TWO INDEPENDENT X-Y TABLES CONCEPT FOR SIMULTANEOUS SCREEN PRINTING
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2001-Dec-11
An automated Surface Mount Component Assembly factory is required to populate two separate double sided boards. With different radio models, the total possible combinations of the two boards are 8 (4 RF x 2 CONTROLLER). The factory needs to oper- ate at a 35.0 second frequency; on batch sizes of one with no additional time loss for set-ups and change- overs. Processing PCBs involves screen printing of solder paste as one of the very first steps. Therefore, a screen printer is required to print one board, change the screen, print the second board, and finally change the screen again for a new board; all of this to be accomplished in 35.0 seconds. Current screen printers are limited in flexibility in that automatic screen change and wash are not available, particularly for a multitude of screens. Manufacturers have agreed to develop this sophisticated printer. The cycle time, however, for an automatic screen change, and wash was estimated at 120 sets. Utilizing a total of four screen printers (2 top + 2 bottom) that this factory can operate on batch sizes of four within the 35.0 second cycle time. constraint. This publication describes a method that reduces the number of machines to half by combining the task of two printers into one, resulting in a 40% cost reduction along with a reduced floor space mquirement. Also, the factory performance can he improved to a batch size of troller boards can also be placed together on one nest with tooling pins alignment and be treated as one board. The vision system will only look at one fiducial per board and perform a best fit alignment to the screen which now has art works for both boards. This alignment greatly depends on the tolerance between art work and tooling holes on the PCB, which is min z.005" and max *.OlO" when two boards are combined on one nest. These tolerance stack-ups may result in inaccurate registration of screen to PCBs.