Selection of IR detectors for a fast laser soldering process with simultaneous solder joint qualification

High effort is required for quality assurance after mass soldering of electronic devices. In contrast to that, a laser soldering process with an on-line quality control system is well-suited to the production of interconnections with high reliability. This contribution presents a new principle of closed loop control and a solder joint qualification method based directly on the recognition of wetting. In this way, shorter soldering cycles can be achieved compared to other systems. From thermal analysis of laser soldering processes it is known that wetting is related to a significant rise of the heat flow inside the solder joint leading to a characteristic change of the heat radiation which is detectable with an infrared detector. The selection of an infrared detector, the infrared measuring system and its application in a laser soldering system is described. The influences of thermal qualities of the solder joint and solder paste on the slope of the detector signal are discussed. The operating principle of the quality control algorithm is demonstrated at the soldering of 1812 and MELF0204 package components onto a 35-μm copper-plated printed wiring board (PWB)