| 摘要 |
<p>894,622. Gold alloys. HUGHES AIRCRAFT CO. Nov. 17, 1960 [Dec. 1, 1959], No. 39590/60. Class 82(1). [Also in Groups XXII and XXXVI] An alloy for attaching a lead to a predominantly Al surface of a Si semi-conductor device comprises essentially Au and Sn and has a melting point below 410‹C.; preferably the alloy contains at least 60% Au and at least 16% Sn by weight. When used at a temperature between the melting point of the alloy and 410‹C. the formation of an undesirable Au Al 2 phase is substantially avoided and 'a strong, shallow, etch-resistant bond is produced. As shown, a Si wafer 11 has a P-type region 12, and a predominantly Al electrode 13, formed e.g. by alloying a sphere of Al on the wafer surface at 700‹C. and then cooling. A lead 14 having a dip-coating 15 of Au-Sn (80% :20%) on its end is placed on electrode 13 and heated, preferably at 375‹C.; alternatively, a preformed ring of Au-Sn alloy may be used. Lead 14 may have a Ag core 18 and a Au coating 17: the dissolution of a small quantity of Ag in the bonding alloy reduces the solubility therein of Si needles found in Al-Si eutectic, thus inhibiting the penetration of the bonding alloy towards the P-N junction; this Ag may be dissolved from the lead or directly added, up to 5% by weight, to the Au-Sn alloy. Owing to preferential wetting of a Au-clad Ag lead a narrow "hourglass" bond may form; this may be avoided by adding up to 10% (preferably 2-5%) In to the bonding alloy; use of Au-Sn-In (78%:20%:2%) produces a satisfactory bond as at 16. If, however, a Pt-clad Ag wire is used for lead 14 no In is needed to produce such a bond. Minor additions, e.g. up to 1% Ga, may be made to the bonding alloy.</p> |
