Arrangement and method for mechanical and electrical contact with the heating wire of a thermal radiation source made of refractory metal for semiconductor and microsystems technology

Abstract

The invention relates to an arrangement for mechanical and electrical contacting of an electric heating wire of a heat radiation source, comprising a contact surface of the electric heating wire made of a refractory metal, having at least one planar contactable joint surface, a contact surface in contact with the electric heating wire, a contact element connecting the electric heating wire with the contact surface, and a method for producing the contact arrangement according to the invention. The task of the invention is to provide a reliable and long-term stable mechanical and electrical contacting of an electric heating wire made of a refractory metal, which is solved by the design that the planar joint surface of the electric heating wire has at least two perforations and / or at least two recesses are configured on the surrounding edge of the joint surface of the electric heating wire, wherein the contact element is connected with the contact surface material-bonding at the location of the perforations and / or recesses and by the contact element configured as a flange-like structure above the contact surface of the electric heating wire at the location of the perforations and / or recesses not only forms an electrical connection but also a mechanical connection with the electric heating wire.

Description

TECHNICAL FIELD

[0001] The invention relates to an arrangement for mechanical and electrical contact with an electrically heated filament of a heat radiation source, according to the preamble of claim 1, wherein the arrangement of the electrically heated filament made of refractory metal has at least one planarly contactable joint surface, which comprises a contact surface in contact with the electrically heated filament and a contact element connecting the electrically heated filament with the contact surface.

[0002] The invention likewise relates to a method for producing a contact according to the invention. BACKGROUND

[0003] The radiation power of a heat radiation source is proportional to the fourth power of its absolute temperature and is described by the Stefan-Boltzmann law. Therefore, in order to achieve a high radiation output, the electrically heated filament of a heat radiation source must have the highest possible temperature. This requires materials with very high melting points. Particularly suitable for this are refractory metals, i.e. non-noble metals with a high melting point, such as tungsten, tantalum or molybdenum.

[0004] The most well-known heat radiation source is the incandescent lamp, in which a tungsten filament is heated by an electric current and emits light. Depending on the design, the temperature of the electrically heated filament is approximately 1500°C to 3000°C. Due to the high temperature and the electric current at the contact point, material transfer can occur here. The non-noble metal then creeps along the electrically heated filament and chemically reacts with it. This leads to embrittlement and the formation of potential breaking points, which reduce the service life of the heat radiation source. In particular when switching on or off, these embrittlements can break. Therefore, the materials for the two plug-in partners (electrically heated filament and contact) must be carefully selected. For example, US 2145186 A discloses a mechanical fixation of the filament and the internal power supply line in a sealed piston of an incandescent lamp.

[0005] Refractory metals are relatively resistant to corrosion at room temperature due to passivation. However, at high temperatures they readily react with many non-metals and gases, which is why there are high demands on the purity and gas tightness of the housing and on the electrical contact. A secure and long-term stable electrical contact of the electrically heated filament at high temperatures is achieved by a welded connection, usually by so-called resistance spot welding. In this process, the metals are joined together because the atoms of the two spliced parts chemically react with each other or metallurgically and form a firm bond. Exemplary ways of welding between the electrically heated filament and the power supply lead are disclosed in US 1477618 A, DE 102004061736 A1, DE 2200736 A and DE 735789 A. Likewise, US 4370589 A discloses a way of welding between the filament of an electric incandescent lamp and the power supply lead, wherein the inner end of the power supply lead is configured toothed and welded onto the end of the electrically heated filament, so that the electrically heated filament and the power supply lead are fused to each other at multiple locations and these places provide a firm and reliable electrical connection.

[0006] However, resistance spot welding does not work well for all materials to be connected together. The reason is the physical properties and the interaction with the electrode material. The ideal material properties for resistance spot welding are:

[0007] • the same or similar melting point

[0008] • low electrical conductivity

[0009] • low thermal conductivity

[0010] • high ductility (hot deformability).

