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Control of the Infrared Reflow (IR) soldering process requires the understanding and regulation of several complex variables. The key to the successful use Surface Mount Technology (SMT) lies in understanding how the various process control parameters affect the overall reflow operations. When a variety of components are soldered on to a Printed Circuit Board (PCB) simultaneously in the IR oven using the reflow soldering mechanism, the process control variables that need to be considered include the melting point of solder paste, the size, type, and quantity of components placed on the PCB, the mass and the thermal area of the workpiece, and conveyor speed. A prerequisite to the achievement of high process yields is the identification of the optimal temperature profile and the range between which the profile is acceptable. This information is subsequently used to arrive at the relevant IR oven settings required. The in-depth process knowledge required to study the process variables and deduce IR profiles is not commonly available.

A knowledge based or an expert system approach was used in this research to help with IR profile identification. The system developed considers the major process control parameters and the interrelationships among them to deduce the optimal temperature profile and a range between which the profile is considered 'acceptable'. The knowledge based IR profile identification expert system was developed using PROLOG on a personal computer. Results are displayed using a combination of graphical and textual output. The system was designed to function in a stand alone capacity. The IR profile identification expert system's architecture integrates inference mechanisms with the knowledge (facts and rules) provided by the domain expert. It allows the user to update or delete the facts and rules stored in the knowledge base. Consequently, it provides an avenue to enhance the capacity of the system to incorporate domain specific changes.


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