The present invention relates to apparatus and methods for electric welding. More specifically, the present invention relates to methods and apparatus for electric spot-welding multiple spots from one face of a heat sensitive material. Even more specifically, the present invention relates to methods and apparatus for spot-welding multiple spots from one face thereby tacking a heat-fusible conductive sheet to a thin-film conductive layer on an electrically non-conductive heat-tolerant substrate.
Using a variety of techniques such as vapor deposition, sputter coating, photolithography, electroplating, etc., articles made of non-conductive materials, such as glass or ceramic, are increasingly produced with swig of one or more very thin metal layers. These thin film layers, purposed as electrical conductors, heat conductors, nucleation substrates for continued electroplating, etc., can also be used as anchorage substrates in a eutectic bonding operation.
For example of such a use, referring to
To improve thermal conductivity properties, the industry began moving away from a metal lid 2 and began using a ceramic lid 2′ that was made of an electrically non-conductive material. Although ceramic lid 2′ can be formed with a thin-film deposit of gold on the mating surface matching frame 7, the spot welding electrode arrays and methods used to tack frame 7 to metal lid 2 cannot spot weld frame 7 to ceramic lid 2′.
Since the industry is moving in the direction of utilizing ceramic lids in place of metal, it would be an important advance to have an apparatus and/or method for tacking a eutectic gold-tin frame material to the thin gold plating on the undersurface of a semiconductor package lid. In this regard it would be desirable to provide a method and apparatus for spot-welding a eutectic material to a thin-film on a non-conductive substrate.
It is an object of the present invention to overcome the problems of the prior art by providing a method and apparatus for spot-welding a eutectic material to a thin-film on a nonconductive substrate.
According to an embodiment of the invention, there is provided an electric welder for spot fusing a eutectic metal to a thin film electrical conductor on an electrically non-conductive substrate, including; at least one pair of an electrode, at least one the electrode having a terminal end that is tapered tangentially to a domed terminus, and the domed terminus having a radius sufficiently small to concentrate an electrical current to produce a heat cone and penetrate the eutectic metal and sufficiently large to prevent an intolerable damage to any of the eutectic metal, the thin film, and the substrate.
According to a feature of the invention, there is provided, for the above welder, that the substrate is a lid for an IC package made of ceramic or glass, the thin film is made substantially of gold, and the eutectic metal is a frame therefore made substantially of an alloy of 80% gold and 20% tin, and each the electrode is made of and alloy of copper tungsten.
According to a feature of the invention, there is provided, for the above welder, that the spot fusing is accomplished by pulsing the electrical current from a discharging capacitor through the electrode pair.
According to an embodiment of the invention, there is provided a method of using the welder for spot fusing a eutectic metal to a thin film electrical conductor on an electrically non-conductive substrate, including; placing the eutectic metal in registration contact with the thin film, pressing a pressure block against the eutectic metal, pressing at least one of the electrode pair of the welder into contact with the eutectic metal under sufficient pressure to displace a tiny bit of the eutectic metal against the thin film, pulsing an electrical current through the electrode pair of sufficient energy to cause a localized heating and melting of the eutectic metal, allowing the eutectic metal to cool and thereby solidify, and removing the electrode pair and the pressure block therefrom.
Briefly stated, the present invention includes an electric welder for spot fusing a eutectic solder matching a thin film deposition on an electrically non-conductive substrate. An example being a gold-tin solder fusing to a gold plated ceramic or glass surface. At least one pair of laterally displaced electrodes is resiliently engaged with the surface of the eutectic. The electrodes are tapered at the terminus to restrict the area of current flow. The engaging tip of the electrode is rounded tangentially to the taper and very slightly penetrates the surface of the eutectic. Once engaged the electrode pair is pulsed with sufficient current, from for example a capacitor discharge circuit, to create a local heat cone at the contact point sufficient to reach the eutectic point thereby locally fusing the eutectic to the plating.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.
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In this embodiment, the electrode array's intended use is to tack a frame 106 of eutectic solder to a thin metal film disposed on the undersurface of an IC package lid 107. A pod 108 aligns frame 106 laterally with lid 107 while electrode array head 100 advances. Referring to
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Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. For example it is considered within the scope of the invention to substitute other eutectic solder/metal matched combinations in place of the gold-tin eutectic/gold. Such metals as silver, palladium, lead, copper, platinum, etc and their eutectic match could be substituted for the gold.