In the THT, components are mounted on a contract manufacturing services by inserting component leads through holes in the board. They are then soldering the leads in place on the opposite side of the board. ECM companies do not brand their components in any way at all; instead the components remain un-branded and gain the name of the OEM Company that offered out the contract. In the SMT, components are added to a PCB by soldering component leads or terminals to the top surface of the board.
IBM started a trend by outsourcing certain jobs, they classed this as outside core competence and this in turn sparked a trend of contracts being outsourced which gave ECM companies a method of increasing economies of scale. In time the market power shifted from OEMs to larger ECMs, this was largely in part too many OEMs selling off all of their old production units to Electronic Contract Manufacturers. They can get the bare printed circuit boards required along with all of the other necessary parts. Specialists will not only assemble the PCB but will also conduct any necessary testing to make sure everything is working correctly. Tin-Lead soldering has been the basis for interconnections since the beginning of the use of led circuit board, and all associated materials and processes have been developed with the use of that material in mind.
If you already have all of the components necessary to create your PCB, a PCB manufacturing specialist can simply put them together and create the finished product. If your next project demands a custom-created circuit board fabrication (PCB), you may not be in a position to create one on-site due to facility, equipment or staffing limitations. Now that there are circuits on each side of the board, the components are connected via a series of strategically placed through-holes which allow for an unimpeded electrical connection between the two.