Fundamental Analyses of Smart Tooling for Assembly of Thin Flexible Circuit and Board Systems

Abstract

Flexible nature of flexible circuits/boards poses new fixture tooling challenges for standard surface mount assembly equipment. The flexible substrates experience significant transverse displacements under perpendicular assembly forces during solder paste printing and component placement processes. The displacements result in misregistration of the component leads and substrate bond pads, leading to assembly process defects. Solder reflow process further complicates the issue due to the thermo-mechanical warpage induced. Reengineered and specialized dedicated tooling for fixturing flexible substrates in standard assembly equipment is becoming extremely important. This paper focuses on developing analysis methodologies and theories for implementing Smart Tooling. The primary goals being to determine the impact of fixturing on assembly process quality and to determine optimum fixturing configurations for thin flexible circuit board assemblies based on circuit board design data. A mathematical model to describe both transverse and perpendicular displacements of flex substrates is developed, and its close-form solution for transverse displacements is obtained. Using a “near” optimum fixturing configuration to minimize transverse displacements is verified.