Patent GB-1353242-A (GB)
Title: Joining of workpieces by explosive bonding
IPC: H01R12/00
Filed: 1971-04-19
Abstract: 1353242 Welding by pressure WESTERN ELECTRIC CO Inc 19 April 1971 [29 Jan 1970 31 Aug 1970] 20495/71 Heading B3R [Also in Division H1] In making an electrical device or circuit including bonding a first workpiece consisting of one element of the device or circuit to a second workpiece consisting of a second element of the device or circuit, the regions of the workpieces to be bonded are placed in juxtaposition and an explosive is detonated adjacent the juxtaposed regions, the explosive consisting solely of a primary explosive. The explosive may be nitrogen iodide; the azide of lead, silver, titanium, boron, silicon, mercury, copper, cadmium or ammonia; the fulminate of mercury, silver or copper; the acetylide of mercury, copper or silver; the styphnate of lead or barium; the nitride of silver; tetrazene or diazodinitrophenol (DDNP). In an embodiment a number of beam lead integrated circuit devices 31, Fig. 1, are temporarily secured to a plate 30 located in a bore 33, a stencil plate 40 having slots 41 therein is fitted into the box so that the slots overlie the beam leads and a squeegee 43 is rolled over the plate 40, on which explosive material preferably in a solution has been deposited, to force the explosive on to the leads of each device. Side screen printing may be used as an alternative. The devices 31 are removed from the plate 30 with a small quantity of explosive 48 on each beam lead. One such device 31 is arranged on a ceramic or glass substrate 52, Fig. 4, with the beam leads, e.g. of gold 42 carrying explosive 48 bent at an angle to metallic, e.g. gold lands 50 and detonator of the explosive 48 is effected by an electrical discharge. The substrate temperature is preferably raised to 175 C. prior to passing the electrical discharge. After bonding the beam leads are flattened with a small area of pitting in the area occupied by the explosive. The bonding surface of the beam lead may be undulating or castellated. To protect the device from explosion products the bonding may be effected in an evacuated bell jar or by effecting bonding through a buffer layer of polyimide or stainless steel. In an example an apertured buffer layer 60, Fig. 6, is placed over the device 31 with explosive material 48 on its upper surface, the explosive having been deposited by the device of Fig. 1, by silk screen printing or by depositing it into recesses by a roller having a raised surface. The sheet 60 may be contoured rather than apertured and if of plastics material may be left in place after bonding. The explosive employed on the beam leads may be, e.g. silver azide and may be detonated in a vacuum jar by light produced by krypton filled quartz flash lamps, with or without an explosive carrying transparent buffer layer. A laser beam or a quartz incandescent lamp may be used instead of the flash lamps and for detonation by light 28% gold powder may be mixed with silver azide powder. The explosive may be detonated by flowing a chemical atmosphere over the explosive or by withdrawing an inhibiting chemical atmosphere from over the explosive. Heat may be applied to the substrate to effect detonation or radio frequency currents may be induced in the metallic portions of the assembly to heat the beam leads above the detonation temperature or dielectric heating may be employed. Acoustic energy derived from an acoustic horn may be directed at the explosive to detonate it, with bonding taking place in flowing inert gas, or mechanical pressure may be applied to the explosive by a tool acting through a sheet of plastics material or aluminium. A spark may be struck between a beam lead carrying explosive and a land to which the lead is to be bonded, to detonate the explosive or an electron beam may be used to detonate lead and silver azide while nitrogen iodide may be detonated by gamma rays and neutron bombardment. The buffer layer carrying explosive may be used with the above methods of detonation. An integrated circuit device 121, Fig. 20, may have its contact pads 122 bonded to land areas 123 by explosive charges 124 on the upper surface of the device. Printed circuit substrates may be produced by stamping piece 131, Fig. 21, from aluminium film and bonding them to a glass or aluminium substrate 132 by detonating explosive 137 on a buffer layer 136. If the substrate is highly polished spacer pieces of gold or aluminium wire may be arranged between the pieces 131 and the substrate. A thick or thin film resistor, capacitor or inductor may be provided on a substrate providing a metallic pattern on one side of a buffer layer, providing a correspondingly patterned explosive charge on the other side of the buffer layer and detonating the charge. In the case of a capacitor a dielectric layer may be explosively bonded to the bonded metallic pattern and a further electrode similarly bonded to the dielectric layer.