[0011] These properties are rarely met in real welding tasks. Hard and brittle materials, such as refractory metals, are also prone to breakage during welding and cooling. This affects the quality and reliability of the electrical contact.

[0012] In addition, welding is not a standard process in microelectronics and microsystems technology. Common methods are, for example, wire bonding and flip-chip bonding.

[0013] In wire bonding, the contact of a component 5 is connected to an electrical contact 4 of another component or a housing by means of a thin metal wire (bonding wire), see Figures 1 and 2. Gold, aluminum or copper are usually used as bonding material. A very common wire bonding process is the so-called ball wedge bonding. Here, the end of the bonding wire 2, which protrudes outward from the capillary 1 of the wire bonder, is melted, so that a ball 3 is formed by the surface tension. This ball 3 is bonded to the contact surface 4 by means of pressure, heat and ultrasound and forms a so-called ball bond 6. In ball bonding, the bonding wire 2 is pulled towards the other contact surface 4 and is bonded, see Figure 2. However, a special form of ball wedge bonding is missing in the so-called ball bonding, as shown in Figure 1. Here, after the first ball bond 6 has been completed, the wire clamp at the capillary 1 is closed and when the capillary 1 is activated, the bonding wire 2 is cut directly at the bonded ball. A spherical protrusion, also called stud bump 7, is thus created on the contact surface 4. This process is mainly used for flip-chip assembly. DE 19 48 969 A describes a method for connecting a heating wire to a metal lead, in which a metal bead is heated to a plastic or semi-plastic state during the pressing of the metal bead against the lead and the heating wire thereon, in the process an intermetallic or metallurgical connection is formed by diffusion at the interface between the metal bead and the lead.

[0014] Aluminum is not suitable for contact with heating wires made of refractory metals, as it is far removed from the noble metals and has a very low melting point.

[0015] The noble metal "gold" is generally used in microelectronic and microsystem processes as conductor tracks, in particular as bond wires, and for contact surfaces, since it has excellent electro-thermal properties, is very easy to process, has high corrosion resistance and is easy to solder. However, due to the high electrical and thermal conductivity, the soldering suitability of gold is limited. With refractory metals it is not possible to achieve reliable and long-term stable soldering.

[0016] In recent years, copper wire bonding has begun to be accepted, mainly due to its enormous cost advantage over gold wire, as well as other advantages. Its direct current resistance and thermal conductivity are superior to those of gold wire. In addition, copper has higher mechanical stability and better contact reliability at high temperatures. However, copper begins to oxidize rapidly at room temperature, which is a disadvantage. If the copper oxide layer is too thick, it can no longer be bonded, since the material becomes too hard. In addition, the end of the bond wire can no longer be melted into a ball, which is necessary for the formation of stud bumps. Therefore, it is important to protect the copper wire from oxidation. This requires appropriate oxygen-free storage and handling of the copper bond wire. Like gold, copper cannot be reliably and long-term stably soldered to refractory metals.

[0017] Even with the described, known contact methods for wire bonding of microelectronic components, such as refractory metals, it is not possible to reliably and long-term stably directly contact hard and brittle materials such as gold, copper or aluminum wires. SUMMARY

[0018] It is therefore the task of the present invention to provide a reliable and long-term stable mechanical and electrical contact to an electrically hot wire made of a refractory metal, which can be achieved with common microelectronic and microsystem processes and thus easily integrated, for example, into a micro-opto-electro-mechanical system (MOEMS), and which can be realized highly automated.

[0019] This task is solved by an arrangement according to the independent claim for an arrangement for the mechanical and electrical contact of an electrically hot wire of a heat radiation source. According to the invention, the flat joint surface of the electrically hot wire has at least two perforations and / or at least two recesses are configured on the surrounding edge of the joint surface of the electrically hot wire, wherein the contact element is connected to the contact surface material-bonding at the location of the perforations and / or recesses and forms not only an electrical connection but also a mechanical connection to the electrically hot wire by configuring the contact element as a flange-like structure above the contact surface of the electrically hot wire at the location of the perforations and / or recesses. The flat joint surface is to be understood as the part of the electrically hot wire which lies flat on the contact surface, wherein the extension of the joint surface in this plane is significantly greater than its thickness.

