|
|
 |
|
|
| Issue 94 (September 2003) |
Words: Mike Velez |
Okay, so you've mastered the art of soldering battery packs together and you're pretty proficient when it comes to getting your motor installed, but what about the hard stuff? You're probably thinking, "That's not hard stuff?" Just because you know how to perform the aforementioned tasks doesn't mean you've got what it takes to say, replace a servo lead on a circuit board, or an LED. Well after reading this article, you'll be ready to tackle any RC soldering task you might come across. This article is not written for the guy that's never picked up a soldering iron before, instead it's intended for the guy that has an iron a basic understanding of how to use it.
|
|
Preparation
Before you begin any soldering job, a few minutes of preparation will save you plenty of time once you get working. First, make sure that the area you're working in is nice and clean. There should be nothing lying around that might interfere with your work. Run through a mental checklist of all the items you might need for the job. Have the components you'll be soldering cleaned, disassembled, and ready to work on. Have your iron pre-heated before it comes in contact with anything. If your iron is temperature adjustable, a setting between 650 degrees and 700 degrees should be sufficient for any RC job when using the correct solder and tip. If your iron is not temperature adjustable, a 35W to 40W iron should be sufficient. Allow your iron a good five minutes to pre-heat before you begin.
The Fundamentals
• Always keep your iron clean. Before every solder application, wipe down your iron on a damp sponge. It's important that the sponge is just damp and not soaked. No special solution is used to wet the sponge; regular tap water will work, but distilled water works best. If the sponge is too wet, it will drop the temperature of the iron and shorten the life of your tips. After you've cleaned the tip of the iron with your sponge, apply a small amount of solder to the tip. This is called tinning and is extremely important. The solder should flow to a 1/8" to 1/4" area of the iron. If the solder balls up on the tip and doesn't spread, then you might need to do a tip service (see sidebar) or replace the tip altogether.
• Clean is key. Before applying any flux or solder to something that is about to be soldered, you must thoroughly clean both items that are going to be soldered. You're cleaning the item of old flux or oils that might have been left over from your fingertips. To clean the item, fill a small dropper bottle with isopropyl alcohol and drop a few drops on the tip of the swab. If you don't have a dropper bottle you can dip your clean cotton tipped swab in the bottle of alcohol. With the alcohol soaked swab wipe the area that will be soldered clean.
• Flux everything. Even if you're using rosin core solder, you should flux everything when it comes to important components. After you've cleaned the item being soldered, wipe or dab a small amount of flux on the area that will be soldered. If you're soldering a wire to a circuit board, flux both the circuit board and the wire. 
• Avoid the excess. When working with a circuit board, too much solder can be a big problem. If it crosses any of the trace work, the solder can short out the component once power is applied. Trace work is the name for the etching that transfers electricity across a circuit board. Always keep your solder sucker handy. When removing a component from a circuit board, remove any remaining solder with your solder sucker. Apply heat to the solder, once melted, and suck it.
• Too Much Pressure. When working with circuit boards, the most important thing to remember is that pressure is the enemy: either pressure from pulling or tugging on a piece of wire you're trying to remove; or pressure from the iron as you press harder, trying to apply or remove something. Use a delicate touch whenever you're working with circuit boards. You may want to practice a little on something that can be destroyed to a good grip on the process. Circuit boards are pretty heat-tolerant. You can keep heat on a circuit board for 10 to 15 seconds without risk of damaging something, as long as you're aware of the amount of pressure you're exerting on the board.
Replacing a Servo Lead
In this example, we'll replace a broken servo lead. All kinds of things can cause you to break or tear a servo wire. Replacement leads are sold at most local hobby shops. But the thick 22-gauge wire and circuit board inside the servo can be a little tricky to work with. That's why we decided this would be the perfect step-by-step procedure to go over with you.
STEP 1 Remove the bottom case to your servo to expose the point on the servo circuit board where the servo lead is joined to the board. The first step is to remove the old wire. To do this, move back any rubber grommets or anything covering the solder points. Make a note of the polarity orientation before you start removing.
STEP 2 For a job like this, you should be using a very fine 1/64" or 1/32" conical tip. This is a very fine point and will allow you to apply heat to a very specific point. With the iron up to operating temperature and your solder sucker cocked and in hand, apply heat to the solder joint. 1. Once you see that the solder melts, or goes wet, trigger the solder sucker to suck away the solder on the joint. 2. After the solder is sucked away, you should be able to remove the wire easily even without any heat being applied. If you need to tug, don't! Apply heat again and slide the wire out of the through hole.
