53 - Production Engineering and Reliability

Abstract

This chapter discusses production engineering and reliability. The introduction of printed circuit boards made it possible to solder all the inserted components on to the pcb at once, instead of having to solder each component to terminals one by one with the aid of a soldering iron. Components for automatic mounting are generally axial or radial in shape but following recent developments, other types of components also can be mounted automatically. An automatic insertion of axial and radial components, which usually constitute 65–75 per cent of the total number of components on a printed circuit board, has become very common as the necessary machines have become widely available. Flux coating is first necessary to remove any oxides from the surface of lead wires of components and the copper foil of the pcbs and then to coat them with flux to improve their ability to take solder. It is important to keep the density of the flux constant in a specific gravity range of 0.82–0.86. Equipment has been developed to coat flux which can control specific gravity automatically. A pump, a chamber, and a jet nozzle are provided in the soldering bath. The pump is driven to jet the solder, the width of the jet being determined by the size of the pcbs. In a wave variant, the solder is jetted into waves. This method is also known as hollow wave. Dual waves are opposed to each other to jet the solder.