I. Soldering Basics


Selecting your Soldering Iron
The secret of good soldering is to use the right amount of heat. Too little heat will result in a cold solder joint; too much heat can seriously damage a component. The key factors in quality soldering are time and temperature. Generally, rapid heating is desired. If heat is applied too long, the flux may be consumed and surface oxidation can become a problem.

All soldering should be performed with a soldering iron rated at approximately 45 watts (a soldering gun should never be used on electronic components). A soldering iron tip size of around 1/4" or 5mm works well for most R/C applications. The tip should be kept clean by brushing it frequently on a moist sponge. You may use an iron that plugs directly into a wall outlet, or for better temperature control, use a soldering station. Soldering stations usually have a variable temperature control which lets you set the right amount of heat to be used.


Figure 1: Soldering station with variable temperature control, solder, and solder wick.

Using the Right Solder
The choice of solder for a particular job is determined by its melting point. The following chart shows the material composition and melting temperatures for three of the common solder types:



The solder type most used in circuit wiring work is 63-37 because this tin-lead ratio provides the most rapid solid to liquid transition and the best stress resistance. Always use rosin-core solder and never use acid-core. The rosin is a flux and flux removes oxide by suspending it in solution and floating it to the top. Flux is not a cleaning agent! The work must be cleaned before soldering. Flux is not part of a soldered connection, it merely aids the soldering process. If you apply too much solder, the excess can be removed with Solder Wick (Refer to Figure 1). Solder Wick is braded copper ribbon and usually comes on a spool. To use it, place the solder wick on top of the solder that is to be removed. You then place your iron on top of the wick. When the solder begins to melt, it will be drawn up into the wick by capillary action.

Solder Joint Basics
Before solder is applied, a good mechanical connection should be made between the wires by twisting the wires together. Soldering should be considered a means for making a good electrical connection, not a mechanical one.

For good heat conduction between the soldering iron and the joint, a small amount of solder should be applied to the tinned portion of the soldering-iron tip, and this surface should be applied to the joint. The solder wire is then applied to the joint, but is not brought into contact with the iron. When the solder melts into the wire, the joint is properly soldered. This procedure avoids a cold solder joint that could cause trouble at some future time. It is a good idea for the inexperienced hobbyist to practice soldering with some scrap wire. The stripped ends of high strand count power wires for the ESC should be tinned by flowing rosin-core solder onto them before soldering them to the battery, motor, or solder posts. This tinning procedure ensures a quick, clean, hot-solder joint.

II. R/C Specifics


Thinning Wires
Tinning wires must be done before any solder joints are made. The following steps should be followed.



Figure 2


Figure 3



STEP 1 : Prepare Wires
The wires that are going to be soldered need to be prepared beforehand. Strip 1/4" of insulation from the end of the wire, and tightly twist the exposed strands.

STEP 2 : Clean and Tin Soldering Iron Tip
The soldering iron tip must be cleaned and tinned prior to soldering to aid in the transfer of heat to the wire end. Wipe the tip on a wet sponge, and then apply a small amount of solder to it.

STEP 3: Tin Wire (Figure 2)

1. Heat the area of the wire to be tinned by placing the tip of the soldering iron along the side of the exposed strands.

2. Apply solder to the wire (not to the soldering iron tip!). When the wire end reaches a sufficient temperature, the solder will melt and the capillary action of the wire will draw the molten solder up into the strands (Figure 3).

TIPS TO REMEMBER:

• Apply enough solder so that every strand in the twisted tip is surrounded by solder.

• Do not over-tin the wire or the solder may flow up under the wire's insulation causing it to become rigid, or you will end up with globs of solder on the wire ends that will have to be removed.

• If you are going to splice the wire to the middle of another wire, strip away the wire's insulation from the area to be soldered to, and tin this exposed area just as you did with the wire end. (Figure 4)


Figure 4

Splicing Wires

Splicing Larger Gauge Wire (Method 1)
The most common method used in R/C to splice power wires is shown in Figures 5 & 6. To splice the wires this way, you would need to strip and tin the end of each wire, and place it side by side with the tinned area of the wire it is to be attached to.


