DK144348B - METHOD OF MANUFACTURING ELECTRICAL RESISTANCE FROM A METAL ALLOY FILM - Google Patents

Description

o in 144348

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for producing electrical resistors from a thin sheet of metal or a metal alloy attached to an insulating substrate, which is of the kind specified in the preamble of claim 1.

Various methods of making resistors of the kind mentioned are known. In these known methods, openings and / or slits are formed through a sheet of metal or metal alloy in such a way that a whole consisting of electrical resistance filaments is obtained, which filaments have a small cross-sectional area and are interconnected. As a result, the effective length of the electric current path through the foil can be significantly increased, thus obtaining resistances exhibiting very large ohmic values per minute. unit area.

In a known method, a mask with apertures and / or slits corresponding to the contour of the resistance filaments to be provided in the thin film or film is applied to the film and this film or film is immersed in a chemical or electrochemical bath which is suitable for removing the metal alloy next to the mask's windows or tracks, see French Patent Specification No. 1,324,156.

By another method described in French Patent Application No. 7,607,889, filed on March 18, 1976, the film covered by an insulating mask is processed electrochemically.

The disadvantage of the method, which involves machining by chemical attack, is that filaments whose edges show irregularities. Because of these unevenness, it is impossible in the foil to form openings or slits whose edges are very close to one another, thereby compromising the stability of the resulting resistance due to electric field gradients which will tend to occur between uneven surfaces. 35 in the neighboring filament borders. This approach, on the other hand, has the advantage of being relatively easy to implement.

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In this method, a metal foil is applied to an insulating substrate and the whole is covered with a photosensitive film of a particular type. After illumination through a suitable mask and developing this membrane, it is all immersed in a chemical bath. When the machining process is complete, the photosensitive film is removed and the machined surface is covered with a protective and insulating layer of plastic material.

The disadvantage of the electrochemical treatment method 10 is that it requires a number of costly and complicated operations such as depositing a copper layer on the surface to be engraved, transferring the whole to another surface, a new transfer on the final insulating substrate, removal of the copper layer etc.

However, this method makes it possible to obtain a very smooth machined surface. The resulting filaments exhibit extremely even edges which are completely perpendicular to the machined surface. As a result, the resistors thus produced have extremely high ohmic values per minute. surface unit with extremely low spread in series production.

It is the object of the invention to overcome the disadvantages of the above-mentioned methods and to enable the production of resistors which exhibit very high ohmic values per hour.

25 surface unit, which can be completely reproduced by large-scale production while avoiding the number of complicated operations required by electrochemical processing.

This object is achieved by a method of the kind mentioned in the introduction, which according to the invention is characterized in that it proceeds as indicated in the characterizing part of claim 1.

In this way, it is possible to produce resistors with different values corresponding to the selected mesh thickness.

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Upon the ions collision with the metal foil and the mask, the kinetic energy of these ions is transferred to the atoms of the foil and the mask. If this energy is greater than that connecting the atoms, they leave the surface of the metal foil and the mesh. This phenomenon, which is still called cathodic pulverization, see, for example, G.K. Wehner: Advances in Electronics and Electron Physics, ed. Marton, p. 239, 1955, results in an erosion of the surface of the metal foil and the mask, inter alia, depending on the nature of the material of which the foil or the mask consists, the properties of the ions in question and the duration of the impact of the ion current.

In experiments, it has been found that this method allowed extremely narrow machining surfaces to be obtained and, as a result, resistances of high ohmic value per hour.

o surface unit, namely from 1 to 1.5 ΜΛ / cm, with a very small spread in large series fabrication.

The mask is preferably a photosensitive film comprising a layer of material on orthoquinone diazide derivative base, while the film is preferably made of nickel-chromium alloy.

This type of photosensitive film is commonly used in photogravure. The nickel-chromium alloys have the advantage that they have a very low temperature coefficient, which allows resistors to be obtained whose electrical properties vary only slightly depending on the temperature.

In addition, the ratio of the erosion rate of the aforementioned membrane to the aforementioned nickel-chromium alloy is particularly suitable for the process of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be explained in more detail with reference to the accompanying drawings, in which: FIG. 1 is a schematic and large-scale view of a cross-section through a metal foil applied to a substrate; FIG. 2 is a sectional view with a mask applied to the 35 of FIG. 1,

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FIG. 3 shows the mask applied to the one shown in FIG. 1 and 2, seen from above, FIG. 4 schematically shows an apparatus for producing an ion beam bundle for carrying out the method according to the invention; FIG. 5 is a cross-section through the metal foil attached to its support, following the process of the invention; FIG. 6 is a schematic view of the machining of the mask and metal film as a function of time during the execution of the method according to the invention; and FIG. 7 is a top view of a deformation measuring means.

FIG. 1 shows a sheet 1 of metal or of metal alloy attached to an insulating substrate 2, e.g. of 15 ceramics, using an adhesive layer 3.

The foil 1 has a thickness equal to some microns. The foil may also be applied directly to the substrate 2 in the form of a thin film provided by chemical or electrochemical deposition or by evaporation in vacuo.

In a first phase of the process, a mask 4 is provided which is provided with slots 5 on the foil 1, see fig. 2 and 3, whose edges 6 correspond to the outline of the electrical resistor (s) to be formed in the foil 1.

The resistor or resistors are formed by inserting the whole of the mask 4, the foil 1 and the substrate 2 into an ion beam bundle with a kinetic energy greater than the energy connecting the atoms which make up the mask 4 and the foil 1 of metal. or metal alloy.

