the plating on the tip and the solder won’t behave correctly. People still look at me odd when I habitually wipe my soldering iron on my pant leg, but it does make for a clean tip.

Soldapullt

You could go spend a bunch of money on a hot-air vacuum / blower rework tool, or you can go drop $20.00 on a DS017 Soldapullt. The Soldapullt is a blue tube with with a spring loaded-plunger, a plastic bumper on one end and a white tip on the other. The plastic bumper on the spring-loaded side is for banging on a table, and the white end is for sucking solder. If you want to remove solder from a pin, or clean a via or hole on a board, no other cheap tool works better than the Soldapullt. You push the yellow-bumper end against the table until the tool is cocked. When you want to remove solder, you push the yellow button to make the tool go “slurp” and vacuum up the solder.

Once again, I started with a red-squeeze bulb Radio Shack desoldering tool, and had nothing but sorrow. The tip would get too hot, and the suction just was not enough, so  I would end up destroying pads and pealing up traces. With the Soldapullt, you heat up the joint and then just put the white tip close by and hit the button, and bam, you’re left with a clean hole or a free pin.

You can buy smaller tools which operate on a similar principle, but they’re really not worth it. The Soldapullt DS017 is big and beefy, and pulls probably twice as much air as the smaller types. One suck, and you have a clean hole, versus multiple suckings with the smaller ones. You can easily take it apart every once in a while and tap out all the little solder pieces that collect inside. I’ve actually worn out two of these tools so far, and find they are well worth the $20.

The Soldapullt comes in handy when doing surface mount as well.

Rubber Sheet

Some may call this an “anti-static mat”. That’s what mine says. I pulled it out of a dumpster some time ago, washed it off, and have been using it ever since. I’m not terribly concerned with static in my work environment, and I have yet to damage anything due to static discharge. Having a rubbery work surface is more useful to me as a device to self-clamp the part to the table.

In my early days, I had one of these multi-armed alligator-jawed things, and found it slightly annoying. They never seemed robust enough to hold anything, or else setting up to solder took too long, so I started soldering on the tabletop. This mean I found myself chasing the part around the table, as I tried to hold a component down and solder at the same time on a slick wood surface. The grabbiness of the rubber static-mat is enough to keep the boards from sliding around the table.

As another benefit, my rubber anti-stat mat doesn’t easily melt or char. For a while I was using a self healing cutting pad or a piece of wood to protect my table top, but the cutting pad would melt, and the wood was just a pain. The mat I use came from the garbage, but it’s about the same size and construction type of this $60.00 one from Digi-Key. When I’m using my workbench for drilling holes or dismantling things, the static-mat gets rolled up and stuck on a shelf.

The only time I pull out the vice is when I am desoldering massive through-hole components (like big power connectors, that take lots of heat and some yanking), which require me to work both sides of a board at the same time.

Solder Wick

Also known as desoldering braid, is very similar in appearance to the woven shield of high quality cable. It’s basically a think, flat, fine-thread braided cable which is usually somehow coated or dipped in Flux. Some people swear by the stuff, but I very seldom use it.

Solder braid is very useful for cleaning up pins on SMT devices after soldering. It takes some skill to use, as improper use of heat can end up soldering the solder braid to the part you are trying to work with, resulting in a mess. Additionally, solder wick tends to take a lot of heat to be useful, which means you can overheat components with too generous use.

In general, solder wick is used to wick up solder, like a ShamWow soaks up stains and spills. It’s good to have a spool of this around, and I have used it to clean up pins that I have (1) made a mess out of, or (2) has been made a mess out of by someone else. I discovered the “table tapping” method for doing similar tasks to what solder braid can be used for, but some people may be horrified by seeing this trick in practice.

Solder

I bought a big pound spool of solder from Digi-Key several years back and still use it. I recently bought another pound spool of lead-free solder for doing work which needs to be RoHS. If you go to the hardware store, make sure you get “electrical solder”. The kinds of solder used for plumbing, body repair, stained glass, or jewelry are made out of different metals for their particular applications. Also, fluxes very widely for various applications as well.

I like .032 diameter solder. Some people prefer it thinner, but I find that thinner solder just goes faster, and needs more work from me to feed correctly. My SMT skills use the “drag” method of soldering, in which I’m not trying to hit every pin with the solder. In general, I get the solder on the tip of the iron, and then use the tip to apply it to the leads, so the actual solder width is not tremendously important.

