Patent GB-1462058-A (GB)
Title: Radio frequency screening and means therefor
IPC: H05K9/00
Filed: 1973-10-19
Abstract: 1462058 Printed circuit board assembly MICROWAVE & ELECTRONIC SYSTEMS Ltd 3 Jan 1975 [19 Oct 1973] 48942/73 Heading H1R A screening enclosure for a component carrying printed circuit board comprises an, e.g., aluminium diecast housing 10 comprising a rectangular box 20 enclosing a printed circuit board 40 and having a fitted cover 30 thereon (Figs. 1, 2, 3). The printed circuit board has a rectangular area 41 flanked by wings 42 carrying terminal blocks 50 and having locating end notches 43. Circuitry (not shown) is formed on one side 44 of the board for interconnecting components (not shown) mounted on the reverse side 45. Pins of the terminal blocks project through apertures of the wings 42 to connect appropriately to the printed wiring, which is connectible to the components by plated through holes or through pins. The circuit side of the wings is metallized at 42a to extend over the control area of the circuit board 40, which is located in the enclosure by inserts of the latter engaging notches 43. End walls 22 and side walls 23 are ledged at 22, 23a to support the board margins, and metallization 42a contacts pillars 24 of the box at the ledge levels which are also threaded for screws securing the board. Notches 25 allow the entry of cables to the terminal blocks 50. The cover 30 is of corresponding rectangular shape and is flanged and shouldered at 31, 32 to fit the upstanding walls of box 20. Dependent fins 33, 34 defining a rectangular enclosure overlie and contact the inner margins of metallization of the printed circuit board to provide secondary RF screening. Integral threaded pillars 36 aligned with pillars 34 are secured thereto by axial captive screws 37 also securing the printed circuit board. Compartments 26, 38 screen the circuit area and component area of the circuit board, while compartments 39 contain the terminal blocks 50 (Fig. 4) for connecting incoming leads to the board, mounted on insulant elongate body 51 screwed to wing 42; metallized at 42a to contact ledge 23a and fin 33. The elongate body has pairs of side by side holes therealong; one hole 52 of each pair containing a feed-through capacitor 53 located by a shoulder 54. A rebate 55 at the underside of body 51 receives a metal plate 56 contacting metallization 42a. Apertures 57, 58 are aligned with holes 52 of the connector block and an axial feed through lead 57 of the capacitor projects to the underside of wing 42 while the other lead 60 projects upwardly from hole 52 so that a connection through the capacitor is RF decoupled to ground by the body of the capacitor seating on plate 56 contacting metallization 42a while aperture 57 is closed. Lead 59 is soldered to appropriate printed wiring 47 pin connected at 48, and lead 60 engages an aperture of a terminal plate 61 rebated into the top of body 51 and secured by a screw 63 in the second hole of the pair whose lower end is enlarged to admit the securing nut 65. An input cable is secured under the screw head for connection to capacitor lead 60, which is surrounded by ferrite bead 67 so that it operates as a series RF inductance.