GB1502977A - Multilayer printed circuit boards - Google Patents

Abstract

1502977 Printed circuits INTERNATIONAL COMPUTERS Ltd 26 July 1976 [19 Sept 1975] 38462/75 Heading H1R A printed circuit board (Fig. 1) comprises an insulant substrate of, e.g. phenolic or epoxy resin, ceramic or glass with an array of circuit conductors 4 on face 2 for formed or mounted components (not shown) and a ground or power supply screen 5 having retriculated apertures is mounted on opposed face 3. The screen (Fig. 2, not shown) may be formed as an openwork lattice with apertures and conductors proportional to provide a continuous conductive plane effective to match the natural characteristic impedence of conductors 4 (forming transmission lines) to the requirements of the circuit. Alternate apertures of the rows and columns of the lattice may be omitted (Fig. 3, not shown) and the apertures may be rectangular or diamond shaped (Fig. 4, not shown) to provide a trellis configuration. Circular apertures may also be used, and they are disposed in a regular pattern to provide even distribution of conductive material over the area of the screen providing the required impedance matching. The screen may be continuous over some areas of the board and omitted over others, e.g. those on which a discrete component is mounted. In a multilayer printed circuit board (Fig. 5) a central insulant substrate 13 carries orthogonal strip conductor patterns 14, 15 on either face with interconnection over through holes (not shown). Insulant layers 16, 18 over conductors 14, 15 carry lattice screens 17, 18 acting as power and ground planes with connections to the circuitry of conductors 14, 15 over through holes (not shown) and covered by external protective layers. Alternatively (Fig. 6) the screens may be positioned interiorly of a multilayer board; screens 20, 21 with circular apertures 23 acting as power and supply planes on each face of a central insulant substrate 22; the circuit conductors 24, 26 being carried by insulant layers 25, 27 over screens 20, 21 with interconnections through plated through holes (not shown) traversing clearance apertures of the insulant layers and of the screens. External protective layers may be provided. Different aperture patterns may be employed for different screens, and selected screens may be imperforate, to provide required impedence matching. The spacings between conductor layers and screens may be varied in different areas.