Device and method for marking copper-clad laminates

#This invention relates to a device and a method for marking copper-clad laminates.

#Copper-clad laminates are used as a base material in the production of printed circuit boards. The latter are made from electrically high-insulating laminated materials provided with copper cladding, i.e. a copper coating. As a general rule, the intermediate layer consists of a glass-cloth laminate with a resin matrix, e.g. of epoxy resin. The intermediate layer can also be manufactured from e.g. a glass-fibre mat, an aramide fabric or fleece, or also from a phenolic paper laminate.

#A workpiece comprising a copper-clad laminate is processed in the known manner into a printed circuit by etching away parts of the copper coating so that the remaining copper surfaces form the desired conductive pattern on top of the insulating intermediate layer.

#A preferred example of an embodiment will be explained in more detail below with reference to the drawings, in which

#FIG. 1 shows a diagrammatic representation of the optical components of a marking device according to the invention;

#FIG. 2 shows a diagrammatic side view of a marking device with the components of FIG. 1;

#FIG. 1 illustrates the optical construction of the device according to the invention for marking copper-clad laminates. A laser 10 comprises a resonator 12 with a completely reflecting mirror 14 and a partially penetrable mirror 16, through which the laser beam 18 generated in resonator 12 is emitted. Resonator 12 accommodates the active medium 20, in this case an Nd:YAG crystal, which is stimulated in a manner not shown in more detail, e.g. by flash tubes, to initiate the laser process. Resonator 12 also comprises an audio-optical modulator 22, which enables laser 10 to be operated in a pulsed manner. Between active medium 20 and audio-optical modulator 22 there is a screen 24, with which part of the intensity reflected between mirrors 14,16 can be screened. Thus the intensity of laser beam 18 can be controlled by either enlarging or reducing the opening of screen 24. It is also possible to control the intensity by controlling the pulse frequency of the audio-optical modulator 22 or by altering the lamp current of the flash tubes.

#The laser beam 18 emitted by laser 10 is directed onto a diverging lens 26, which expands beam 18. The expanded conical beam 28 then impacts on a convergent lens 30, which focuses the laser beam at a focal point f on the surface of the diagrammatically represented workpiece 32.

#Diverging lens 26 and convergent lens 30 basically form a telescope. By expanding and then focusing beam 18 through the telescope it is possible to obtain a very small focus, f, so that the surface intensity on the surface of workpiece 32 is very high. Where the focal distance of convergent lens 30 is 240 mm, an expansion of about factor 6 gives a focus diameter of less than 50 m, for example. Intensities as high as this make it possible to mark copper-clad laminates in line with the principles explained below in connection with FIGS. 5 and 6.