Monday, July 7, 2014

EastBay RC Guide to Soldering


This are the notes and videos for a two-hour introductory soldering class.  It's designed to be taken Khan Academy style -- watch the videos and read the notes first, and we'll be able to spend the entire class on soldering.
  • Hands-on class, two hours.
  • Time: 15 minutes, intro and tinning soldering iron; 15 minutes, tinning wire; 15 minutes, soldering thicker wires; 10 minutes, soldering thinner wires; 30 minutes, soldering PCB; 10 minutes, heat shrink; 15 minutes, soldering pads.
  • Watch the videos first, be ready to practice in class.
EastBay RC is a continuing work in progress. Let me know what you think!

Here's all the videos as a playlist.  Watch it in HD, it will be a lot clearer.  I'm trying to figure out how to specify that an entire playlist should be shown in HD.  If you know how to do this, let me know! Individual videos are down below.

  • Soldering irons are hot. Molten metal is hot.
  • Pay attention. Don't grab hot stuff.
  • Don't splash molten metal into your eyes.
  • Don't cut wire and shoot wire bits into your eyes.
  • Wear safety goggles or safety glasses.
  • If you're working next to an unsafe idiot, move away to safety.
  • Lead, in case you haven't heard, is toxic.  Wash your hands when you finish.  Don't eat it. Don't eat, handle food, or smoke while you're handling lead.
  • The smoke from soldering is not lead.  It's from the resin, typically made from tree sap.
  • If you're working next to an unsafe idiot, move away to safety! (ht: Brian Green)
Reasons for Bad Soldering.
  • Bad iron.
  • Bad solder.
  • Bad tip.
  • Low temperature (see bad iron).
  • When you touch the solder to the tip of the iron, it should melt easily and immediately.
  • "painting" solder onto surface instead of letting it flow.
  • Soldering over old tinning.
  • solder -- 60/40 lead based, rosin-core.  Avoid lead-free for general electronics use -- it has a higher melting point and is difficult to hand solder. 0.8mm is good for general electronics use.  0.5mm is good for PCB use.  Any size actually works, it's just a bit easier to feed the right amount. Kester is a good brand.
  • cleaning sponge or pad.  Dampen but don't soak the sponge.
  • side cutters
  • wire stripper
  • "helping hands" unit
  • heat shrink
Some Good Soldering Irons.
Soldering Concepts.
  • Solder flows toward heat -- heat the wire, not the solder.
  • Flux -- cleans the surface, helps solder flow.
  • Temperatures -- 700 degrees F is a good average temperature.
  • Don't use plumbing flux, it's acid based.
  • Keep the tip clean.  It should "wet" easily.
  • When finished soldering, melt some solder on the tip.  This keeps it from oxidizing.
  • Solder over an old piece of wood so you don't drip solder on your nice workspace.
  • Weller guide to soldering.
Soldering Speed and Heat.
  • Almost all solder joints are made in just 1-2 seconds.
  • If you can't heat your surface in that time, something is wrong with your iron, or it is underpowered for your job.
  • When you touch your iron to your solder, it should melt and the rosin should smoke immediately.  If not, your soldering job is going to fail.
  • If you keep the soldering iron applied for too long a time, you can melt your insulation, damage your components, or cause a PC board to delaminate.
  • Assignment: inspect iron, power on, clean tip, tin tip. Confirm your solder melt.

Tinning a Wire.
  • Putting solder on a wire/surface before attaching it to something.
  • Basic idea: tinning "wets" the surface, making a solid electrical connection; then the solder on each surface flows together easily.
  • PRE-TINNED WIRES WILL MESS YOU UP.  Especially if it's been tinned with lead-free solder.  You'll get a good physical bond, but a poor electrical bond.
  • Snip away any pre-tinned wire or wire not in good condition.
  • Strip the wire.
  • Twist the wire into a tidy spiral.
  • Form the heat bridge by putting some solder on the hot iron.
  • Touch the heat bridge to the wire.  This will start heating the wire.
  • Touch the solder to where where the heat bridge is touching the wire.  This will start the solder flowing onto the wire and into the strands.
  • Move the solder up the exposed wire, letting it melt and flow into the wire.
  • This should only take 1-2 seconds.
  • Assignment: tin a wire.

