Solder advisor—knowledge-based solder paste selection system

The use of surface mount technology (SMT) in printed circuit board (PCB) assembly has increased substantially in the last decade. During this time, surface mount components have been characterized by decreasing component lead pitch, and increasing component packing density and lead counts. These factors have increased the complexity associated with the assembly of fine pitch surface mount PCBs. Solder paste is a prime factor in the determination of process efficiency and manufacturing yield in the PCB assembly domain. The selection of a solder paste is driven primarily by product design, manufacturing parameters, and the inherent properties of the solder. These criteria are interrelated in a complex manner such that the cause and effect relationships among them are not always apparent. In addition, factors such as the depletion of the ozone layer in the atmosphere and the associated environmental concerns have resulted in restrictions being placed on the use of chlorofluorocarbon (CFC) solvents to clean post-reflow solder paste residue. Therefore, solder paste selection is a multi-attribute problem that requires substantial domain knowledge and technical expertise. This paper describes the design and development of an expert system for solder paste selection for surface mount PCBs. The system mimics the thought process of solder paste experts. It formalizes the complicated set of procedures used by an expert in selecting a solder paste and makes the solder paste selection expertise available to a wide range of people. PROLOG—a versatile language for developing expert systems—was used to develop this user-friendly personal computer based expert system.