Method for drilling multilayer printed circuit boards
BACKGROUND OF THE INVENTION 
     The invention is directed to a method for drilling multilayer printed circuit boards with a printed circuit board drill having spindles which are stationary relative to one another, and is also directed to a printed circuit board drill for the implementation of the method. 
     Previously known printed circuit board drills are not in position to simultaneously drill a plurality of printed circuit boards individually according to the different interior layer distortions. For this reason, multi-spindle drills can only be employed in single-spindle fashion. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to specify a method and to create an arrangement with which the drilling of multi-layered printed circuit boards is permitted in a more rational fashion than was hitherto possible. 
     In order to achieve this object, one proceeds according to the invention such that the individual receptacle plates of the printed circuit board drill are adjustable in two coordinate directions. The offset of the interior layers of a multi-layer printed circuit board relative to the rated position is identified on the basis of a rated-actual value comparison. The respective receptacle plate is readjusted to the prescribed rated value depending on the size and direction of the interior layer offset of the printed circuit board. 
     The identification and evaluation of the interior layer offset as well as the re-adjustment of the receptacle plate can occur with a computer. 
     The printed circuit board for the implementation of the method is designed such that the drill is equipped with a plurality of drill spindles arranged side-by-side and stationary relative to one another, and such that every drill spindle has a receptacle plate allocated to it, and wherein the receptacle plates are adjustable independently of one another. 
     These measures enable the simultaneous setting of a plurality of different offset values at one machine, so that multi-spindle drills can be employed as a result thereof. A plurality of printed circuit boards can thus be simultaneously drilled, so that the required area for the drill is reduced and the costs arising are lowered. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a stationary seating plate in a known, single-spindle drill having an identified position of the interior layer pads; 
     FIG. 2 is a supporting table of the invention having three adjustable receptacle plates for one multilayer printed circuit board each, and having three drill spindles; 
     FIG. 3 is a cross section through a printed circuit board at the test drill patterns; 
     FIG. 4 is an individual test drill pattern in plan view; and 
     FIG. 5 is an arrangement of the test drill patterns at the active grid field. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a seating plate 5 as well as an offset of the drill pattern in an X-direction and a Y-direction with a printed circuit board 18 seated thereon. Without changing the drill spindle (not shown) above the seating plate 5 on which a multilayer printed circuit board -8 is situated, the bore 2 would occur eccentrically relative to the interior layer pad 1, and would thus produce an unusable multilayer printed circuit board. According to a method to be set forth later, however, the offset of the interior layers relative to the rated value is identified, and an adjustment of the individual seating plate is undertaken in the direction of the arrow 3 until the drill is situated in the center of the interior layer pad The drilling event can be subsequently undertaken. The bore 4 represents a fitting bore for the printed circuit board 18 and for the seating plate 5. 
     FIG. 2 shows the supporting table 19 on which three receptacle plates 5 are situated, and on which the printed circuit boards 18 are arranged in turn. Reference numeral again represents an interior pad, 2 represents the position of the drill spindles relative to the position of the interior pad, and 3 represents the adjustment value of the receptacle plates. As may be seen from this figure, the advantage of the method of the invention is that the three receptacle plates can be adjusted independently of one another, so that drills having a plurality of drill spindles can now be employed, whereby the drill spindles of these machines are arranged in non-movable fashion relative to one another. 
     FIG. 3 shows a portion of a cross section through a printed circuit board. What are referred to as test drill patterns 6 and 7 are thereby situated at the edge of the printed circuit board. These test patterns are applied as interior layers of the multilayer printed circuit board 18 along with the signal layers 13 also provided as interior layers. Potential layers 14 are also provided as interior layers. The quadratic, through opening 8 through the printed circuit board into which a press-in pin 9 is pressed is situated at the location at which the test patterns are located. This press-in pin 9 produces the one connection between the outer layers 12 as well as the test pattern layers 6 and 7. To test whether outer and interior layers are arranged with proper registration, a test bore is then implemented at a prescribed location with the assistance of a drill 17. If the drill strikes an interior layer of a test pattern, the voltage applied between the outer layer 12 of the printed circuit board and interior layers 6 and 7 of the test drill pattern collapses, so that whether or not the drill strikes copper in the interior layers can be identified with the assistance of an electrical throughfeed measurement. The evaluation electronics 1 registers the collapse of the voltage that is applied between the outer and interior layers when the drill 17 strikes copper. 
     The test drill pattern, for example, should then be executed as shown in FIG. 4. When, as shown, a slanting row of holes is placed over this test pattern, one obtains the data chain 0001111. The data chain is acquired and evaluated by a desk top computer connected to the evaluation electronics. It is acquired and evaluated simultaneously with the drilling event of the test pattern. The actual position of the middle of the test pattern with reference to the zero point of the drill can be identified from this data chain and from the known positions of the test pattern bores. Given employment of a plurality of test patterns as shown, for example, in FIG. 5, conclusions about the distortion and offset of the active grid field 11 can be drawn from the rated and actual positions of the patterns, so that the receptacle plates can be moved from a rated starting position into a corrected actual position. 
     Linear, systematic errors of the position sensor or path-measuring system of the drill--as caused, for example, by fluctuations of the operating temperature--, have no influence on the drilling precision, given application of the bore pattern optimization. 
     Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that we wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within our contribution to the art.