Thorn Security Ltd v Siemens Schweiz AG

A patent claim requiring wax to facilitate through-plating and soldering requires a practical benefit. A measurable alteration to a coating’s physical properties is insufficient unless it makes those operations easier in use. Where the claim requires a film to be fused onto a printed circuit board by heat, the fusion must be caused by heat alone, not by pressure after heat has merely put the film in an optimal condition.

For Patents Act 1977 registration provisions, an assignment in section 33(3)(a) can include an assignment by operation of law through universal succession on a corporate merger. It does not, however, include a mere agreement to transfer a patent which has not itself transferred the property.

Siemens, the registered proprietor of a patent for a wax-containing protective coating for printed circuit boards, succeeded before Mann J on validity, infringement and entitlement to damages or an account of profits. Thorn appealed the findings of infringement and the ruling that Siemens could not recover for infringement before its registration as proprietor.

The infringement appeal concerned whether Thorn’s coating, containing 5 per cent wax, practically facilitated through-plating and soldering, and whether it was fused to the board by heat alone. The assignment appeal concerned whether the transfer of the patent through Swiss corporate mergers was an assignment within section 33(3) of the Patents Act 1977 for the purposes of section 68.

1. Appeal allowed on both issues; respondent’s notice dismissed. Thorn’s product did not infringe claim 1. The judge’s conclusion that wax had the required facilitating effect could not stand. The claim imposed a performance requirement: wax had to produce a practical benefit in through-plating or soldering, rather than merely alter flow, viscosity or softening properties.

2. The evidence did not prove a practical benefit in Thorn’s product. At normal soldering-iron temperatures there was no material practical difference in penetration between waxed and waxless coatings. The suggested reduction in charring risk and benefit from a lower-temperature soldering iron were theoretical and unproved. Nor could the judge safely infer, without expert evidence, that wax made removal by hot air easier when lower viscosity and increased wettability pointed in opposing directions.

3. The claim phrase that the film is fused onto the board by the action of heat meant fusion by heat alone. On Thorn’s product and process description, heat placed the patch in an optimal condition for adhesion, but pressure caused the adhesion. The required integer was therefore absent independently of the facilitating integer.

4. On the assignment issue, section 33(3)(a) of the Patents Act 1977 required a purposive construction. In this context, assignment was wide enough to include the automatic vesting of all assets and liabilities in a surviving company by universal succession on a merger. That reading fulfilled the registration purpose of section 68 and was not prevented by section 30(6), which governs assignments effected by documents. A mere agreement to transfer, not followed by a formal transfer, remained outside section 33(3).

5. The judge’s contrary decision on section 33(3), including his earlier decision in Tamglass, was set aside. The court expressed only provisional views that section 33(3)(e) concerns dispositive orders or directions involving judgment or discretion; a ministerial registry entry did not itself transfer the patent.

• Court of Appeal (Civil Division): Allowed Thorn’s appeal, reversed the infringement finding and held that the Swiss merger transfer was an assignment within section 33(3)(a) of the Patents Act 1977.
• High Court (Chancery Division), Mann J: Held the patent valid and infringed, and held that Siemens could not recover damages or an account for infringement before registration as proprietor.