That being said, if you get really thick solder (once again, the kind that would be used with your front-headlighted soldering “gun” for 1950′s tube equipment), even the slightest touch of solder and soldering iron will flood your tip with a giant ball, making accurate soldering very difficult. A little solder goes a long way, and unless you are assembling circuit boards for a living, try and get a smallish size and stick with it. I have a little tube of “emergency solder” in my go-kit, which is basically a mini-roll of my main solder spool rolled up and stuff inside of an old electrical-tape container.

Patience

Soldering takes time and patience. More on this on Part 2:  How to Solder. Start out with soldering through-hole components, and whenever you buy parts, unless they’re really expensive, buy two. The first things to learn how to solder are connectors (go build yourself a serial cable for something) and inter-board 0.1″ type wires, to connect your neat Nixie Tube drivers to your Arduino PCB controller.

I advise against rushing out and getting a bunch of 144 LQFPs and starting with that.

The first project I ever soldered was on the back of radio shack pad-per-hole perfboard, and used a 555 timer, a counter, and a BCD to LED driver to count from 0-9 and reset. I probably rebuilt that circuit four or five times before I got one the wasn’t hideous.

My standard stock of pin headers and banana connectors

The Basic and Versatile: 0.1″ Pin Headers

0.1″ pin headers are almost universal on dev kits and sample boards, so it would serve you good to have some around the shop. A standard old-school 40-pin IDE is a dual row 0.1″ pin header, and things like the Make Controller and many Arduino kits use this same style of connector.

Pin header assortment, male and female with example

Above is a hand-soldered level converter board I put together in a pinch, featuring 2x 5-pin male pin headers with heat-shrink on the female connector. The male connectors I used are  Digi-KeyPart Number SAM1059-50-ND “CONN HEADER 50POS .100″ SNGL TIN. I buy them in the 50-pin length, and then just cut off the number of pins I need. Pin headers are available with a number of different lengths of pin, but I tend to buy longer ones, as you can always cut them shorter if need be. Also, having longer pins means you can easily bend them to make odd-angled connectors if you need to. The photo shows examples of the raw pin header, as well as the female header to which it mates.

When using the female headers, Digi-Key # S7034-ND “CONN HEADER FEMALE 36POS.1″ TIN”, you will always lose a pin when cutting them to length, as the female headers do not have the space between them that the male pin headers do. You can get these in various lengths as well, with the above being a 36-position. It is worth noting that these female headers can mate with various types of male connectors, including MTA-100′s (as discussed below). You can also stack two of these together to mate with dual-row headers, if you need to jury-rig up a JTAG cable harness or what have you. They also can be used instead of jumper blocks for equipment which uses 0.1″ jumpers for configuration. You can also stack circuit boards using these connectors.

I wouldn’t recommend these connectors for anything above a few 100 mA. Small stepper motors are okay, but for higher currents use MTA-xxx or screw terminals. Pin headers have very small actual contact areas, when compared to other styles of connector. Don’t use them for applications which need many reconnection cycles, as the pins eventually will wear out. They will also vibrate loose. I use these a lot, but never in a production environment unless used to stack boards where other physical locking systems can be used.

When soldering either of these, make sure you tin the pin and the wire before you solder. People tend to keep heat on these plastic solder-on connectors for too long, which results in the pins coming lose of the male headers, or the plastic enclosure melting on the rectangular header. Even when done properly, the resulting joint will be quite weak, as there is no strain relief on the wire. This is fine for prototyping, but if you want something that will last longer, use some heat shrink, or upgrade to MTA style connectors,as discussed below.

More Strength: MTA-XXX connectors

For those applications that need:

1. Locking Connectors
2. Higher current
3. Basic strain relief
4. Vibration resistance

I suggest the use of MTA-xxx style connectors. I keep two styles on hand, MTA-100 and MTA-156. The MTA-100′s have the same pin spacing as the basic pin headers above (indeed, female MTA-100′s can mate with male pin headers, and female pin headers can mate with male MTA-100′s). MTA-100′s feature a strain relief on the wire, and they can therefore be used in high-temp and vibration prone environments. MTA connectors are very commonly used inside equipment to bring wires to chassis connectors and front panels, or internal wired interconnection. Their locking mechanism is quite robust, and I have had excellent experience with them. You can not easily slice MTA-100′s to the appropriate number of positions due to the presence of the locking mechanism. The following photo shows an application of MTA-100 connectors on the prototype FEC motor drive “cube” I built in college.

Example of MTA-100 connectors used on prototype.

The MTA-156 connectors have a 0.156″ pin spacing, instead of the .1″ as in the MTA100, which means MTA156′s will not fit in standard PCB protoboard without drilling and mucking about. However, MTA-156′s are rated to 7 Amps, while MTA-100′s are rated to around 3 Amps.