STEP 3 If solder is covering the through hole after you've solder sucked and removed the wire, then use some solder braid to pull any excess solder from the through hole. Place the braid over the hole. Apply the soldering iron above the braid. You should see the solder suck into the braid. Don't wipe the braid across the through hole; just lift up. Wiping the braid across can ruin the trace work. Repeat these last steps to all three holes.
Tip Service
How do you know when you need to replace your tip? If your iron is up to temperature and the solder balls up and doesn't spread around the tip, it's time to replace the tip or recondition your tip. Reconditioning your tip is relatively easy.
1. With the iron off, flux the tip.
2. Tightly wrap solder around the tip, but only the first half-inch of the tip.
3. Then turn on the iron and let it come up to temperature. Do this over an area where it's okay to drip hot solder. Be aware of any solder that might splash.
4. The slow heating of the tip with the solder and the flux can recondition your tip and allow it to accept solder when tinning. This tip will usually work two or three times before you must replace the tip.
Another way to fix your tip is to buy "tip tinner." It's a gray paste that's designed to repair old tips. This method works like the solder tip, and it uses an acid to adhere the new material in the paste to the tip.
SERVO LEAD Preparation
STEP 1 After you've removed all three wires and any excess solder, you must clean the board. Use a cotton-tipped swab soaked in isopropyl alcohol and dab clean the through holes.
STEP 2 Measure out the length of wire you want for the new leads. Make sure the rubber grommet is on the wire, and slide it up near the servo connecter. Cut the wire and strip back to just a 1/16" to 1/8"of insulation. Clean the exposed wire tips just in case you touched the exposed wire with your finger.
STEP 3 Using your flux swab or brush, wipe a small amount of flux over the through holes on the circuit board and over the tips of the wires.
Tips and Tricks
1. When you apply solder to your iron--or anything for that matter--if solder's popping off and flying around, something is not clean. Suck away the old solder, clean with alcohol, flux, and try it again. If solder's popping away from your iron, clean the iron and re-tin.
2. The materials used in solder and flux are harmful if inhaled directly or passively. Always work in a well-ventilated area and avoid inhaling any of the fumes or smoke released when soldering.
3. To keep your tips lasting, tin them before you turn it off. This helps to keep oxidation off of the tip.
4. If you're concerned with static electricity damaging some sensitive components, pick up a computer wrist strap. These help to prevent static electricity from damaging any components. Ground the strap to your soldering iron base station.
SERVO LEAD Installation
STEP 1 Tin each tip of wire. Just a small amount of solder is needed. Apply heat to the tip of the wire and just dab the wire tip with solder. A Panavice or some type of third hand will be needed to hold the wire while tinning. Work quickly; the wire insulation will melt if the iron is left on the wire tip too long. Don't tin the through hole or the circuit board.
STEP 2 Clean and re-tin your iron. Insert the tinned wire tip into the through hole. Apply heat at an angle so that the iron is in contact with the trace work on the circuit board and the wire at the same time. The solder on the wire should be enough to wick the board (create a seamless bond) and the wire together. If you need to apply solder, do it to the opposite side from the iron. Solder is drawn towards heat. That way the solder going towards the iron will cover everything. For this example, the solder that you tinned the wire with should be enough to get the job done. But on something like an ESC with removable wires, you might need to add a little solder.
STEP 3 Your finished joint should look like the original one, or the one shown here. If it doesn't, suck away that excess solder and redo the step. Make sure that no solder bleeds over to the other leads or any other trace work on the circuit board. After all three leads are replaced, wipe any excess flux off with a cotton-tipped swab dampened with alcohol. Give the leads a quick tug to make sure the connections are solid and you're all set. Rebuild the servo and you're ready to go. If you're not confident in your skills, practice with a standard $15 servo before replacing the leads on your $150 digital ball bearing job.
Conclusion
With this servo lead example, you'll use all your advanced soldering techniques. If you come across a job that seems even more advanced than the process described above, then maybe you should send the item to the manufacturer and let them do the repair. But, once you get proficient with this procedure, you should have all the necessary skills to tackle any RC soldering job worth doing yourself.
|
|
|
Subscribing to XRC is easy! Just fill out the form below, and you will be invoiced for $24.99 for your first year.
Offer is valid for US residents only. |