Figure 5


Figure 6

Step 1 : Apply solder to the joint using the same techniques you used when you tinned the wires. (Figure 5). This will form a good electrical connection. However, it won't be as mechanically strong as it would be if the wires were twisted together. This is the method most used in R/C, and is acceptable even though it is mechanically inferior.

Step 2 : Always insulate any exposed wire connections to prevent shorting. You can use electrical tape, however the best method of insulation is to cover the connection with heat shrink tubing. (Figure 6)

Splicing Larger Gauge Wire (Method 2)
If you need a stronger mechanical connnection, then the wires should be twisted together prior to soldering. Twisting the larger gauge power or motor wires together can be difficult. One way to do it is illustrated in Figures 7, 8, & 9.


Figure 7

Figure 8

Figure 9

Step 1 : Strip about 1 inch of insulation from the end of the wire. Divide the strands into two equal parts, and twist and tin each part separately (Figure 7)

Step 2 : Wrap these ends around the tinned area of the wire that you are splicing to (a pair of needle nose pliers will help you to do this). (Figures 8-9)

Step 3 : Solder the joint using the same techniques you used to tin the wire. This will form a strong mechanical connection and also provide good electrical conductance.

Step 4 : Insulate the exposed solder joint to prevent shorting using shrink tubing or electrical tape. (Refer to Figure 6 above)

Splicing Smaller Gauge Wires
When splicing smaller gauge wires, such as switch or receiver harnesses, always tin the two ends and twist them together before applying solder to the joint (Figure 10). Splicing a harness wire will make the spliced wire shorter than the other wire(s) in the harness. When the harness is pulled, all of the shear stress will be on the shorter wire, so it is imperative that the mechanical connection be strong. Be sure to insulate the exposed wire connections (Figure 11) to prevent shorting (refer to above section). Re-twist the harness to take up the slack in the longer wires and improve the overall strength (Figure 12).


Figure 10

Figure 11

Figure 12


Attaching Wires to Solder Posts
The Novak Cyclone and Atom speed controls include low-resistance solder posts for quick installation, clean wire replacement, and unlimited positioning of any size power wire.

Step 1 : Strip and Tin Wire Ends. Strip about 1/8" of insulation from the end of the wire and tin it using the method outlined above .

Step 2 : Apply Solder Bead to Posts. If your ESC is new, there should be a rounded bead of solder on the top of the solder post. If you are replacing the wires, this solder bead is most likely gone and you'll see the flat top of the post. In this case, you will need to re-apply the solder bead to the post. To do this:

1. Clean and tin the tip of the soldering iron, and place it on the top of the solder post.

Figure 13
2. Apply a small amount of solder to the post and then remove the soldering iron (Figure 13). The surface tension of the solder will cause it bead up, forming a rounded mound of solder on top of the post. Do this quickly, being careful not to over heat the post or you may cause the solder to re-flow on the bottom of the circuit board.

Step 3 : Decide Wire Direction(s)

Step 4 : Clean & Tin Soldering Iron Tip and apply a small amount of solder to it.

Step 5 : Solder Wire to Post

1. Place the tinned end of the wire on top of the solder bead on the appropriate solder post--oriented in the desired direction. (Figure 14)
2. Apply the soldering iron to the top of the wire directly above the post and apply gentle pressure. Hold it there until the solder bead on the post melts and flows into the wire. (Figure 15)
3. Remove the soldering iron and hold the wire in place until the solder hardens. (Figure 16) Caution: The wire may become too hot to hold with your bare hands, so you may want to hold it with a pair of pliers.


Figure 14

Figure 15

Figure 16

III. Things to Remember

• Clean and tin the soldering iron tip often.
• Always tin the parts of the wire that are to be joined.
• Whenever possible, twist the wires together before soldering for a good mechanical connection.
• Do not over tin the wires or apply too much solder to the connection.
• Always insulate your soldered connections to prevent shorting.
• Do not over-heat the solder posts.