Non-contact printing means to print with flexible Screen template between the space of PCB and template in the PCB printing craft. Next, the PCBA production technician will teach you the principle and process of non-contact printing.
Placing the PCB on the table support before printing,fixing it by vacuum or mechanical method,and to make the printed graphics window processed wire mesh be tightened on a metal frame and aligned with the PCB.There is a distance between the top of the PCB and the bottom of the screen(it usually called scraping dynamic clearance)At the beginning of printing, the solder paste is placed on the screen in advance. The scraper moves from one end of the screen to the other end and presses the screen to make it contact with the PCB surface.At the same time, the solder paste is pressed and scraped to leak and deposit on the solder pad of the PCB through the graphic window on the screen.
Solder paste and other printed pastes are all fluid, and the printing process follows the principles of fluid mechanics.Screen printing has three features:The solder paste in front of the scraper rolls in the forward direction of the auxiliary blade;screen and PCB surface are separated by a short distance;the solder paste is transferred from the mesh to the PCB surface during the process of wire mesh contacting to disconnecting the PCB surface.
Be sure to set the route of print head when usage,to keep a certain distance from edge of diagram,or it will cause deformation or irregular of the edge printing due to too short route. Too small pressure of the print head solder paste so that the solder paste can not effectively reach the bottom of the template hole and not be well deposited on the solder plate, may also make the screen can not touch the PCB and affect the printing effect;too much printing pressure will make the secondary tool deformation or even scrape the solder paste on the larger hole of template , forming a concave surface solder deposit, damaging to the template seriously.The suitable method is first to use certain pressure to obtain a thin and uniform layer of solder paste,then increase pressure gradually so that the solder paste all evenly scraped for each time of printing operation.
Non-touch printing is printed in extreme simple structure, solder paste is printed onto PCB solder pad when the auxiliary tool disconnects from PCB through template. The disadvantages of non-touch printing is becoming obvious as the improvement of mounting density requirement and the generation of fine pitch printing requirements
