GB1502006A - Manufacture of printed circuit boards and the like - Google Patents

Abstract

1502006 Computer aided circuit design MARCONI CO Ltd 26 April 1976 [4 Oct 1975] 40733/75 Heading G4A An artwork master fron which a printed circuit board or the like (e.g. an MOS circuit) may be produced is formed by using a computer, in a first stage, to determine the position of a conductive track required to interconnect two circuit points by determining the positions of points 37-41 each representing the point at which the track crosses a grid line A-G and, in a second stage, to determine from the points the lengths and positions of horizontal and vertical track sections, e.g. 42, required to form the track, by instructing the computer to modify the position of one or more of the points derived, and by causing the computer to repeat the second stage above to produce an amended result. Double sided circuit boards are produced with pins arranged in rows and columns and with conductive tracks interconnecting desired pins, vertical track sections being formed on one surface of the board and horizontal track sections on the other, plated "through holes" being provided to interconnect vertical and horizontal sections as appropriate. The computer operates automatically in two stages, firstly to route a connection between two specified pins using a system of priorities, e.g. by progressing from left to right across the board until a free vertical track space is located and continuing the process until the track has reached the same vertical position as the second of the two pins. Thus the locations of points 37-41 are determined. In the second stage the computer calculates the positions and lengths of the appropriate vertical and horizontal track sections where possible. However, as is the case in Fig. 5 with section 48, some sections can not be formed. The operator is presented with a display of the (partial) result and then instructs the computer to reposition one or more of the points at which the vertical track sections cross the horizontal grid lines, e.g. in Fig. 5 the point on track C4 at row HS2 and column VT3 is moved to row HS3 and column VT5. The computer then recalculates the positions and lengths of the track sections and produces a further display which may be the final result or may be corrected further. Further modifications may be made by the operator, e.g. varying the spacing between the horizontal grid lines or exchanging the positions of circuit components to simplify the routing problem. In a preliminary stage prior to the operation described above selected pins in the same row may be interconnected by tracks following a serpentine course as necessary. The operator may instruct the computer by typing instructions or by using a light pen and a computer controlled display. The operator need not consider dimensions which are stored by the computer and used in forming a photographic master which in turn is used to construct the circuits.