[0020] It is particularly advantageous to clamp the heating wire in the joint surface with a hole and / or recess of the heating wire to the flat contact surface with a wire bond ball, the so-called stud bump, and to fasten it thereto. The connection thus formed is not only reliably electrically connected but also reliably mechanically connected to the contact surface of the heating wire made of refractory metal. By combining the modification of the flat joint surface of the heating wire with the well-known ball bonding process, it is possible to reliably and long-term stably contact the refractory metal with mature and highly automated semiconductor and microsystem technology at low cost expenditure, which has not been possible so far or only with high cost expenditure.

[0021] The wire bond ball, which is referred to as stud bump in semiconductor and microsystem technology, forms a connection with the contact surface by pressure, heat and ultrasound, the bond ball being a flattened ball when viewed in cross section. This flange-like flattened design is used in the arrangement according to the invention to mechanically clamp the joint surface of the heating wire to the contact surface, similar to a rivet connection. The electrical connection is also made by the planar contact of the joint surface of the heating wire and the stud bump in the hole and / or recess on the edge of the joint surface of the heating wire. During operation of the heat radiation source with the contact design according to the invention, thermal expansion of the heating wire and the contact element additionally occurs, so that the contact resistance between the joint surface of the heating wire and the contact surface approaches zero.

[0022] The advantage compared to previously known contact methods with refractory metals is, among others, that by the arrangement according to the invention, embrittlement of the contact point of the refractory metal does not occur, nor does material transfer, so that the service life of the construction part with the contact point made of refractory metal can be significantly increased. This contact form can be easily realized with mature and highly automated semiconductor and microsystem technology and can therefore be easily integrated into the manufacturing process of micro-opto-electro-mechanical systems (MOEMS) that have a need for contact with refractory metals.

[0023] In one embodiment of the arrangement according to the invention, the hole is circular, triangular (n = 3), square (n = 4) and / or n-angled. n here is a natural number greater than 2. Depending on the size of the stud bump, which depends on the diameter of the bond wire and the process parameters during wire bonding, the mechanical and electrical contact can be optimized thereby. Typical bond wire diameters are in the range of (10...50) pm. This results in a diameter of the stud bump that is typically less than 100 pm. The diameter of the hole and the recess must be smaller than the diameter of the stud bump in order to be able to clamp reliably.

[0024] In another embodiment of the arrangement according to the application, the recesses are triangular (n = 3), square (n = 4), trapezoidal (n = 2), arcuate and / or n- sided. Here n is a natural number greater than 2. Depending on the dimensions of the stud bumps, which depend on the diameter of the bonding wire and the process parameters during wire bonding, the mechanical and electrical contact can thereby be optimized.

[0025] The joint surface of the heating wire can have perforations or recesses or both, which can be freely combined in shape.

[0026] In another design of the contact according to the application, the contact surface and the contact element are preferably made of gold and copper. Gold and copper have excellent electrical and thermal properties and can be processed well. Gold in particular also has high corrosion resistance and is easy to solder.

[0027] In another design of the contact according to the application, the refractory metal of the heating wire is tungsten or tantalum. These materials are preferably used in heat radiation sources with high radiation output, since they have a very high melting point.

[0028] In a design of the contact according to the application, the heating wire can be heated at temperatures greater than 700°C without a chemical reaction occurring between the heating wire and the contact point. The contact point refers to the point at which the contact element is connected to the contact surface in combination, where a mechanical and electrical connection is established between the joint surface of the heating wire and the contact surface by means of the perforations and / or recesses. This is only possible by modifying the joint surface of the heating wire on the one hand and the contact element in combination with the underlying contact surface at the location of the perforations and / or recesses on the other hand. Since the heating wire made of refractory metal does not form a chemical connection with the contact surface, at very high temperatures above 700°C no more material flow or material transfer occurs between the refractory metal and the material of the contact element. This prevents the creeping of the non-noble metal along the heating wire and the chemical reaction with it. No more breakage or the formation of potential breaking points that reduce the service life of the heat radiation source occurs.

