WO1988002943A1

WO1988002943A1 - Low impedance electrical conductors

Info

Publication number: WO1988002943A1
Application number: PCT/GB1987/000729
Authority: WO
Inventors: David James Bale
Original assignee: David James Bale
Priority date: 1986-10-16
Filing date: 1987-10-16
Publication date: 1988-04-21
Also published as: GB8624823D0

Abstract

The connector comprises a plurality of laminar conductors (2) arranged in parallel layers separated by layers (3) of dielectric material. The conductors (2) include first conductors (6) mutually connected together by first terminals (8) and arranged in a first series of said parallel layers, and second conductors (7) mutually connected together by second terminals (9) and arranged in a second series of said parallel layers interspersed with said first series of said parallel layers. The terminals (8 or 9) extend through plated through-holes in the conductors to which they are to be electrically connected and through larger holes in the conductors from which they are to remain electrically isolated.

Description

"Low Impedance Electrical Conductors"

This invention relates to low impedance electrical conductors and is more particularly, but not exclusively, concerned with such conductors for use as busbars.

Busbars for supplying d.c. power to multiple electronic circuits may take a variety of forms, and may be connected either to sockets for mounting of printed circuit boards on a back plate or directly to the circuits themselves by means of hard wire connections. However, conventional forms of busbar suffer from problems due to current flow in the common return line. Such problems can cause intermittent or unreliable operation, and, in more serious cases, can lead to a malfunction of the complete electronic system.

In order that the nature of these problems may be more fully understood, the conventional manner of connection of circuits to a busbar will now be described with reference to Figure 1 which diagrammaticall shows three circuits A, B and C connected to a power supply PS. The source impedance of the power supply is very low, and Z1 , Z2 and Z3 represent the common return impedances of the wire connections to the 0V power supply terminal.

If a large current IA flows in the common return line due to an event in circuit A_r voltage drops will occur across the impedances Z1, Z2 and Z3. This will result in an increase in the nominal 0V voltage to circuit B, and also, to a lesser extent, in an increase in the nominal 0V voltage to the circuit C. Such voltage increases may cause state changes in the circuits A, B and C with possible undesirable consequences. If, -for example, A, B and C are TTL type circuits, the effect of such changes will be to reduce noise immunity levels of each TTL device used in the circuits. Voltage drops will also occur in the ÷V line, but this will be less serious since signals which cause changes of state are usually referenced to OV and not to +V. Whilst such problems would cease if- the series line impedances were low enough, it is very difficult to reduce these impedances to acceptable levels since the wire connections may be several inches long and will have finite characteristic impedances. A conventional connection arrangement for circumventing these problems is shown diagrammatically in Figure 2. In this arrangement separate wire connections of impedances ZA, ZB and ZC respectively are connected from the circuits A, B and C to the OV power supply terminal in a star configuration. In this case, it can be seen that a large current IA due to an event in circuit A will not cause voltage drops across the impedances ZB and ZC. However, this method of connection will result in a large number of connection wires many of which may be quite long, and this will increase the possibility of a fast edge on one of the wires giving rise to induced currents in neighbouring wires. This would mean that all such wires would need to be screened to reduce coupling between wires. It is an object of the invention to provide a novel form of. low impedance electrical connector which is capable of being used in a connection arrange- ment such as that described with reference to Figure 1 without giving rise to the problems discussed with reference to Figure 1.

According to the present invention there is provided a low impedance electrical connector comprising a plurality of laminar conductors arranged in parallel layers separated by layers of dielectric material, the conductors including first conductors mutually connected together by first electrical connection means and arranged in a first series of said parallel ^"layers and second conductors mutually connected together by second electrical connection means and arranged in a second series of said parallel layers interspersed with said first series of said parallel layers. Such a connector can be made to be of such low impedance that it can be used in a connection arrangement such as that of Figure 1 without giving rise to problems due to coupling of circuits via_. their common OV^" impedances, as well as in a number of other applications with particular advantage.

In a preferred embodiment the layers in said second series of said parallel layers alternate with the layers in said first series of said parallel layers. The number of layers in each series of layers may be varied considerably according to the required application, but will be typically between 10 and 100.

In addition it is preferred that conductors in adjacent layers are of the same width and are positioned directly one above the other.

If required each layer in each series of layers may comprise more than one conductor, in which case conductors in the same layer will generally be electrically isolated from one another and each will form part of a separate series of first or second conductors. This will then enable separate electrical connections to be made by means of a common electrical connector.

The connector may additionally include outer conductive layers electrically isolated from the first and second conductors. These conductive layers may be connected to a heat sink. The layers of conductors and layers of dielectric material may be bonded together by means of layers of adhesive. Furthermore each of the layers of conductors and layers of dielectric material conveniently has a thickness between 10 and 250 microns, and the width of each conductor is preferably between 1 and 50 mm.

The first and second connection means may each comprise a plurality of connections at a number of connection points spaced along the length of the connector. Each connection preferably includes a respective terminal extending through holes in the layers of conductors and the layers of dielectric material and electrically connected to conductors in one of said first and second series of layers but not in the other of said first and second series of layers. The terminals may serve for connection of the connector to a power supply and to circuits to be supplied by the power supply. In order that the invention may be more fully understood, reference will now be made to Figure 3 of the drawings which diagrammatically shows a portion of a low impedance electrical connector in accordance with the invention.

