BEST Soldering Guide

You don't have to take the NASA soldering course to build a winning BEST 'bot, but good soldering will keep your robot running throughout the matches.  Some tips:

Safety First!

The soldering iron and liquid solder are HOT!  A typical soldering iron is 700F.  It is remarkably easy to pick up a soldering iron by the wrong end if you're not paying attention.  Follow the following safety tips:

  1. Solder in a well ventilated area. The smoke from the flux is generally nontoxic, but it may bother some people and may carry trace amounts of lead.  Try to arrange your work area so that the smoke from the solder flux blows away from you and your helper.  Use a fan placed well behind you to generate a slight breeze.  Do not let it blow on the iron or your work as this can cause bad solder joints.
  2. Pay attention to the job at hand.  Do not solder if you can't devote full attention to the job.  Have a helper hold the objects you are solder and hand you things as needed.  You'll have the iron in one hand and the solder in the other.
  3. Do not snap the iron down to flick solder off.  A small flying drop of solder will splatter and stick to your skin.  This will instantly raise a blister that hurts.

Soldering Basics:

  1. Use a good soldering iron.  Select a 25-30 watt iron.  A soldering gun will work but puts out a lot more heat that can easily melt wire insulation and cause shorts.  Radio Shack has a 11 piece kit (P/N 64-2803) with a 30 watt iron, solder and other tools.
  2. Use 63/37 (best, melts at 361 F) or 60/40 (better, melts at 374F), low temperature, rosin core solder.  DO NOT USE ACID CORE SOLDER!  The rosin flux helps clean the solder joint.  Radio Shack P/N 64-005 is a good choice.  This 2 1/2 oz roll should build several years of BEST 'bots.  0.032" diameter solder is preferred, but 0.062" diameter will work as well.
  3. The items to solder (terminals, wires, etc.)  must be clean.  The rosin flux helps, but you need to make sure the joint is clean to begin with.  If they are dirty or corroded, clean them first.  Use a small knife or steel wool to gently scrape any contamination or corrosion to reveal shiny metal.  The terminals on the return kit motors may have old solder and wire on them.  It needs to be removed first.  Heat up the joint and add a little extra solder.  Now wipe the solder off  with a damp (not wet) paper towel or sponge.
  4. Have a damp sponge available.  You will wipe the iron on this to clean excess and oxidized solder off of the iron.
  5. The soldering iron must be HOT.  When you touch the solder to the tip of the iron, it should liquefy immediately.
  6. Strip only enough insulation off the wire necessary to 'sit' on the terminal.   On the final solder joint, the insulation should be about 1/16" from the terminal.  If more bare wire is exposed, it may flex and short.  The insulation should not be in the solder joint.
  7. Generally, it's a good idea to tin the wire and terminal prior to the final soldering.  (Don't do this for the butt connectors.) 
    1. Apply a small amount of solder to the tip of the iron (less than 1/4" of solder, just enough for a wet film to form). 
    2. Bring the iron tip to the wire or terminal.  The solder on the iron tip will wet the wire or terminal.  This is the sign that the object is hot enough to apply more solder. 
    3. Now apply more solder.  A terminal needs just enough to fill in the hole.  A wire needs just enough to fill the gaps between and lightly cover the strands.  In either case, you should not have a ball or a drip forming.  If you do, wipe the iron on the sponge to clean it, then put the iron back on the object to transfer the excess solder to the iron.  Repeat this until no extra solder remains.
    4. When the wire and terminal are tinned, place the iron tip on the terminal.  When the solder on the terminal flows, place the tinned wire on the terminal.  When the solder on both the terminal and wire flow freely together, remove the iron.  Hold the wire steady on the terminal until it cools enough to solidify.  The solder on the terminal should remain shiny.  A grainy texture indicates a cold (bad) solder joint.  If this happens, reheat the joint again.
  8. When soldering or tinning wires, hold them 3-4 inches back on the insulation.  The soldering iron tip is about 700F.  The wires will get hot, even back through the insulation.  A good joint will only take 2-3 seconds to complete.  In this time the wires will heat up, but not enough to cause burns.  You can use pliers to hold the wires while soldering, but make sure that you hold them at least 1 inch back on the insulation.  Grip the wire only tight enough to hold the wire.  Holding the wire too tight or too close to the joint may damage the insulation.
  9. Soldering one wire to a terminal is relatively easy.  The trick comes in getting two wires on one terminal (like on the microswitches).  The best way to do this is:
    1. Strip both wires a little longer than you would have for a single wire.
    2. Twist the two bare ends firmly.  Use needle nose pliers if required.  Twist the wires together all the way to the end.  Do not leave any strands sticking out.
    3. Now, solder tin the wire to the terminal as above.
  10. Rosin flux can be left on the joint.  Normally flux should be clear and yellow to light brown.  If your flux is dark brown or black (charred), you are overheating the joint.  The wire insulation may show a little discoloration but should not be charred.

Soldering crimp connectors:

    1. Strip enough wire to pass thru the metal part of the crimp barrel and be visible between the crimp and connector areas.  The insulation should butt up against the metal crimp barrel inside the plastic crimp area.
    2. Apply the tip of the hot iron onto the wire exposed between the crimp and connector areas.
    3. Apply solder between the tip and the wire.  Use only enough solder to fill the area around the wire and crimp barrel.  You should be able to see the strands of the wire, even though they are covered with solder.

Crimping crimp connectors:

  1. Strip enough wire to pass thru the metal part of the crimp barrel and be visible between the crimp and connector areas.  The insulation should butt up against the metal crimp barrel inside the plastic crimp area.
  2. Use a crimp tool to compress the crimp barrel.  Do not use needle nose pliers or wire cutters as a crimp tool.
  3. Test the crimp by trying to pull the wire from the connector.  You should not be able to separate the wire from the terminal.
  4. If you don't have a crimp tool or can't apply enough force for a good crimp, use the solder method.


Examples of Bad Soldering Technique


If you soldering looks like this, you've come to the right place.  This has just about everything bad.  Both joints are cold, too much wire is exposed and the insulation on the red wire is seriously damaged.  This could very easily blow a fuse when the motor is activated, even during a match.
Both these joints are cold.  Note how the solder doesn't flow evenly over the wires.  Another thing to note is how close the black wire is to the other terminal.  Although this is OK as is, be careful when you solder on the other terminal so you don't damage the black wire's insulation.
This one looks a little better, but again the solder doesn't flow onto the wire or the terminal.


Examples of Good Soldering Technique


The black wire is a good joint. It is very shiny. The red wire could use a little more solder.
This is good connection on the large motor.  Note that the wire's insulation end very close to the terminal.  There are no big globs. 

Be very careful here.   Excess solder can short the terminals to the case and blow the 20A fuse.

Here the solder joints have been insulated wire electrical tape.  These bullet connectors are crimped.  Note the light area on the bullet connectors plastic.

Keep the wires to the big motors as short as possible to limit power loss.

Here the servos and microswitches are assembled into a control switch for the small motors.

Here are some additional links on how to solder:

NASA Soldering Videos
Basic Soldering Guide

How to solder

Please note:  This page is not sponsored by Radio Shack.  They are a good source for basic electronic parts and tools..