| 摘要 |
851,544. Semi-conductor devices. ENGLISH ELECTRIC VALVE CO. Ltd. July 17, 1958 [Oct. 28, 1957], No. 33535/57. Class 37 A method of soldering a semi-conductor wafer to a heat sink comprises providing a reservoir for solder on the edge of the area that is to receive the wafer, filling the reservoir with solder by a preliminary firing and then placing the wafer on the heat sink and fixing the wafer by a second firing. As shown, the heat sink is constituted by a copper base with a ground flat surface 6 in which is a hole 3 approx. # inch deep and about the same diameter to form a well for the solder 4. On the base with its edge in contact with the solder is the semi-conductor wafer 2. The surfaces to be joined are first cleaned by, e.g. washing the wafer in a mixture of nitric and hydrofluoric acids and the base in nitric acid diluted 3 : 1 with water after which a final cleaning and storage in hydroquinone saturated solution is said to be an advantage. The solder used is 60/40 Pb/Sn. with preferably an addition of a small amount, 1 Mgm, of silver during the second firing. The first firing takes place in an atmosphere of hydrogen at 400‹C. the second in the same atmosphere at 500‹C. The first firing step may be omitted if a plug of solder slightly longer than the depth of the reservoir is used the solder being placed in the reservoir and the protruding portion flattened firing then takes place in an atmosphere of hydrogen at about 400‹C. the addition of silver conferring apparently little or no advantage. |
