Soldering
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Soldering is a method of applying a metal of lower melting point to join other metal parts using solder. Soldering can be performed in a number of ways, including bulk liquification, or by using a point source such as an electric soldering iron or brazing torch.
One application of soldering is making connections between electronic parts and printed circuit boards, another is in plumbing.
Soldering is distinct from welding in that the base materials to be joined are not melted. The lower melting point solder can be melted away leaving the original materials intact.
Basic electronic soldering techniques
All solder pads and device terminals must be clean for good wetting. The soldering iron or gun must be clean, otherwise components may heat up excessively. The devices must be mounted on the circuit board properly. One technique is to elevate the components from the board surface (a few millimeters) to prevent heating of circuit board. After device insertion, the excess leads can be cut leaving only a length equal to the radius of the pad. You may use plastic mounting clips or holders for large devices to reduce mounting stresses.
Heat sink the leads of sensitive devices to prevent heat damage. Apply soldering iron or gun to both terminal lead and copper pad to equally heat both. Apply solder to both lead and pad but never directly to the tip of soldering iron or gun. Direct contact will cause the molten solder to flow over the gun and not over the joint. The moment the solder melts and begins to flow, remove the solder supply immediately. Do not remove the iron yet. The remaining solder will then flow over the junction of the lead and pad, assuming both are free of dirt.Let the iron heat the molten solder for a few seconds. This will let the excess flux vaporize. Remove the iron from the junction and let the junction cool.
Be sure not move the joint while it is cooling. Doing so will result in a fractured joint. Do not blow air onto the joint while it is cooling. Instead, let it cool naturally. A good solder joint is smooth and shiny. The lead outline should be clearly visible.Clean the soldering iron tip before you begin on a new joint. It is absolutely important that the iron tip be free of residual flux and solder. After you finish all of the joints, remove excess flux residue from the board using alcohol, acetone, or other organic solvent.
Soldering defects
Soldering defects are solder joints that are not soldered correctly. These defects may arise when solder temperature is too low. When the solder is too cold, it will not flow and will "ball up". An incorrect solder type (for example, electronics solder for mechanical joints or vice versa) may lead to weak joint. An incorrect or missing flux can corrode the metals in the joint. Without flux the joint may not be clean. A dirty or contaminated joint usually leads to a weak bond. A lack of solder on a joint will make the joint prone to failure. An excess of solder can create "solder bridges" which create short circuits. Movement of metals being soldered before the solder has cooled will make the solder appear grainy and may occur as a weakened joint.
Soldering defects in elecronics can lead to short circuits, high resistance in the joint, intermittent connections, components overheating, and damaged circuit boards. In mechanical joints defects can lead to joint failure and corrosion.
See also
de:Löten eo:lutado nl:Solderen
