Siemens Schweiz AG v Thorn Security Ltd

JurisdictionEngland & Wales
JudgeLORD JUSTICE MUMMERY
Judgment Date22 October 2008
Neutral Citation[2008] EWCA Civ 1161
CourtCourt of Appeal (Civil Division)
Date22 October 2008
Docket NumberCase No: A3/2007/2630

[2008] EWCA Civ 1161

IN THE SUPREME COURT OF JUDICATURE

COURT OF APPEAL (CIVIL DIVISION)

ON APPEAL FROM THE HIGH COURT OF JUSTICE

(CHANCERY DIVISION)

MR JUSTICE MANN

HC 04 CO 2060

Before:

Lord Justice Mummery

Lady Justice Arden and

Mr Justice Lewison

Case No: A3/2007/2630

Between:
Thorn Security Limited
Appellant
and
Siemens Schweiz Ag
Respondent

Mr Iain Purvis QC and Mr B Nicholson (instructed by Shakespeare Putsman LLP) for the Appellant

Mr Richard Miller QC and Ms Heather Lawrence (instructed by Pinsent Masons) for the Respondent

Hearing dates : 15-17 July 2008

LORD JUSTICE MUMMERY

This is the judgment of the court to which all of its members have contributed.

Introduction

1

Printed circuit boards (PCBs) are ubiquitous in electronic equipment. Typically a PCB is a non-conductive substrate on which there are metal traces carrying electrical signals. They may be on one side of the substrate or on both. In many cases it is necessary to protect the PCB against damage and against interference with the circuitry by, for instance, condensation which might cause it to short-circuit or by corrosion. This is done by a coating. However, once the PCB has been protected, it may become necessary to alter or repair the circuitry. Typically this will require the removal of the protective coating or part of it.

2

European Patent (UK) No EP 0 577 094 BI claims a “Protective Covering for printed circuit boards and method for their manufacture”. The novel feature of the covering, inspired by packaging of consumables, was that it contained added wax and was fused to the board by the action of heat. It claimed that the addition of wax produced certain benefits, particularly in carrying out repairs. The patent is now owned by the Respondent, Siemens Schweiz AG (“Siemens”), following a series of mergers. It claims that a coated PCB manufactured by the Appellant, Thorn Security Ltd (“Thorn”), and installed in a smoke alarm, infringes the patent. Thorn's PCB is coated with a coating that contains 5 per cent wax. Following a trial of the action Mann J held that the patent was valid and infringed, and awarded damages or, at Siemens' election, an account of profits.

3

There is no challenge to the judge's decision on the validity of the patent. However, with the permission of Jacob and Wilson LJJ, Thorn appeal on the question whether it has been infringed (“the Infringement Issue”). Thorn also appeal, with the permission of the judge, on the question whether Siemens are entitled to recover damages in respect of a period of infringement which pre-dated their registration as proprietor of the patent (“the Assignment Issue”). We deal first with the Infringement Issue.

The patent in suit

4

We can take the description of the patent in suit largely from the judge's judgment. The patent describes the invention as follows:

“The invention concerns a printed circuit board, having a protective coating made from an electrically insulating, thermoplastic material, and a process for manufacturing such a printed circuit board with protective coating.”

5

It goes on to describe the existence of existing coatings, designed to protect from moisture and other environmental effects, and says that protective coatings were usually manufactured from a suitable plastic compound and created by dipping, potting, varnishing, spraying or coating, all of which have disadvantages in presenting difficulties or impossibilities of covering uniformly and in coating sharp edges and points. Coatings made in this way are either liquid or particles. The patent next describes an item of prior art (Toshiba) where a strip of thermoplastic material is applied to the front and rear sides of a PCB and bonded by fusing to form an integrated circuit card. This process has the disadvantage that the circuits are no longer accessible after sealing. The patent goes on to refer to certain plastic films made from “thermoplastic material to which a certain amount of wax is added and which has been used to package certain goods, such as consumables”. It continues:

“Based on this prior art, the object of the invention is to create a printed circuit board with a protective coating of the type referred to above, in which the protective coating does not have the disadvantages of the prior art. In particular, the protective coating can be applied to all parts of the printed circuit board in the shortest time by means of a simple process with low maintenance devices, with uniform layer thickness and virtually complete imperviousness to air and fluids, and allows a specific component to be left free-standing with precision. A further object of the invention is to form the protective coating in such a way that during the entire life of the printed circuit boards, the individual circuit elements can be measured through the protective coating and individual components can be replaced, even after the protective coating has been completed.”

