Patent GB-1523478-A (GB)
Title: Convoluted resistive-capacitive devices an methods of forming them
IPC: H01G4/40
Filed: 1975-12-12
Abstract: 1523478 Printed circuit RC network assemblies; turret machines WESTERN ELECTRIC CO Inc 12 Dec 1975 [17 Dec 1974] 51109/75 Headings H1J and H1R A resistance capacitance network device 20 (Fig. 4) comprises a roll 20r wound from strips 21, 22 (Figs. 1, 2) of flexible dielectric material, e.g. polycarbonate, polystyrene, or polyester and conductive layers 23, 24 of aluninium, silver zinc or alloys thereof coated on the strips by, e.g. vapour deposition or sputtering; the metallized strips being formed, e.g. by slitting a single metallized strip to have identical characteristics. Each strip has metallized edges 21m, 22m and opposed non-metallized borders 21n, 22n and they are offset during winding. Then the outer convolutions of roll 20r are masked adjacent their ends and spray soldered to form porous end blocks 20s, after which the roll is vacuum impregnated with wax. Terminal leads 20t are attached and the device is encapsulated. During winding, demetallized gaps 26, 27, 28 are formed in metal layer 23 of strip 21 adjacent metallized edge 21m to define a lead termination area TA1 equal resistance paths R 1 , R 2  and path CS1 connecting area TA1 to the resistance paths, which in turn extend oppositely to capacitance electrode area 23c. Gaps 26, 28 extend from opposite ends of layer 23 in alignment and are symmetrical of centreline 26mp. Gap 27 is likewise symmetrical of the centreline and parallel to gaps 26, 28. For HF stability layer 24 has a lead termination area TA2 corresponding to TA1 and defined by gaps 29, 31 in metal layer 24 corresponding to gaps 26, 28 of layer 23. The equivalent electrical circuit comprises (Fig. 5) equal resistances R 1 , R 2  in parallel and in series with resistor R 3  capacitively coupled to equivalent resistance R 4 ; the whole being in series with equal resistances R 5 , R 6  and termination resistances R t  defined by the region between the lead terminations and solder blocks 20s. The lead termination areas TA1, TA2 defined by gaps 26, 27, 28, 29, 31 are radially located of the centre and outer periphery of the roll for good electrical connection between blocks 20s and the termination areas, while resistances R 1 , R 2  are located adjacent metallized edge 21m and one end of the roll to improve protection on impregnation and to ensure they are opposed to the non-metallized edge 22n of the other strip. In winding apparatus (Fig. 6) metallized strips 21, 22 are fed from spools 32, 33 over guides 24 and wound upon an arbor 36 which is split so that opposed halves define a strip retaining slot when closed and overlapping. The halves are mounted on respective discs of a turret 37 carrying an identical split arbor 38, which is rotatable 180 degrees into the position shown in Fig. 7, after a network roll has been wound; the arbor 38 being closed to receive the strips. After an initial turn thereof strips 21, 22 are cut by a blade 39, the winding on arbor 36 is completed, the roll is wrapped in plastic tape and the arbor is opened to allow removal of the roll. Thereafter winding proceeds on arbor 38 in succession. The incoming strips receive radiation from a pulsed laser 41, e.g. of neodymium doped yttrium aluminium garnet directed on splitting mirrors 48, 49 to produce beams 42, 43, 44 controlled selectively by reciprocable shutters 46, 47, and the beams 42, 43 are reflected through lens 53 to a focal point on the opposite side of strip 21 so that the beams intersect the metal layer 23 and cut gaps 26, 27, 28 at a spacing preset by the adjustment of leans 52; the remaining laser energy being absorbed by diffuser 54. Beam 44 intersects metal layer 24 of strip 22 through mirrors 56 and lens 57 to cut gaps 29, 31 therein, and the remaining energy is absorbed by diffuser 58. The fumes are removed by exhaust chambers 59, 62 adjacent the point of impact of the beam. Operation of the shutters 46, 47 at appropriate cyclic times enable intervals to be left in the laser cut gaps of the metal layers in response to control apparatus (Fig. 9, not shown) wherein a pulse generator linked to the dielectric film travel over a guide roll produces pulses proportional to its speed, which operate a digital laser pulse control circuit 64 to feed a digital counter system 66. This operates control signals for the reciprocal shutters 46, 47 on preselected counts and includes a downup counter 67, a unit length switch 68 controlling the network capacitance, a first line switch 69 controlling the size of the lead termination areas TA1, TA2 for the metallized films 21, 22 and a second line switch 71 controlling resistance values R 1 , R 2 . Thus the start of the winding machine, the position and length of the laser gap cutting, the indexing of the winding turret, the cutting of the strip, and stop and restart of the machine are controlled in sequence by the timing circuits, the laser pulsing circuits being synchronized with the strip speed and the shutter operating circuits in sequence. The system is adjustable to permit variations of capacitance and resistance of the units. Resistivity of the metal layer is measurable on line by a digital voltmeter between spaced rollers, and applied to control the gap lengths by shutter operation to obtain required resistance paths R 1 , R 2 . Extraneous HF signals are filtered out by the laser pulse control system 64 to prevent malfunction, and under conditions of excessive pulse frequency arising from undue strip speed the pulsing is inhibited and the winding machine is shut down. At the beginning of each run blank sample network rolls are wound with laser inhibition, to which solder blocks and leads are attachedto enable the values of the termination resistance Rt to be checked and corrected. Suitable circuitry (not shown) may be provided to vary the laser power input with its pulsing frequency to stabilize the gap widths, while optical means are provided (Figs. 10, 11, 12, not shown) whereby the laser cut gaps at the outer end portions of the strips are given a zig-zag form at their cut ends during the indexing cycle, so as to prevent possible short circuiting of the capacitance elements by the metallized portions of the outer ends of the strips.