Referring to Figure 3, the connector 1 shown therein comprises laminar conductors 2 arranged in parallel layers and separated by layers 3 of dielectric material. In addition two outer conductive layers 4 and 5 are provided for connection to heat sinking. The conductors 2 comprise first conductors 6 arranged in a first series of layers alternating with second conductors 7 arranged in a second series of layers.

Although each, of the series of layers is shown in Figure 3 as comprising only three layers of conductors 6 or 7, it should be understood that in practice a considerably greater number of layers will generally be provided, typically of the order of thirty layers. Furthermore the thickness of the layers 3 , 6 and 7 by comparison with their width has been considerably exaggerated in the drawing for ease of illustration, and in practice the width of each layer will be of the order of a hundred times its thickness.

The conductors 6 are connected together by terminals 8 extending through plated through-holes in the conductors 6 and through larger holes in the conductors 7 (so as to remain electrically isolated from the conductor^'s 7). Similarly the conductors 7 are connected together by terminals 9 extending through plated through-holes in the conductors 7 and through larger holes in the conductors 6. In use connections are made from the OV and +V terminals of the power supply to a respective pair of terminals 8 and 9 at one end, or preferably towards the middle, of the connector 1 , and similarly connections are made between other _pairs of terminals 8 and 9 of the connector 1 and the circuits to be supplied by the power supply.

If the above connector is considered as a balanced transmission line, its characteristic impedance ZO will be given by:

where R is the resistance, L is the inductance, G is the conductance and C is the capacitance of the balanced line.

It can be seen from the above expression that, in order to make ZO as small as possible, R and L should be made as small as possible and G and C should be made as large as possible.

By analogy, it can be said that the following conditions should be applied to the connector 1 :

(1) R should be made small by maximising the total cross-section of the conductors 6 and 7 consistent with the limitations on conductor thickness for maximum utilisation of copper imposed by the skin effect discussed below.

(2) L should be made small by maximising the number of layers of conductors 6 and 7. (3) G should be made large by using material of large insulation resistance for the dielectric layers

3. (4) C should be made large by using material having a high dielectric constant (relative permittivity) for the dielectric layers 3, and by having the conductors 6 and 7 as close together as possible consistent with the required operating voltage. C can also be increased by increasing the area of the conductors 6 and 7.

With further reference,to the skin effect mentioned above, at frequencies above 1 MHz current flow in a conductor is restricted to a peripheral zone of the conductor, and the inside of the conductor carries little current. This means that, in such circumstances, for maximum utilisation of copper the conductor thickness should not be much greater than the skin depth determined in accordance with the skin effect. The connector may be fabricated by conventional flexible multilayer printed circuit techniques, the layers being bonded together by an adhesive, such as Pyralux WA/N (registered trade mark). The dielectric layers 3 may be constituted by a paper or a polyamide or tetrafluorethylene film to which the adhesive has been applied on both sides.

A typical specification for a connector 1 manufactured by these techniques is as follows:

Number of layers (each of which incorporates conductors 6 and 7): 30

Length: 42 centimetres

Width: 2 centimetres Copper thickness: 35 microns Thickness: 0.96 centimetres

Current capacity: 35A

Characteristic

Impedance : < 0. 01 J\

DC resistance : < 0.4mΛ

5

Operating voltage: 100V

Typical Capacitance per metre: 0.6 F

Continuous temper¬ ature range: -40 C to + 100°C

Dielectric strength: 2400V 10

The above described connector can be used in a variety of applications to overcome the problems . discussed above with reference to Figure 1. Obvious applications are in the fields of avionics, computers,

,4_P- telecommunications and the like. The connector may be used to help to reduce the effects of lightning discharges and the effect of a nuclear electromagnetic pulse on power supply rails and associated circuits. Areas of application will mainly be associated with digital type 0 systems where large currents (several amperes) with very fast rise times (tens of nanoseconds) are encountered, but applications may also be found with analogue circuits.

Claims

1. A low impedance electrical connector comprising a plurality of laminar conductors arranged in parallel layers separated by layers of dielectric material, the conductors including first conductors mutually connected together by first electrical connection means a d arranged in a first series of said parallel layers and second conductors mutually connected together by second electrical connection means and arranged in a second series of said parallel layers interspersed with said first series of said parallel layers.

2. A connector according to claim 1, wherein the layers in said second series of said parallel layers alternate with the layers in said first series of said parallel layers.

3. A connector according to claim 1 or 2, wherein conductors in adjacent layers are of the same width and are positioned directly one above the other.

4. A connector according to claim 1, 2 or 3, wherein each layer in each series of layers comprises more than one conductor.

5. A connector according to claim 4, wherein conductors in the same layer are electrically isolated from one another, and each conductor in a layer forms part of a separate series of first or second conductors.

6. A connector according to any preceding claim, further comprising outer conductive layers electrically isolated from the first and second conductors.

7. A connector according to any preceding claim, wherein the layers of conductors and layers of dielectric material are bonded together by means of layers of adhesive.

8. A connector according to any preceding claim, wherein each of the layers of conductors and layers of dielectric material has a thickness between^* 10 and 250 microns, and the width of each conductor is between 1 and 50 mm.

9. A connector according to any preceding claim, wherein the first and second connection means each comprises a plurality of connections at a number of connection points spaced along the length of the

„connector.

10. A connector according to claim 9, wherein each connection includes a respective terminal extending through holes in the layers of conductors and the layers of dielectric material and electrically connected to conductors in one of said first and second series of layers but not in the other of said first and second series of layers.