6

To achieve these objects, the printed circuit board with a protective coating according to the invention is characterised in that the protective coating consists of a plastic film made of electrically insulating, thermoplastic material to which a wax is added to improve its flow properties, said wax at the same time facilitating through-plating and soldering operations through the protective coating, and that the geometrical shape of the plastic film corresponds to the area of the printed circuit board to be protected, and the film is fused onto the printed circuit board by the action of heat, so that it covers the printed circuit board in a virtually air-tight and moisture proof manner. Although the claim itself does not specify any particular proportion of thermoplastic to wax, the specification says that according to a preferred embodiment the thermoplastic material will consist of between 70 and 90 per cent of the compound product and the wax will consist of between 30 and 10 per cent. The preferable percentage of wax is 30.

“According to a particularly preferred process, the plastic film is formed from [a] strip by water-jet cutting, is brought to a plastic state by heating after positioning on the printed circuit board and is pressed onto the electronic modules by means of a silicone plug, so as to produce a tightly-fitting topography and to displace existing residual air, and in a final process step the protective coating is fused onto the printed circuit board under the action of further heating”

7

A product known as “Jet-Melt 3748”, manufactured by 3M, is referred to as being a starting material. This was identified as being known as a hot-melt adhesive, that is to say an adhesive which is heated and melted before being used to form the bond required. Jet-Melt 3748 itself contains wax. A second component consisting of wax is then added to the Jet-Melt 3748. Lunarit 3286 is given as an example. A manufacturing process is briefly described:

“The best material proved to be one having a softening point above 100°C or a melting range of 120°C to 170°C, which when solidified on the printed circuit board forms a pore-free coating which is impervious to air and fluids … The film thickness is chosen so that the irregularities on the printed conductor, and especially solder spikes, are reliably coated without tearing the film during fusing. A film thickness of approximately 0.2 to 1.0 mm is usually adequate. Thicker films of several millimetres' thickness can also be used for special applications, for example protecting printed circuit boards which have projecting components or sharp points”

8

At a late stage in the described process:

“The film 16 is then heated to a temperature above the softening point in process step D, but without melting it. In process step E the softened film is pressed over the electronic components by means of a soft silicone plug, the film coming into close contact with the components, so that residual air is displaced. In a final process step the protective coating is fused onto the printed circuit board by further heating. This can be achieved advantageously by means of an infrared heater arranged above the film, or by other means, for example with the aid of hot air or a hot inert gas.

The protective coating 16 formed on the printed circuit board 9 covers the modules 13 to be protected, especially irregularities and points on them, with a layer of uniform thickness which is impervious to air and fluids, and reliably protect them against environmental influences. At the same time, partially exposed locations, for example for switches, potentiometers, test points and the like can easily be obtained without additional cost.”

9

Claim 1 of the patent, divided into convenient integers, claims:

“Printed circuit board for electronic modules, having a protective coating made from an electrically insulating, thermoplastic material,

the protective coating consisting of a plastic film made from an electrically insulating, thermoplastic material

to which wax is added to improve its flow properties,

said wax at the same time facilitating through-plating and soldering operations through the protective coating,

and the geometrical shape of the plastic film corresponds to the area of the printed circuit board to be protected,

and the film is fused onto the printed circuit board by the action of heat,

so that it covers the printed circuit board in a virtually air-tight and moisture-proof manner.”

10

Although the claim begins as a product claim, it changes towards its end to a process. It is, therefore, a claim to a product produced by a particular process. The italicised...

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    ...Infringement of Damages on Transfer, Section 33 Thorn v Siemens [2008] EWCA Civ 1161 Court of Appeal: Mummery, Arden and Lewison LJJ: 22nd In October 2007, Mann J found European patent (UK) No. 0577094 to be both valid and infringed. In this appeal there was no challenge to the decision on ......
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