GB2255450A

GB2255450A - Electrical power supply

Info

Publication number: GB2255450A
Application number: GB9108101A
Authority: GB
Inventors: Paul Radmall
Original assignee: Dowty Electronic Components Ltd
Current assignee: Dowty Electronic Components Ltd
Priority date: 1991-04-16
Filing date: 1991-04-16
Publication date: 1992-11-04
Also published as: WO1992019090A1; GB9108101D0

Abstract

The invention provides a circuit board (1) incorporating an integrally formed electrical power cell (7). By forming the cell within the board (1), the need for a case for the cell (7) and the requirement for connecting wires is eliminated reducing weight and component count over known arrangements.

Description

ELECTRICAL POWER SUPPLY This invention relates to electrical power supplies for circuit boards.

It is generally desirable in electronic products to reduce the size and weight of circuits, and great advances have been made in this regard by the use of circuit boards such as printed circuit boards and integrated circuit components.

However, a limiting factor for battery powered electronic products has been the size and weight of the batteries currently available, which can now be the largest and heaviest components used in such products.

A further problem associated with batteries is the need to connect by clips or wires soldered to the battery the circuit it is to power. This adds undesirably to the component count and the number of operations to be performed to make the circuit.

In order to alleviate these problems, it is proposed according to the present invention to provide a circuit board with an electrical power supply comprising a cell formed integrally in the circuit board.

By forming the cell integrally in the circuit board, it is possible to eliminate the requirement for a separate casing, since in effect the circuit board performs that function. This allows a reduction in size and weight of the power supply, and allows it to be readily accommodated in the available space provided by the board. The cell may be rechargeable or nonrechargeable.

Electrical connections will be made to the cell by means of the electrically conductive surfaces of the circuit board. The electrically conductive surface will be that provided to be etched to a required circuit pattern and to which electronic components are soldered to form a circuit.

Commonly these surfaces are made of copper because of its good electrical conductivity. By making the electrical connections to the battery by the conductive surface of the circuit board the requirement for separate clips or wires is eliminated.

The circuit board may be rigid or, where it is to conform to another shape, such as an inside surface of a case, it may be made flexible. Where it is flexible, the cell is also preferably flexible.

The cell may be formed in a cavity, depression, aperture or blind hole made in the surface of the circuit board by, for example, drilling or grinding. Where a hole is made through one of the surfaces, a vapour or gas proof layer may be provided to seal the hole against the ingress of contaminants and/or the leakage of vapour of gas as the cell operates.

Preferably, the vapour proof layer is electrically conductive to provide an electrical connection to the cell.

The vapour proof layer is preferably sealed at its junction with an adjacent electrically conductive layer of the circuit board by an electrically conductive sealant serving to provide a vapour proof seal and to electrically connect the layers.

Advantageously, the cell is formed within the board before addition of the electrically conductive surface or surfaces. The electrically conductive surfaces will then provide vapour proof layers eliminating the requirement for an additional layer and sealant.

Specific embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a plan view of an electrical power cell and a circuit board in accordance with a first embodiment of the invention; Figure 2 is a section along line II-II of Figure 1; and Figure 3 is a section through an electrical power cell and circuit board in accordance with a second embodiment of the invention.

With reference to the Figures 1 and 2, a printed circuit board 1 has an electrically insulating resin core 2 clad by upper and lower electrically conductive copper layers 3 and 4 respectively.

The copper layers 3 and 4 are selectively etched, in a manner well known, to provide a network or circuit pattern of electrically conductive tracks (not shown). Circuit components 5 are soldered to these tracks to form a circuit. The components 5 may include microprocessors, resistors or other electronic/electrical components to suit the electrical application for which it is designed.

Within a blind square hole which extends through the upper copper layer 3 and the core 2 to an inner surface 6 of the lower copper layer 4 is located an electrical power cell 7.

The electrical power cell 7 is a lithium solid state battery and comprises an anode of lithium metal foil 8 placed in the hole in good electrical face-to-face contact with the lower copper layer 4. A layer of polymer electrolyte 9 is provided over the upper surface of the lithium foil 8.

A composite cathode 10, comprising a polymer and an active cathode material and an aluminium foil backing 11, is provided over the electrolyte layer 9.

The aluminium foil backing 11 provides a vapour proof covering as well as an electrical pick up from the cell 7. A fillet 12 of conductive epoxy sealant completes the vapour proofing of the cell 7 and additionally electrically connects the cell 7 to the upper copper layer 3.

Connection between the cell 7 and the circuit components 5 is completed by through hole plating (not shown) to the lower copper layer 4.

A second embodiment of the invention is shown in Figure 3 in which like parts are given the same reference numbers as for the first embodiment. A cell 7 is in this case formed in an aperture in a core 2 of a circuit board 1 prior to a cladding process in which copper layers 3 and 4 are glued to the core 2. The layers 3 and 4 encapsulate the cell 7 preventing ingress of contaminants.

The copper layers 3 and 4 are then etched in a manner well known to provide a network of conductive tracks to which electronic components 5 are soldered to complete the board 1.

In alternative embodiments of the invention, a number of cells may be provided at different locations in the circuit board and electrically linked in series or parallel to give the required voltage and capacity.

Where the cell is located prior to cladding of the board with the conductive layers the vapour proof layer and sealant may be dispensed with, their function being performed by the conductive layers alone.

Claims

1. A circuit board with an electrical power supply comprising at least one cell formed integrally in the circuit board.

2. A circuit board as claimed in claim 1 wherein electrical connections to the power supply are formed by at least one electrically conductive surface of the circuit board.

3. A circuit board as claimed in claim 1 or 2 wherein the or each cell is located in a cavity in the circuit board and sealed by a vapour and or gas proof layer.

4. A circuit board as claimed in claim 3 wherein the vapour and or gas proof layer is electrically conductive to provide an electrical connection to the cell.

5. A circuit board as claimed in claim 4 wherein the vapour and or gas proof layer is sealed at its junction with an adjacent electrically conductive layer of the circuit board by an electrically conductive sealant to provide a vapour and/or gas proof seal and to electrically connect the layers.

6. A circuit board as claimed in claim 2 wherein at least one electrically conductive surface of the board provides a vapour and or gas proof layer.

7. A circuit board as claimed in any preceding claim wherein the board and cell are flexible.

8. A circuit board substantially as hereinbefore described with reference to, and as illustrated by, the drawings.

9. A method of forming a circuit board comprising providing a core clad with first and second electrically conductive layers, forming a hole through# the first layer, forming a cell within the hole in good electrical contact with the second layer, forming a vapour and or gas proof electrically connecting the vapour and or gas proof electrically conductive layer and the first layer.

10. A method of forming a circuit board substantially as hereinbefore described with reference to and as illustrated by the drawing.