[0029] The task of the application is also solved by a method for producing an arrangement for the mechanical and electrical contact of a heating wire for a heat radiation source according to claims 1 to 6, wherein the contact element is applied to the contact surface by means of wire bonding at the location of the perforations and / or recesses and the contact element directly on the flange-like protrusion above the joint surface of the heating wire at the location of the perforations or recesses is broken off.

[0030] The arrangement according to the application and its production are suitable for and designed for use in semiconductor and microsystem technology. BRIEF DESCRIPTION OF DRAWINGS

[0031] The application will be explained in more detail by means of examples. The drawings show:

[0032] Fig. 1 shows the ball bonding method known from flip chip assemblies for producing ball-shaped bumps, so-called stud bumps, on planar contact surfaces;

[0033] Fig. 2 shows the form of wire bond contacts in microelectronic components known from the prior art;

[0034] Figure 3 One embodiment of a heating wire according to the application with a joint surface having perforations: (a) circular perforations, (b) triangular perforations, (c) rectangular perforations, (d) n- sided perforations;

[0035] Figure 4 One embodiment of a heating wire according to the application with a joint surface having recesses: (a) triangular recesses, (b) rectangular recesses, (c) trapezoidal recesses, (d) combinations of different recesses;

[0036] Figure 5 One embodiment of a heating wire according to the application made of refractory metal with a joint surface having perforations and recesses: (a) circular perforations and trapezoidal recesses, (b) circular perforations and triangular recesses;

[0037] Figure 6 One embodiment of a heating wire according to the application made of refractory metal with a joint surface having perforations and recesses: (a) circular perforations and trapezoidal recesses, (b) circular perforations and triangular recesses;

[0038] Figure 7 Cross section of a heating wire according to the application with a joint surface having a perforation and two recesses on the contact surface. DETAILED DESCRIPTION

[0039] Figure 3 One embodiment of a heating wire according to the application with a joint surface 10 having perforations of different forms is shown. Depending on the dimensions of the stud bump 7, i.e. the contact element, which depend on the diameter of the bond wire and the process parameters during wire bonding, the mechanical and electrical contact can be optimized.

[0040] Figure 4 One embodiment of a heating wire according to the application with a joint surface 10 having perforations of different forms is shown. Depending on the dimensions of the stud bump 7, i.e. the contact element, which depend on the diameter of the bond wire and the process parameters during wire bonding, the mechanical and electrical contact can be optimized.

[0041] Figure 5A preferred embodiment of a contact surface 10 of an electrical heating wire according to the application with different forms of perforations 11 and recesses 17 is shown. Since the diameter of the bond wire cannot be reduced at will, the combination of perforations 11 and recesses 17 is advantageous, especially for the case of very small areas of the contact points, since a greater number of contact points can be designed. By placing the first stud bumps 7 into the perforations 11, the electrical heating wire is fixed and prevented from slipping. The further stud bumps 7 in the recesses 17 provide the necessary mechanical stability and good electrical contact.

[0042] Figure 6 A preferred embodiment of a contact according to the application between a structured contact surface 10 of an electrical heating wire made of refractory metal and a bonded stud bump 7 is shown. It is particularly advantageous that the perforations 11 and Z or recesses 17 in the contact surface 10 of the electrical heating wire serve to clamp the electrical heating wire on the flat contact surface 4 of the wire bond ball, the stud bump 7, and thus to secure it. The connection thus formed not only electrically connects the electrical heating wire made of refractory metal on the contact surface 4, but also reliably mechanically connects it. This connection is long-term stable, reliable and can be produced without great effort.

