Analysis of alternative rework strategies for printed wiring assembly manufacturing systems : Morris Driels and Major John S. Klegka. IEEE Trans. Compon. Hybrids mfg Technol.14(3), 637 (1991)

Abstract

This paper presents a model for predicting the cost of test, diagnosis, and rework activities in the manufacture of printed wiring assemblies (PWA's). Rework is defined as all actions taken to correct or improve the basic assembly process. These actions may include those of inspectors and solder touchup technicians who do not add value to the PWA, but whose actions are required in order to produce acceptable yields from the manufacturing process. Two alternative rework strategies for contemporary PWA manufacturing systems are presented: terminal rework and distributed rework. Rework may occur after all assembly operations have been accomplished (terminal rework) or it may be distributed throughout the assembly process. This paper allalyzes the economic basis for deciding between the two rework strategies. The paper assumes that the only reason for utilizing distributed rework is to reduce the cost of producing acceptable PWA's, otherwise the cost of the distributed rework effort cannot be justified. The paper presents a model of each rework strategy. The effect of each strategy upon first pass yield (FPY) of the manufacturing process is discussed. The effect on FPY is then used to evaluate the economic benefit of each rework strategy as an aid in deciding which strategy to use. The increase in FPY needed to justify distributed rework is calculated. I. PWA MANUFACTURING SYSTEMS WIDE variety of printed wiring assembly (PWA) manA ufacturing systems may be observed throughout the industry. These systems have been developed to operate efficiently in specific areas of the PWA manufacturing environment as determined by factors such as technology, production volume, design complexity, component types, and product life span. In the area of surface mount technology (SMT), for example, considerable standardization has been achieved in interconnect methods, component shapes and packaging, and substrate design. As a result, a wide variety of SMT products are manufactured using very similar assembly systems. In order to accurately predict the costs associated with operating these systems, they must be modeled on a detailed basis. To obtain the needed detail, models have been developed in which the total system is decomposed into individual modules. The individual modules are analyzed to model the cost and performance of each station [l], [2 ] . Manuscript received May 14, 1990; revised April 10, 1991. M. Driels is with the Department of Mechanical Engineering, Naval Major J. S. Klegka is with the Department of Civil and Mechanical IEEE Log Number 9101464. Postgraduate School, Monterey, CA 93943. Engineering, United States Military Academy, West Point, NY 10996. Ill 11111 I11111 I lllllllllllrl 631 A PWA manufacturing system usually consists of a series of automated and manual assembly and process stations. The stations may be connected by an automatic or manual transfer device which moves the partially completed PWA's through the system. Each PWA follows a relatively fixed path through the manufacturing system. A typical assembly system consists of a solder paste dispenser, one or more automatic component placement machines, one or more manual inspection and placement stations, a solder reflow station, a cleaning station, and a test, diagnosis, and rework station [8], [9],