 In soldering, an alloy of tin and lead, or later bismuth and tin, is melted and adheres to other, nonmolten metals, such as copper or tinned steel.Solder makes a strong electrical and mechanical connection.Point-to-point wiring is not suitable for automated assembly (though see wire wrap, a similar method that is) and is carried out manually, making it both more expensive and more susceptible to wiring errors than PCBs, as connections are determined by the person doing assembly rather than by an etched circuit board.