SMT FEEDER SLOT ASSIGNMENT FOR PREDETERMINED COMPONENT PLACEMENT PATHS

Surface Mount Technology (SMT) is a popular method of Printed Circuit Board (PCB) assembly in which high speed automated assembly machines a re capable of placing in excess of 40,000 components per hour. In orde r to achieve these impressive assembly rates, complex placement machin es must be programmed efficiently. Intrinsic to the configuration of t hese machines and the assembly process are some well established Opera tions Research problems. This paper addresses the feeder sequencing pr oblem for an assembly machine with a sliding feeder rack in conjunctio n with a X-Y positioning table and a turret placement mechanism. This problem is a Quadratic Assignment Problem, and is proven to be NP-comp lete.(1) Two different heuristic methods are proposed, each with uniqu e characteristics that have the potential to be beneficial to an assem bly operation dependent upon the restrictions of the planning task. On e method is to assign feeder slots based on the transition between com ponent types that naturally occur in the board placement path. The sec ond method begins with an initial slot assignment and identifies excha nges between pairs of slots that generate improvements in the objectiv e function. Minimizing the feeder travel distance over an assembly is the goal of each heuristic. A comparative analysis between the two heu ristics is performed. Examples are presented and the attributes of eac h method are discussed. Arguments are presented to support ''near-opti mal'' solutions to the problem. Given the complexities of the system, proper planning of the assembly process can take advantage of the inde pendent control of each mechanism to create a natural relaxation of sp ecific constraints.