Very Little has been written in the general audiophile press on the subject of soldering. This is unfortunate, as many of us are required to perform the task from time to time, and should know how it is done. Like anything else, there is a right way and a wrong way to go about it. Since a poor solder joint can do much to undermine the quality of the signal attempting to pass through it, it is important to insure quality whenever we tackle a soldering job. I hope that this brief introduction will give you the information you need to make minor repairs or modifications. Or, in the case of the more ambitious hobbyist, become proficient at making ultra-high quality solder connections for more involved projects.
The object in soldering is to join two metal conductors by flowing molten metal across their surfaces. Sounds easier than it really is. In a proper joint, the solder molecules actually combine with those in the metals being joined. The term applied to this action is wetting.
Proper technique requires proper tools, and this begins with a good quality iron of the right temperature for the job. Fixed temperature irons come in various sizes or wattage's and cost between $15.00 and $50.00, depending on quality. Fixed wattage irons are the most common types, although variable heat devices are the choice of most professionals. These units allow the user to select a variety of temperatures, one that will be correct for the task at hand. Expect to pay $50 and up for a variable iron.
The next most important element of the equation is the solder itself. For audiophile quality work this will normally be a solder containing a small percentage of silver. Most all solders contain a small inner core of flux. Flux helps the solder adhere to the work by removing oxides from the surfaces of the metals. For electronics application, only resin core solder should be used.
To begin, be sure that the metal surfaces of the work are clean, free of oils and debris that could reduce the ability of the solder to adhere. Also be certain that the tip of the soldering iron is clean and properly tinned. Place the tip of the iron at the junction of the two pieces being joined, this will insure that even heat is applied to both. After the metal has been sufficiently heated, apply the solder at the junction of the two pieces. Do not apply solder to the tip of the iron itself. The solder will flow to the hottest part of the connection, the point of iron contact. Withdraw the iron as soon as possible and let the joint cool. It is important to heat the connection for as little time as possible to avoid undue stress to the conductor and/or insulation or dielectric. Avoid disturbing the completed joint during cool-down. Finally, de-flux the area with an appropriate solution to remove unwanted traces of the resin flux. Your labor should have resulted in a bright, shiny, smooth surface.
A dull, rough or grainy surface texture is indicative of a solder job gone wrong, a cold solder joint has been produced, and is unacceptable. Either too little heat was used or too rapid cooling has occurred. Reheat the joint to see if you can restore the connection. If that fails, remove the old solder and start over.
Certain more specialized jobs, such as soldering components on a printed circuit (PC) board, require additional knowledge and care. The component parts themselves (especially sensitive transistors and integrated circuits) can easily be damaged with excessive heat. When installing these sensitive parts, one must be sure that an iron of the proper heat (wattage) has been selected. Small heat sinks designed especially for the job (or alligator clips) may be attached to the parts themselves to help dissipate damaging heat.
If you need to repair a poor solder joint, or replace a component soldered to a PC board, you must first remove the old solder. This may be accomplished using a variety of methods. Solder removal wick or braid is the most common. This product consists of resin coated copper that attracts molten solder. After the old joint has been reheated, the wick is applied to draw the solder off the connection. This procedure requires a bit of practice to master. Another common means of removing solder employs a tool affectionately known as the "solder-sucker." This little device consists of a spring loaded plunger inside a tube. Pressure on the trigger releases the plunger, creating a suction or vacuum at the tip. Simply heat the connection, melt the solder, put your "solder-sucker" in place and viola, clean surface! Concerning costs, a roll of solder wick sells for a few Dollars, the vacuum tool commonly sells for about ten.
It takes practice to produce a good solder joint. I recommend that you spend some time honing your skills before attempting more important work.
Dr. A.J. van den Hul has put together what he calls "The Commandments for Optimal Soldering. " While these recommendations were originally targeted for implementation with van den Hul products, the general guidelines put forth aptly apply is most cases. Although some of the suggestions are a bit esoteric for the average hobbyist, much can be learned from the basic techniques. It may also help you to understand some of the reasons behind the high termination costs of some of the more exotic, difficult to work interconnects and speaker cables. What follows is an amended version of those recommendations.
CARE AND FEEDING OF THE SOLDERING DEVICE -
I hope that the information we have provided here will further your understanding of the soldering process. Good luck, and don't burn your fingers!