10.1 Need for Mechanical Operations

The PCB fabrication process involves a number of mechanical operations to prepare the circuit boards for the chemical processes of image transfer, plating, and etching. The process starts with the acquisition of laminate sheets which may be as big as 2 m 2 m or bigger. Therefore, the mechanical process such as cutting to size, drilling holes and shaping play an important role in the final quality of the printed circuit board.

Unlike other PCB processing steps, most of the mechanical operations require considerable manual handling of the board. Such operations do not form part of the transfer-line equipment, and would therefore, have a major impact on the costing of the final product.

Each mechanical operation has its own set of requirements in terms of tolerance and accuracy. In general, tolerances should be made as narrow as they are functionally really needed. Proper choice of tools and their sharpness are very important in each of the mechanical operations for obtaining an acceptable machining finish. Blunt and dull tools result in chipping because of resin brirtleness of the laminate. Proper application of machining forces must be kept low. Excessive machining forces may cause partial de-lamination because of the inherent laminate structure, thereby weakening the interlaminar bond strength. A good knowledge of the base material composition, equipment and tools complemented with good operator habits can facilitate good mechanical operations resulting in higher quality PCB yield.

10.2 Cutting Methods