Soldering Thicker Wires.
  • Strip the wires, removing any old tinning if necesary.
  • Twist the wires together tightly.
  • Put into the helping hands.
  • Form the heat bridge by putting some solder on the iron.
  • Touch the heat bridge to the wires.
  • Touch to solder to the point where the heat bridge is touching the wires. This will start the solder flowing.
  • Move the solder up the wires, letting the solder melt and flow into the wires.
  • This should only take 1-2 seconds.
  • Assignment: solder two wires together.

Soldering Thin Wires.
  • Sometimes it's hard to twist the wires together if they're too thin, or if they're in a tight spot and you can't pull them out.
  • Tin each of the wires, with a generous amount of solder.
  • Touch the wires together using the helping hands.
  • Touch the iron to the wires.
  • The solder in the two wires will flow together, bonding the two wires together.
  • This should only take 1-2 seconds.
  • Assignment: solder two thin wires together.

Insulating with Heat Shrink Tubing.
  • Be sure and put your heat shrink tubing on your wire before you solder it if necessary.
  • Let the solder joint cool.
  • Move the heat shrink tubing over the solder joint.
  • Heat the tubing with a heat gun or lighter.
  • The tubing will shrink onto the solder joint.
  • Let it cool and inspect for a tight fit.
  • Assignment: insulate the wires you soldered together previously

Through-Hole Soldering onto Printed Circuit Boards (PCBs).
  • Make sure your component is lined up and stable.
  • Use skinny solder if you have it; it will give you more control.
  • Make a heat bridge on your iron.
  • Touch the heat bridge where the component and board intersect.
  • Touch the solder to that joint and move it to the side opposite the iron.
  • The solder will naturally flow between  the PCB and the component.
  • This should take about 1-2 seconds.
  • The result should like like a hershey's kiss.
  • Check for "cold" or "dry" joint, where the solder doesn't make clean contact with the PCB and the component.  "Ball shaped" is bad. Gaps between the component and PCB are bad.
  • Cut off any excess from the component with a side cutter.  Be careful, don't let it shoot towards your eye!
  • Assignment: solder some pins onto a PC Board.  Fill up a board! Compare the first and last ones, and marvel about how much better you've gotten.  I did 725 in a couple of evenings and ended up feeling pretty confident that I wasn't going to destroy any projects with a bad solder job.

Attaching a Wire to a PCB Solder Pad or Flat Surface.
  • Tin the pad on the PCB.
  • Tin the wire.
  • Put the wire on top of the tinned pad.
  • Touch with soldering iron.
  • Let solder flow together.
  • Should be 1-2 seconds.
  • Assignment: solder a wire onto a Solder Pad

  • Sometimes you need to clean up old solder.
  • Disassembling an old project.
  • Cleaning up a soldering mistake (bad joint, incorrect connection).
  • Braided solder wick is made from copper and has resin internally.  Put it on errant solder, make a heat bridge and "soak" up the errant solder. Trim off the wick that has absorbed solder.
  • A solder pump (aka "solder sucker) works well for cleaning up through-hole solder, since it can easily suck out solder from the hole.  Heat the solder directly with the soldering iron, then press the solder pump over the melted solder and click the release button, sucking up the molten solder. It may take a couple of pumps to totally clean the solder away.

Bonus: Soldering Bullet Connectors
  • Snip the wire if necessary and tin.
  • IMPORTANT, see above: using a pre-tinned or untinned wire is the main cause of a "dry" or "cold" solder joint.  This will cause a failure in your system.
  • Put the bullet connector upright into a hole drilled into a piece of wood.
  • Put your iron tip into the hole.  Not too tight, or it's hard to pull off.
  • Put your solder inside the "cup" of the connector.
  • Let the cup fill up about halfway with solder.
  • Remove the iron, let solder harden.
  • Re-heat the solder in the cup until it just melts.
  • Insert the wire into the cup, remove the soldering iron.
  • (note: cooling and reheating the solder is optional; it makes the next step quicker.)
  • Carefully hold the wire upright until the solder hardens.
  • The cup should be full, but not overflow.
  • Heat shrink the connector.

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