[0043] The stud bump 7 made of, for example, gold or copper forms a material-bonding connection with the contact surface 4 also made of, for example, gold or copper, wherein the bonded bond ball 3 is a flattened ball 18 ( Figure 7 ) in cross section, the bond wire end 19 of which is broken off. The flange-like flattened structure 18 serves to mechanically clamp the contact surface 10 of the electrical heating wire to the contact surface 4, similar to a rivet connection. An electrical connection is also produced by the planar contact of the contact surface 10 of the electrical heating wire and the stud bump 7 in the perforations 11 and / or recesses 17 on the edge of the contact surface 10 of the electrical heating wire. During operation of the heat radiation source with the contact design according to the application, thermal expansion of the electrical heating wire and the contact element, for example the gold wire, also additionally occurs, so that the contact resistance between the contact surface 10 of the electrical heating wire and the contact surface 4 approaches zero.

[0044] The advantage compared to previously known contact methods with refractory metals is, among others, that with the arrangement according to the application no embrittlement of the contact site or material transfer occurs, so that the service life of the construction part with the contact site made of refractory metal can be significantly increased. No contact site passivation or the like occurs.

[0045] List of reference signs

[0046] 1 Capillary of a wire bonder

[0047] 2 Bond wire

[0048] 3 Ball

[0049] 4 contact surface, electrical contact

[0050] 5 construction part

[0051] 7 stud bump

[0052] 8 substrate

[0053] 9 wedge bonding

[0054] 10 contact surface of the heating wire

[0055] 11 circular perforation

[0056] 12 triangular perforation

[0057] 13 rectangular perforation

[0058] 14 n-gon perforation

[0059] 15 triangular recess

[0060] 16 rectangular recess

[0061] 17 trapezoidal recess

[0062] 18 flattened sphere

[0063] 19 broken bonding wire

Claims

1. Arrangement for mechanical and electrical contact of an electrical heating wire of a heat radiation source, comprising a contact element (7) made of a refractory metal, having at least one planar contact surface (10), a contact surface (4) for contact with the electrical heating wire, a contact element (7) for connecting the electrical heating wire to the contact surface (4), characterized in that The flat joint surface (10) of the heating wire has at least two perforations (11, 12, 13, 14) and / or at least two recesses (15, 16, 17) are configured on the surrounding edge of the joint surface (10) of the heating wire, wherein the contact element (7) is materially bonded to the contact surface (4) at the location of the perforations (11, 12, 13, 14) and / or recesses (15, 16, 17) and is designed as a flange-like structure (18) above the joint surface (10) of the heating wire at the location of the perforations (11, 12, 13, 14) and / or recesses (15, 16, 17) not only to form an electrical connection but also a mechanical connection to the heating wire.

2. Arrangement for mechanical and electrical contact of an electric heating wire of a heat radiation source according to claim 1, characterized in that The perforations are configured as circular (11) and / or n-sided (14), wherein n is a natural number greater than 2.

3. Arrangement for mechanical and electrical contact of an electric heating wire of a heat radiation source according to claim 1, characterized in that The recesses are configured as arc-shaped and / or n-sided, wherein n is a natural number greater than 2.

4. Arrangement for mechanical and electrical contact of an electric heating wire of a heat radiation source according to claim 1, characterized in that The contact surface (4) and the contact element (7) are made of gold and / or copper.

5. Arrangement for mechanical and electrical contact of an electric heating wire of a heat radiation source according to claim 1, characterized in that The refractory metal of the heating wire is tungsten or tantalum.

6. Arrangement for mechanical and electrical contact of an electric heating wire of a heat radiation source according to claim 1, characterized in that The heating wire can be heated beyond 700°C without a chemical reaction between the heating wire and the contact site.

7. Method for manufacturing an arrangement of mechanical and electrical contacts for an electrical heating wire for a heat radiation source according to any one of claims 1 to 6, wherein, The contact element (7) is applied to the contact surface (4) by means of wire bonding at the location of the perforations (11, 12, 13, 14) and / or recesses (15, 16, 17) and is broken at the flange-like protrusion directly above the joint surface (10) of the heating wire at the location of the perforations or recesses.

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