MTA-XXX style connectors are IDC (Insulation Displacement Connectors), which means they have little teeth that rip through the insulation when the wire is inserted. Wire size with IDC connectors is extremely important. If you cram an over-sized wire into any IDC connector, the connector will be damaged and the crimp will fail. Same thing with putting small wire in an over-sized crimp. They also need a special tool to easily assemble, as discussed below.

The different sized MTA connectors are color coded  (RED = 22 AWG, GREEN = 28 AWG, WHITE=24 AWG, etc) for ease of use. 22 AWG is the largest wire size supported by MTA-100 connectors, so I keep a stock of those around in the interest of versatility. If you want to use crimp ends, buy wire of the proper size, or they will give you nothing but trouble. You can’t use old Ethernet or Serial cables in a 22 AWG Red MTA-100 crimp, as the wires will fall out. If you try and solder these, chances are good they will fail. You’re better off using the 0.1″ pin header for found wire and cable.

If you are installing hundreds of these connectors, you should drop the several hundred dollars on the neato ratcheting MTA-crimp tool- Digi-Key #58579-1-ND, “TOOL HAND MTA 100″ This is a really nice ratcheting tool that lets you put these together very quickly and very reliably. However, it’s tremendous overkill for most hobbyists. A significant benefit of using MTA type connectors is that the kind people at Digi-Key sell $20.00 t-handle tools for both the MTA-100 and MTA-156 style connectors. This produces a crimp on par with the ratcheting tool, but it is slower and more tricky. The MTA-100 T-handle tool is Digi-Key #A9982-ND and the MTA-156 is #A9981-ND. The availability of this silly tool is why I highly recommend MTA style connectors over other crimp-terminal style connectors.

Some people prefer individual crimp-pins that slide into plastic housings. I find these to be terribly annoying, as properly crimping on the pin for most of these types of connectors is very difficult without the proper tool. The MTA type connectors from Tyco are a very good compromise of robustness vs. cost of installation tool. In a pinch, you can use a flat-head screwdriver and get a high quality crimp, if you do it very carefully.

MTA connectors with low-cost insertion tool

The photo above shows (from left to right), an MTA-156 pair side view, an MTA-100 front view, a wire assembly made with the T-handle tool, and the T-handle MTA-100 tool.

Banana Jacks: Whoooo boy!

Banana jacks are used on most bench power supplies, and DVMs. The far right photo shows my assortment of connectors and things I keep on hand, and one bin is full of screw-on banana jacks. I have sets of banana-jack jumper cables, but for interfacing my power supplies and other banana-jack equipped test equipment to my prototypes, I make extensive use of screw-on stackable banana jack ends. I find this much cleaner and easier than using binding posts and raw wires, as it means I can rapidly string things together or reconfigure my power supply equipment to measure currents.

The ones I really like are set-screw based Banana jacks: Red (Digi-Key #501-1077-ND) , Black (Digi-Key #501-1076-ND)  and Green (Digi-Key #501-1247-ND). Get a bag, and then you can make banana-jack jumpers to your heart’s content.

My name is Greg Linder, freelance engineer and consultant. I’ve got an MSEE from Clarkson University and a BSEE from University of Illinois. Ever since I was in elementary school, I have been building, fixing, taking apart, and re-assembling. Through most of my education, friends have asked me questions about things ranging from “Does this PCB layout look any good?” to “How do I solder a surface mount QFP?” (You don’t need an air gun). This web page is meant to be an outlet for common prototype-construction questions, including photos and examples, from my career as a freelance inventor and engineer.

Topics will range from soldering, to component selection, to proper shop tasks and my experiences with various types of test equipment and tools. As readership develops, I’ll answer questions put to me in the realm of general construction whenever I am able. The motivation here is to help inventors and electrical engineers get a feel for the merits and requirements for hands-on engineering. Lots of people want to build, but are never taught how to solder or lay out a circuit board in engineering school, those topics typically being “tradesman” type topics. Well, if you want to prototype things yourself, you’ve gotta know how to make good looking enclosures, fix circuit boards, and repair SMT stuff in a pinch.

As an engineer, I believe deeply that engineers should never design things without having first repaired or serviced a similar piece of equipment, or at least taken something apart and put it back together again. This is my effort to cater to those who want to tinker on their own, either for work or for fun.

The articles written here are my own opinions. Use the information at your own risk. I’m not responsible for how you use this information, or how the techniques discussed work out for you. Whenever I can, I’ll include links to vendors’ part numbers and the like, to facilitate easy adoption of some of my neat tricks.