PLASMA DEPOSITION METHOD

1 . A plasma deposition method in which a cover layer is deposited onto the internal walls of an empty plasma chamber by plasma deposition of a precursor mixture comprising (i) one or more hydrocarbon compounds of formula (A), or (ii) one or more C 1 -C 3 alkane, C 2 -C 3 alkene or C 2 -C 3 alkyne compounds:

wherein:

Z 1 represents C 1 -C 3 alkyl or C 2 -C 3 alkenyl;

Z 2 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl;

Z 3 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl;

Z 4 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl;

Z 5 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl; and

Z 6 represents hydrogen, C 1 -C 3 alkyl or C 2 -C 3 alkenyl.

2 . The method according to claim 1 , wherein the plasma deposition is plasma enhanced chemical vapour deposition (PECVD).

3 . The method according to claim 1 or 2 , wherein the plasma deposition occurs at a pressure of 0.001 to 10 mbar.

4 . The method according to any one of the preceding claims, wherein the or each hydrocarbon compound of formula (A) is selected from 1,4-dimethylbenzene, 1,3-dimethylbenzene, 1,2-dimethylbenzene, toluene, 4-methyl styrene, 3-methyl styrene, 2-methyl styrene, 1,4-divinyl benzene, 1,3-divinyl benzene, 1,2-divinyl benzene, 1,4-ethylvinylbenzene, 1,3 -ethylvinylbenzene and 1,2-ethylvinylbenzene.

5 . The method according to claim 4 , wherein the hydrocarbon compound of formula (A) is 1,4-dimethylbenzene.

6 . The method according to claim 4 , wherein the one or more hydrocarbon compounds of formula (A) is a mixture of 1,4-divinyl benzene, 1,3-divinyl benzene and 1,2-divinyl benzene.

7 . The method according to any one of the preceding claims, wherein the precursor mixture further comprises one or more reactive gases selected from N 2 O, NO 2 , NH 3 , N 2 , CH 4 , C 2 H 2 , C 2 H 6 , C 3 H 6 and C 3 H 8.

8 . The method according to any one of the preceding claims, wherein the precursor mixture further comprises one or more non-reactive gases selected from He, Ar and Kr.

9 . The method according to any one of the preceding claims, wherein the thickness of the cover layer is from 5 nm to 1000 nm.

10 . The method according to any one of the preceding claims, wherein deposition of the cover layer is preceded by pre-treatment step in which the adhesive properties of the internal walls of the empty plasma chamber are modified.

11 . The method according to any one of the preceding claims, wherein deposition of the cover layer is followed by surface treatment of the cover layer to modify its adhesive properties.

12 . The method according to any one of the preceding claims, wherein following deposition of the cover layer:

(a) an object is introduced into the empty plasma chamber,

(b) a conformal coating is deposited onto the object by plasma deposition to provide an object with a conformal coating, and

(c) the object with a conformal coating is removed from the plasma chamber.

13 . The method according to claim 12 , wherein steps (a) to (c) are repeated one or more times.

14 . The method according to claim 12 or 13 , wherein the object is an electrical assembly.

15 . The method according to claim 14 , wherein the electrical assembly is a printed circuit board.

16 . The method according to any one of claims 12 to 15 , wherein, following removal of the object with a conformal coating from the plasma chamber, the cover layer and any materials deposited thereon during deposition of the conformal coating are removed from the internal walls of the plasma chamber.

17 . The method according to claim 17 , wherein the cover layer and any materials deposited thereon during deposition of the conformal coating are removed by a physical cleaning technique.