NON-CONTACT TEMPERATURE MEASUREMENT IN SM COMPONENT REWORK

Abstract

Although surface mount assembly equipment has been rapidly developed during the last decade, surface mount device rework equipment is still largely basic and its development has not kept pace. The rework process is still viewed as a side issue, even when manufacturers consider the quality of the reworked board to be as good as the original board. An important consideration in rework is the control of the heating of the surface mount (SM) component, and although various attempts have been made to automate the heating process, the rework heating process is unfortunately still not as good and uniform as those for conventional SM reflow. Primarily, the techniques used for rework are manually assisted, and usually rely on the rework operator's judgement in the observation and control of the rework process. A real-time closed-loop controlled rework-reflow system, capable of reflowing all SM components regardless of their heat capacity, type of Printed Circuit Board Assembly (PCBA) and the position of components on PCBA, has been developed as part of a fully automated robotic rework cell. The reworkreflow system is a separate unit, which can be easily adapted for use in any manual rework system. An important part of the system is a non-contact sensor, for real-time measurement of the reflow temperature and its feedback to the device controller unit. The paper describes the closed-loop controlled reflow system employed in the automated robotic rework cell, highlights the problems associated with its use, and then summarizes the requirements for non-contact temperature measurement in reworking SM components. The principles of non-contact measurement and the importance of emissivity for temperature measurement are also highlighted, and the experimental results of the true emissivity of the SM components are presented.