GB1355933A - Mounting of semiconducto' devices - Google Patents

Abstract

1355933 Mounting semi-conductor devices FERRANTI Ltd 26 Jan 1973 [29 Jan 1972 30 Aug 1972] 4259/72 and 40169/72 Heading H1K A strip 10 (Fig. 1) comprises plural identical carrier lead frames 11 for supporting semiconductor devices uniformly distributed axially and longitudinally, and supported on a plastic insulant strip 13. Sprocket holes 15 are uniformly punched along the longitudinal edges, and the lead frames are formed from Ag evaporated on the substrate by known photolitho etching, leaving the Ag layer untouched between the frames and subsequent electrolytic deposition of Sn (Fig. 4). The semi-conductor contacts register for connection with end portions 16 of conductors 14 of the frames. The strip is fed between reels 24 (Fig. 2) over a work-table 22 by rotatable sprockets 23 engaging holes 15, under a plastic masking strip 25 (Fig. 3) fed between reels 27 over idlers 28 by holes 26 engaged by wheels 23; the holes differing in size and spacing from holes 15 to allow for curvature of sprocket wheels 23. The masking member is preformed with square apertures 30 uniformly distributed along its length and spaced so as to expose in sequence the inner ends 16 of conductors 14 of each lead frame 11 (Fig. 3) and to fit the square semi-conductor devices 21 to be mounted (Fig. 4) so as to register with the conductor ends, the solder contacts 32 of the latter, formed on aluminium conductors of the passivated surface by chemically depositing Zn and Ni layers to take the solder. Devices 21 may be inserted manually or automatically by indexing suction transfer, into the successive apertures 30, and after insertion the strip 10 is locally heated at 38 to melt the solder contacts which may conjoin with ends 16. The surface is swept by glass fibre brush 58 to be contiguous with the leading edge of the aperture, and the strip 10 is separated from the masking strips 25 at the second sprocket wheel 23 and wound on reel 24. Each carrier lead frame 11 and associated s/c device is severed from strip 10, the plastic layer is removed, and the outer ends of conductors 14 are soldered to corresponding conductors of a larger lead frame (Fig. 5, not shown) of Ni plated with Ag, stamped from a composite sheet; and each s/c device is encapsulated in moulded epoxy resin (Fig. 6, not shown) and the boundary of the lead frame 41 is removed to leave discrete conductors protruding. The larger lead frames may be formed as a strip transportable by a sprocket holes to receive plural s/c devices and their conductors for simultaneous encapsulation and severance of redundant conductor material; the process being automatically stepped. In a modification (Figs. 7, 8, 9, not shown), the lead frame strip and the masking strip are arranged to accommodate square semi-conductor elements having connection electrodes disposed along all sides, and registering solder protrusions are deposited on the ends of the registering lead frame conductors. The lead frame strip is stamped out of sheet metal without use of a plastic support strip, and after processing is wound on a reel with an interposed insulant sheet. The masking member of the processing apparatus may have a single aperture and be repetitively placed and removed from its operative position relative to each lead frame by a reciprocating action. Plural semi-conductor devices may be mounted simultaneously in a multi-head apparatus. Testing means for the mounted semi-conductor devices may be incorporated. The individual conductors 14 may be individually isolated by etching during formation. Alternatively the lead frames may be of Cu instead of Ag, and the device may be encapsulated in an evacuated enclosure sealed to the lead frames. The main lead frame is replaceable by a header.