Patent GB-1305337-A (GB)
IPC: H01L23/495
Filed: 1971-08-24
Abstract: 1305337 Manufacturing lead frames; angular bending; sub-press mechanisms AMP Inc 24 Aug 1971 [8 Sept 1970] 39754/71 Headings B3A B3E and B3W [Also in Division H1] A method of manufacturing lead frames in the form of continuous strip metal stock 30 comprises the steps of blanking the strip stock in a die set (48), Fig. 1 (not shown), to form a succession of side-by-side lead frame blanks each comprising a heat sink 4, three spaced, parallel leads 6, 8, 10 connected to each other by an integral tie-bar 16, a connecting strap portion 12<SP>1</SP> attached to the centre lead, and contact arms 20<SP>1</SP> attached to the leads 6, 10, bending the contact arms laterally of the plane of the strip in directions generally towards each other, bending the strap portion 12<SP>1</SP> to dispose the leads in a plane perpendicular to the plane of the strip, forming the contact arms to their final position, Fig. 3C (not shown), and bending the strap portion to dispose the leads in a plane which is parallel to, but spaced from, the plane of the strip, the contact arms being located between the respective planes. The strip 30, Fig. 3D (not shown), e.g. nickel plated, copper alloy stock, comprises a relatively thick portion (32) and a relatively thin portion (34) in transverse cross-section, with a pre-applied solder strip 26<SP>1</SP> overlying the two portions. It is passed through the stamping and forming die set (48) with the punching operations to form openings 36, 38, 39, 40, 42 having been carried out previously. The initial punching operations are followed by the dishing of the leads 6, 8, 10 by dies 64, Fig. 2, in co-operation with suitable punches at station 62. At station 43 the contact members are formed downwardly with respect to the strip using a tool provided by a reciprocating slide 70. Then there are further bending operations to dispose the contact arms such that they are spaced apart by a distance greater than the width of the strap portion. Tool (93) and camming punch (114), Figs. 6, 7 (not shown), are utilized for this purpose. Slide 70 is then retracted and the strip is fed to subsequent forming stations. Punching operations are carried out at station 120 to remove unnecessary material from the strip and a coining operation for forming the sides of the heat sink 4 is carried out at station 122. At station 44 the strap portion 12<SP>1</SP> is bent at its forward end 13<SP>1</SP> so as to orient downwardly the leads in a plane perpendicular to the plane of the strip, the contact arms lying in the same plane, Figs. 8, 9 (not shown). The ends 24 of the contact arms are then bent inwardly and given their final configuration at station 45 using a slide member (138) and a punch (140), Figs. 10-14 (not shown), the ends 24 now being spaced apart by a distance less than the width of the strap portion. The strap portion is then again bent, at station 46, at bend 15 adjacent to the edge (14) of the heat sink 4 so that the leads are also rotated through 90 degrees and disposed in a plane parallel to, but above, the plane of the heat sink. The soldered surface of ends 24 now face the heat sink surface to permit soldering to a transistor chip (not shown). The strap portion is then further formed, Figs. 17, 18 (not shown), to increase the bend angles at 13<SP>1</SP>, 15 until the portion extends obliquely between the planes defined by the leads and the heat sink so as to locate the ends 24 of the arms at predetermined positions above the heat sink surface. Subsequently, there is a final sizing operation to precisely control the dimensions of the finished frame, the spacing between the planes of the heat sink and leads being determined by a projection (200), Figs. 19-21 (not shown), which depends from a sizing tool (198).