Use a fixed power soldering iron, 25-watt for small jobs and 100-watt for larger jobs with heavy cabling. [1] X Research source If possible, variable temperature irons are available, which will make for the safest treatment of the boards. The tip temperature can be controlled to suit the size of the job.
Solder that is 60/40 becomes pliable at 361 °F (183 °C) but doesn’t melt until it’s 370 °F (188 °C), which means it may be difficult to work with if you’re a beginner. Instead you can try solder that’s 63/37 since it melts at 361 °F (183 °C). Various lead-free alloys are becoming necessary in recent years under the RoHS regulatory initiative. These require higher soldering temperatures and do not “wet” as well as tin-lead alloys. While they are safer, they are also more confusing. The most common is 96. 5% tin to 3. 5% silver and will produce a joint with less electrical resistance than a tin-lead alloy. In practice, this is not a reason to use it; the safety issue is the driving factor. You can also get solder that is almost 100% tin, but it is more expensive. Both lead and lead-free formulations are available online at places like solderdirect. com and in various stores in most localities.
There are several different fluxes commonly available for electrical/electronic work. In order of popularity, these are RMA, RA, and water-soluble fluxes. [3] X Research source The more active a flux is, the more important it is that it not remain after soldering, lest continuing chemical action compromise or damage the operation of the electrical or electronic equipment. In particular, water-soluble fluxes must be removed. After soldering, rosins leave a brown, sticky residue which is ideally, non-corrosive and non-conductive. Cleaning can be accomplished with a purpose-formulated rosin removal product, or with isopropyl alcohol. No-clean flux leaves a clear residue after soldering, which is non-corrosive and non-conductive. This flux is designed to be left on the solder joint and surrounding areas. Water-soluble flux usually has a higher activity that leaves a residue which must be cleaned with water. The residue is corrosive and may also damage the board or components if not cleaned correctly after use.
Soldering other electrical items, such as wires or lugs, has slightly different techniques, but the general principles of operating the solder and iron are the same. Note however, the lugs and other unsupported soldering points require a firm mechanical connection prior to soldering. A solder joint does NOT provide mechanical strength or resistance to vibration; it only provides a very low resistance electrical connection.
Some kind of clamp or stand is usually best to hold the board in place while you solder the components.
Leave 7–12 inches (18–30 cm) of space between the electronic components and your face, or solder bits or hot flux may reach your eyes. Safety spectacles are a very sensible precaution. Molten solder may splatter, and is essentially unpredictable.
Carefully place the tip (with the blob) onto the interface of the lead and pad. The tip or blob must touch both the lead and the pad. The tip of the soldering iron should not be touching the nonmetallic area of the PCB, whether fibreglass (very common) or some other material. This area can be damaged by excessive heat.
If the solder does not melt onto the area, the most likely cause is insufficient heat has been transferred to it, or the surface needs to be cleaned of grease or dirt. The activity of the flux was not sufficient, and external flux may be necessary. Careful cleaning of surfaces prior to soldering may be needed. Use care—sandpaper will generally be too harsh and steel wool (though less mechanically harsh) will add tiny bits of conductive metal—probably leading to unintended shorts and electrical misbehavior.
On plated-PCBs, you should stop feeding when a solid concave fillet can be seen around the joint. On non-plated PCBs, you want to stop feeding when the solder forms a flat fillet. Too much solder will form a bulbous joint with a convex shape (ie, blob-like), while too little solder will form an irregular concave joint. Both are visual indications that the solder joint is defective.
Try to err on the side of irons that are less powerful than you think you might need. A 30-watt iron will be adequate for most electronic work. Practice soldering is a very good idea. If working with a double-sided circuit board check both sides for good solder joints. A good joint will look shiny and cone-shaped. if it looks frosty and dull then it is likely a cold joint. [5] X Research source
The solder joint should coat the surface of the component evenly, not too much such that it forms a glob, nor too little such that it does not completely coat the surface.
Clean the iron in between each component that you solder. Use a damp sponge or bronze (or brass) wool to clean it thoroughly. [6] X Research source
If the components are too hot to handle, use needle nose pliers, or a tool called helping hands which consists of two alligator clips attached to a little articulated stand. If you watch carefully, the cooling solder will settle right before your eyes.
Nobody is perfect, not even the professionals. Don’t be ashamed to repeat a bit of soldering work (it’s officially called rework in the business). It will save you time in troubleshooting later.
