7.1 What is Image Transfer?

Image transfer basically involves the transfer of the conductor pattern from the film master on to the copper clad base material or any other metal clad laminate. In the fabrication of the PCB, the two methods common for image transfer are:

• Photo printing method; and

• Screen printing method.

  • Photo Printing: This is an extremely accurate process, which is generally applied to the fabrication of semiconductors and integrated circuits wherein the conductor widths are typically in the region of a few microns. Although such a precision technique is not required in the production of general purpose PCBs, yet where conductor widths of 100 ?m are required and for PCBs for professional applications, the photo printing process is resorted to.

  • Screen Printing: Although less precise than the photo printing process, screen printing is a comparatively cheap and simple method. The majority of PCBs produced worldwide are screen printed.

7.2 Laminate Surface Preparation

Copper surface plays a major role in the success or yield of the image transfer process. It demands that the surface should be carefully inspected for pits, drilling burns and any other types of irregularities. If unacceptable defects are observed, the image transfer process should not be carried out further and the defective material should be rejected straightaway. So, for the image transfer to take place, the cleaning of the copper surface prior to resist application is an essential step for any type of PCB process. The difficulties most often encountered in PCB fabrication...