Masters Abstracts (1996)

VENKATESWARAN, SUNDARAM
(September 1996), American Airlines, Dallas, TX

Email: sundaram_venkateswaran@amrcorp.com

Comprehensive Process Control for Solder Paste Stencil Printing

The goal of stencil Printing solder paste in surface mount Printed Wiring Board (PWB) assembly is to apply an accurate and repeatable volume of solder paste at precise locations. The causes for a substantial proportion of the problems associated with PCB assembly can be traced back to the solder paste printing process. Some stencil printing related problems include depositing the correct volumes of solder paste, ensuring that the stencil is registered at the appropriate position with respect to the PCB, and understanding the effects and interrelationship of the process parameters. This can be achieved through extensive experimentation and with a thorough understanding of the process.

Process control in stencil printing has become significantly more important over the years due to the introduction of fine pitch and ultra fine pitch technologies. It is particularly difficult to control a stencil printing process which consists of a mix of components with various lead pitches. Three important issues have to be considered in the stencil printing process to obtain a good yield. They are (i) setting up the process in an efficient way, (ii) monitoring and controlling the process when necessary and (iii) troubleshooting the process when a defect occurs. This research focused on the design and development of software systems that could perform the above-mentioned functions.

Three systems were developed in this research. They are the process advisor, the intelligent control system (or the ICS) and the diagnosis system. The process advisor (the first system) provides for the setup of the stencil printing process. The ICS (the second system) was developed to control the stencil printing process. Statistical control techniques have been applied to determine the quality of the print process. A unique fuzzy control and topology mapping algorithm is used to exercise control over the process. The diagnosis system (the third system) is used to troubleshoot the process when the ICS is unable to control the printing process.