(19)

(11)

EP 0 224 582 A1

(12)

(43) Date of publication: 10.06.1987 Bulletin 1987/24 (21) Application number: 86904232.0 (22) Date of filing: 13.06.1986

(51) International Patent Classification (IPC):  G01R 31/ 26( . ) G01R 35/ 00( . ) G01R 1/ 073( . ) H01L 21/ 66( . ) (86) International application number: PCT/GB1986/000346 (87) International publication number: WO 1986/007493 (18.12.1986 Gazette 1986/27)

(84) Designated Contracting States: AT BE CH DE FR IT LI LU NL SE (30) Priority: 13.06.1985 GB 19850015025 (71) Applicant: PLESSEY OVERSEAS LIMITED Ilford Essex IG1 4AQ (GB)	(72) Inventors: EDDISON, Ian, Gregory Northampton (GB) BUCK, Brian, Jeffrey Northampton (GB) SPARROW, John Towcester Northampton NN12 8BT (GB) (74) Representative: Sorenti, Gino  Intellectual Property Department The Plessey Company plc 2-60 Vicarage Lane Ilford Essex IG1 4AQ Ilford Essex IG1 4AQ (GB)