A soldered joint which is improperly made will be unreliable and is likely to get worse in time. It may not have made any electrical connection at all, or could work initially and then cause the equipment to fail at a later date! It can be hard to judge the quality of a solder joint purely by appearances, because you cannot say how the joint actually formed on the inside, but by following the guidelines there is no reason why you should not obtain perfect results.
A joint which is poorly formed is often called a "dry joint". Usually it results from dirt or grease preventing the solder from melting onto the parts properly, and is often noticeable because of the tendency of the solder not to "spread" but to form beads or globules instead, perhaps partially. Alternatively, if it seems to take an inordinately long time for the solder to spread, this is another sign of possible dirt and that the joint may potentially be a dry one.
There will undoubtedly come a time when you need to remove the solder from a joint: possibly to replace a faulty component or fix a dry joint. The usual way is to use a de-soldering pump or a de-soldering station (More demanding users using CMOS devices might need a pump or station which is ESD safe).
Sometimes, it's effective to actually add more solder and then de-solder the whole lot with a pump or de-soldering station, if the solder is particularly awkward to remove. Care is needed, though, to ensure that the boards and parts are not damaged by excessive heat; the pumps themselves have a P.T.F.E. nozzle which is heat proof but may need replacing occasionally. De-Soldering stations are a must when de-soldering advance or multilayer boards. .
For home user or service engineer an excellent alternative to a pump is to use de-soldering braid, also known as Solder-Wick. The TW No clean braid is a specially treated fine copper solder braid which draws molten solder up into the braid where it solidifies.
The best way to use solder braid is to use the tip of the hot iron to press a short length of braid down onto the joint to be de-soldered. The iron will subsequently melt the solder, which will be drawn up into the braid. Take extreme care to ensure that you don't allow the solder to cool with the braid adhering to the work, or you run the risk of damaging p.c.b. copper tracks when you attempt to pull the braid off the joint.
