| 摘要 |
<p>An immersion tin coating (at least 99% Sn, remainder Cu) is produced on aluminium or its alloys, in preparation for electroplating, by immersing cleaned aluminium, e.g. for between 5 and 40 seconds, in an aqueous solution, e.g. at between 32 and 65 DEG C., composed of 23-59 g./l. of Sn+4 ions (added as K2Sn(OH)6), 6-15 g./l. of CN ions (added as alkali metal cyanide), 1-3.5 g./l. of OH ions (added as alkali metal hydroxide) and 1.5-11.5 g./l. Cu+ ions (preferably added as CuCN, but possibly as stannate or potassium copper cyanide), sufficient alkali metal cyanide being added to complex the copper. At least 20% mole of alkali metal present in the solution is preferably potassium, the remainder being sodium; ideally all the alkali metal is potassium. A tin-copper alloy, e.g. between 40 and 60% Sn with remainder Cu, is then electrodeposited on the initial immersion tin coating from a bath having the same composition as the above immersion bath, e.g. using current densities of 1-15 amp./sq.dm. for conventional batch plating but up to 150 amp./sq.dm. for continuous wire or sheet plating. Other metals may be deposited directly on to the thin tin immersion coating, e.g. Cu, Sn, bronze and Ni; or on to the tin-copper electrodeposit, e.g. bronze (from a cyanide bath), copper (from a pyrophosphate copper bath), nickel (from a Watts' nickel solution), chromium and also Sn-Ni, Cu-Ni-Cr alloys. Preferably the metals are electrodeposited from baths having a pH value between 4 and 9. Multi-alternate layers of tin and tin-copper alloy may be deposited by interruption of the current. For Cu+ contents as low as 1.5 g./l, such materials as tartrates, citrates, gluconates and saccharates may be added to the above baths.</p> |
