Patent GB-902530-A (GB)
Title: Improvements in and relating to methods of and apparatus for attaching minute members to bodies
IPC: H01L21/00
Filed: 1958-09-26
Abstract: 902,530. Control of two motors. PHILCO CORPORATION. Sept. 26, 1958 [Sept. 26, 1957], No. 30810/58. Class 38 (3). [Also in Groups XXXVI and XL (c)] A minute member such as a whisker, is attached to a semi-conductor or other body by cutting, plating or otherwise treating an end of the member while it is located in a fixed position and then attaching the member to the body while it is still substantially in this fixed position. Figs. 1 and 4 show the general arrangement. A wire-feeding element 81 comprising jaws 111 and 112 is mounted by a vertically adjustable arrangement on a horizontally movable table 124, to grip and provide a length of wire 103 from reel 104. A tank unit 11 containing a heated plating solution is then raised so that the wire is covered to a precisely predetermined depth, and electrolytically plated in accordance with a precise timing control. The apparatus (Fig. 11, not shown), includes means for exhausting any vapours during plating to avoid deposition on undesired surfaces, and a thermo-couple is used as part of the temperature control system. After tank 11 is withdrawn, the wire is gripped by gripping element 82, the jaws 111 and 112 of unit 81 release, move upward and regrip the wire which is then cut-off and bent by jaws 631 and 632 of cut-off unit 83 as shown in Fig. 32. Unit 83 is also mounted on table 124 by means which allow for rigid, horizontal movement so that the jaws can be advanced to the wire for the operation and then withdrawn. Holder 13 which carries the semiconductor wafer to which the wire is to be soldered is then moved into position at the end of the whisker. Holder 13 is mounted on the fixed frame 55 by means allowing for rigid but controlled vertical movement and the carrier slide member immediately supporting the semiconductor wafer is capable of precise horizontal movement. When the semi-conductor wafer is positioned under the whisker 103 an optically controlled servomotor system operates to move table 124 and thus the whisker 103 in horizontal X and Y directions to position the whisker precisely over the desired region of the wafer. This is necessary since although the wafer is correctly positioned relative to a fixed Z axis, the whisker position may have varied slightly due to the bending and feeding operations. The position of the wafer relative to the Z-axis is assured by fixing this in position on carrier 13 before any desired operations on the wafer are performed; any such treatment, e.g. jet etching of the wafer to form a small pit, are effected with precise positioning of the apparatus concerned so that the location of the pit, for example, lies exactly on the predetermined Z-axis. When the whisker is correctly located in the horizontal plane, the wafer on carrier 13 is raised to a position slightly above that at which contact with whisker is established to provide a predetermined pressure. A heating element 277 (Fig. 9), associated with jaw 252 of gripping element 82 then operates to heat the whisker 103 by conduction, melting the plated layer of solder (Fig. 39) to solder the whisker to the semi-conductor wafer 351. The operation is completed by withdrawal of the gripping element 82 and the semi-conductor wafer on holder 13 from which it is ejected. The final form of the electrode is shown in Fig. 45, which shows a surface barrier transistor before the second electrode is added. The various operations may be controlled manually or automatically. The horizontal and vertical movements are effected by pneumatic apparatus in conjunction with mechanical linkages which are described in detail. Electrical timing and switching means control the duration and limits of the movements but these are not described in detail except for the mechanical operation of limit switches. The movements are extremely precise, many movements being arranged to take place firstly at a relatively fast rate and then slowly to provide fine control. Fig. 17 shows details of the optical-servocontrol apparatus. A light source 17 (see also Figs. 1 and 4) is mounted on table 128 (fixed to frame 55) by pillar 404 and a telescope 408 associated with a photo-electric unit 410 is similarly mounted. A second source and telescope arrangement is provided, the two arrangements covering the X and Y-axes respectively. The system is arranged so that an image of whisker 103 is produced either on screen 413 for visual inspection or on the photocell according to the position of mirror 411. Associated with the cell is a light chopper and shutter arrangement whereby alternate halves of the image provide an amplifiable signal which is fed to a servo-control stage (not described in detail) to operate motor 18 which moves an intermediate table 129 carrying table 124 in the X-direction until the whisker is centrally positioned. The second light source and telescope arrangement operates similarly, the motor in this case moving table 124 to position the whisker on the Y-axis. A microscope is provided for initial adjustment of the apparatus. The mirror is automatically tilted for the short interval of time during which adjustment is effected.