Soldering is a process that joins together two or more items (usually metal) by melting, then putting a filler metal (solder) into the joint. The filler metal has a lower melting point than the adjoining metal, so it does not melt the work pieces.
Here, we are focused on printed circuit boards (PCBs) which contain a large number of electronic components held together on the board by solder flux which creates a strong bond between the pins of a component and their corresponding pads on the board. Providing electrical connectivity is the main purpose of this solder.
ReFlow Soldering
Currently mass-produced PCBs are mostly wave soldered or reflow soldered. Reflow soldering is generally used in a production environment where large numbers of surface mount device (SMD) components need to be soldered simultaneously on the component side of the board and do not require drilling.
The components are placed on the board with a solder flux paste that keeps the components in place until the board goes in the oven.
De-soldering
In electronics, de-soldering is a process that removes solder and components from a circuit board to troubleshoot a problem then repair or replace the problem parts. De-soldering is also used to salvage parts from a circuit board.
The various de-soldering techniques include:
- De-soldering with copper braid – commonly used to de-solder electronic components by melting the solder flux then allowing the copper braid to absorb it. This an efficient yet slow method of de-soldering components as each soldered joint requires individual attention.
- De-soldering with solder sucker – solder sucker is a small tube connected to a vacuum pump, manually-operated to remove molten flux off of pads on the PCB.
- De-soldering with Heat Gun – this is generally done to de-solder SMD components, though it can also be used for through-hole components. This process melts the solder, loosening the components, which are then removed with tweezers.
Environmental legislation in many countries and the European Community has led to changes in the formulation of both solders and fluxes. Since the 1980s, water-soluble, non-rosin-based fluxes have been on the increase as they eliminate hazardous solvents from the production environment. Those same regulations have also reduced the use of lead-based solders.
If it is not wet and shiny, then it probably is a weak, dry joint, though working with lead-free solder can produce dull surfaces even on good joints. Generally, a smooth, bright, and shiny soldered joint is a good joint.