Patent GB-1171467-A (GB)
Title: Semiconductor Manufacturing Method and Apparatus
IPC: H01L21/00
Filed: 1966-07-08
Abstract: 1,171,467. Forging; soldering; welding by pressure. NATIONAL SEMICONDUCTOR CORP. 8 July, 1966 [8 July, 1965], No. 30898/66. Headings B3H and B3R. [Also in Divisions B5 and H1] In the mass production of semi-conductor devices a plurality of device components are secured in spaced-apart relation to flexible tape at a first station and the resulting tape component structure is advanced through one or more further stations at which other components of the devices are attached to those carried by the tape. In the embodiment spaced groups of three wires are attached to flexible tapes, after which two flats are formed on each wire at a second station. The tape structure is then fed to a third station where double diffused transistor dies are soldered at their collector zones to the two flats on the central wire of each group. At a fourth station wires are thermocompression bonded between the emitter and base electrodes of each die and corresponding flats on the respective outer wires of each group. After cleaning and washing the tape structure is cut into lengths, a number of which are placed in a mould to form a plastics encapsulation around each die and the devices finally tested. Formation of tape-components tructure (Fig. 2).- Gold-plated " Kovar " (Registered Trade Mark) wires 32 are inserted manually or automatically in spaced groups of grooves formed in circumferential ridges flanking a central magnetized track on feed wheel 94 so that their ends. are held against the underlying adhesive surfaces of glass-fibre backed tapes 45, 47 fed from supply reel 102. Further tapes 44, 46 are pressed on by rubber roller 112 to sandwich the ends of the wires. The tape-wire structure is moved forward intermittently to a flattening station 120 consisting of a punch with a pair of flat-tapped projections for forming the flats and a pair of flanking projections, and an anvil. The central part of the latter is flat, while the edges are tapered and co-operate with the longer flanking projections to counter the tendency of the wire ends to bend up during the flattening operation, which is effected by rocking the ball-ended pivoted arm 134 to force the punch down against spring pressure. The processed tape is wound on to a storage reel 52 which is transferred to a die-attach machine. Die-attach machine (Fig. 8).-The tape is drawn off the reel intermittently on to feed wheel 162. The wires fit into mating grooves in a thermally resistant peripheral insert but to further reduce heat loss during bonding are held clear of the groove bottoms with flats horizontal by engagement of these flats with the edges of the grooves. Semi-conductor dice are positioned on the flats of the central wire at the bonding station and a group of three water-cooled welding electrodes 180 automatically engaged with the wire outside of and between the dice by the mechanism shown. While nitrogen is blown over the dice pulses of current are passed between the central electrode and respective outer electrodes to sequentially solder the dice to the wires. The processed tape is wound on to storage reel 50 and this is transferred to an electrode wire bonder. Electrode wire bonder (Fig. 13).-The tape is stepped forward from the reel over feed wheel 80 to the bonding station 210. Rotation of cam-shaft 25 allows clamping arms borne by side members 250 to be sprung against the wire ends to hold them against heated anvil 212. Thermocompression bonding head 220 through which gold wire 218 is fed is then adjusted by movement of ball-swivel lever 236 by the operative who views the wires through a microscope 226 fixed in relation to the head and the wire bonded between the die electrodes and the flats on adjacent wires. Spacer tapes are then applied to prevent damage to the devices when the tape is wound on to reel 68 which is next transferred to the finishing station. Finishing station (Fig. 17).-The spacer tapes are separated at 280 for passage through the station and the tape-component assembly passed through chamber 284 where it is sprayed successively with acetone, alcohol and deionized water. On emergence nitrogen is blown across it to remove moisture drips after which it is dried by downwardly directed jets of hot nitrogen, and if desired, sprayed with resin from intermittent jet 320. In the spray chamber the spray is deflected away from the tape edges by baffles 298 and both here and in the drier the tape edges are protected by special side guides. These consist of laterally grooved laminated " Teflon " (Registered Trade Mark) members. The tape edges run in the grooves which are supplied with cool nitrogen through a series of spaced holes to prevent ingress of solvents and hot gases. Encapsulation.-The processed tape component structure is cut into a number of strips which are placed in a heated common mould to which powdered silicone resin is supplied under pressure through a central port. Knifeedged ridges in the mould are so disposed that on pressing the mould halves together they partially sever the wires emerging from the inner side of each die encapsulation. On removal from the mould each strip is broken along the weakened lines. The relative numbers of the different machines for the various processing steps are selected in accordance with the rates of production of which they are each capable.