Programmable Placement Pressure in a Placement Head for Surface Mounted Devices

Due to the broad spectrum of lead configurations of surface mount components and the variation in adhesive viscosities, various placement pressures are required. A proper adhesive meniscus must be achieved during application of components to adhesive dots to insure good lead to pad contact. This paper focuses on the development of a programmable placement pressure system which is a feature of the 4621A Omniplace Surface Mount component Placement System. A commercially available pressure regulator is programmed with a DAC to produce the required back pressure for a piston activated compliant placement spindle. Coinciding with this, the Z axis servo system drives the placement spindle to the desired Placement location. When the component, which is held by vacuum on the placement spindle, makes contact with the printed circuit board, a switch is activated. The computer receives the switch input as a signal to stop the Z axis drive. Pressure overshoot is avoided by the fast response time of the pressure regulator which controls the piston and the unique control algorithm which was developed. Included in this paper is a detailed comparison of this system for programmed placement pressure with a previous design which used load cell feedback to the computer to close the Z-Axis servo loop. It will be shown that the feed forward design is a cost saving performance enhancement. Performance enhancements directly related to this scheme include improvements in the following; reliability, repeatability of placement pressure, vacuum pressure, throughput efficiency, and spindle eccentricities.