The process can be carried out, for example, by means of the device shown in FIG. 4. This apparatus comprises a compartment 7 connected through a conduit 8 to a vacuum pump (not shown) capable of producing a vacuum of the order of 5 · 10 mm of mercury.

The apparatus further comprises an ionization and acceleration chamber 10 for the ion beam bundle 9. This chamber 10 is of the type described by Kaufman & Reader in UA348 5

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ARS Electrostatic Propulsion Conf. Monterey col. 960, Report No. 1374. The ionization of the gas, which in this example consists of argon supplied through a conduit 10a, is provided in a homogeneous magnetic field of some duusine Gauss formed by an induction coil 11 between a cylindrical anode 12 and an electron emitter filament 12a,

The ion beam bundle 9 preferably consists of positive argon ions with a kinetic energy between 1 and 2 keV and a 2 ion current density between 0.5 and 5 mA / cm. . The space 7 under vacuum 10 contains a support 13 whose surface 13a, which is exposed to the ion beam bundle 9 and perpendicular thereto, can receive one or more foils to be processed.

In the example shown, the support 13 is mounted in such a way that it can rotate about the axis of the beam 9. This rotation allows homogeneous machining of the metal foil (s) 1 exposed to the ion beam bundle 9.

In this example, the interior of the support 13 is otherwise flowed through a coolant 14 which ensures the cooling of the support 13.

The interaction between the ions of the radiation bundle 9 and the surfaces exposed to these ions by the mask 4 and the foil-1 causes a detachment of atoms which causes an erosion of the mask 4 and of the foil 1.

The material forming the mask 4, under the influence of the ion beam bundle 9, exhibits an erosion rate greater than the velocity of the material forming the film 1 to be processed.

The mask 4 preferably consists of a photosensitive film of the "photoresist" type consisting of a mixture of ortho-quinondiazide derivatives, e.g. the sulfochloride of 2.1 naphthoquinone-5-diazide, see United States Patent No. 3,046,120, and of phenol formaldehyde resin.

_J- 35 Under the influence of an A-ion beam bundle with an energy equal to 1 keV and a current density between 2 6

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At 0.5 and 0.6 mA / cm, the mask 4 of the above material undergoes an erosion at a rate of 4.5 Å / sec. This erosion rate is greater than the corresponding rate for the metals or alloys that may be suitable for the foil 1. If, for example, it consists of an alloy of Ni (80%) and Cr (20%), the erosion rate is under the conditions mentioned. equal to 2.7 Å / sec.

The mask 4 and the foil 1 are subjected to the influence of the ion beam bundle 9 at least until the mask 4 and 10 remove the metal next to the slits 5 of the mask 4. This is possible because the erosion rate of the mask 4 is greater than that of the foil 1. Thus, it is avoided to have to remove the mask 4 in a separate step as in the prior art chemical and electrochemical methods.

It is preferred to continue the action of the ion beam bundle 9 until the machined film 1 exhibits the intended ohmic value.

FIG. 5 shows the result of machining by means of the ion beam band 9. The mask 4 is completely removed and there are metal filaments 1a with rounded edges and separated by slits 15 having a width 1 ^ greater than the original width 1g of the slits 5 of the mask 4 .

FIG. 6 shows the evolution of the mask 4 and the metal foil 1's erosion as a function of time under the influence of the ion beam bundle 9. In the following, the numerical results of the experiments on which this figure is based will be given.

Example 1

Thickness e ^ of the mask 4: 1.3 microns thickness of the foil 1 (Ni-Cr): 2.5 microns

ion beam bundle 9: A +, energy = 1 keV

2 current density: 0.6 mA / cm.

35 Lines A, B, C, D and E correspond to the erosion fronts that have occurred at the end of the times given below.

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Table I

line time (see) A 676 B 1000 5 C 2955 (t ^ D 5000 E 9200 t ^ = the time needed for complete removal of the mask 4 10 t2 = the time needed to obtain a complete machining of the film 1 , i.e. to completely remove the metal from the original slots 5 of the mask 4.

At the expiration of time t 2, the resulting metal filaments 1a in this example exhibit a thickness equal to approx.

1 micron.

Examples 2 and 3 For comparison, the following are given the values of t ^, t2 and e ^ obtained under the same conditions as in the previous case, but starting from a mask 4 whose original thickness e ^ was equal to 2, 3 microns, respectively.

Table II

The thickness of the mesh 4 of the mesh 4 is the thickness of the mesh e3 2 microns 4545 9200 1.5 microns 3 microns 6818 9200 1.9 microns

It can be seen from the results given in Tables I and II above that by using meshes 4 with increasing thicknesses e ^ at the expiration of equal lengths t2 35 filaments 1a with increasing thicknesses are obtained. This peculiarity is remarkable in that it makes it possible to use without difficulty the method of the invention for fabricating resistors of different ohmic values.

Thus, in an advantageous embodiment, foils 1 are made of metals or of alloys of equal thickness, and on these are applied masks 4 with slots 5 which have the same shape, but where the thicknesses e e vary depending on the amount of metal. to be removed from the foil, ie. of the thickness e ^ .man will obtain for the filaments 1a.

One can then subject a whole series of foils 1 attached to their insulating substrate 2 and covered by their meshes 4 of different thicknesses to the influence of an ion beam bundle 9 for a predetermined period of time.

In the following, other examples of implementation of the method will be provided.

Example 4 A foil 1 made of an alloy of Ni (80%) and Cr (20%) and having a thickness equal to 2.5 microns is used, adhered to a ceramic plate. On the nickel-chrome foil is applied a mask "photoresist" type 4, the thickness e of which is equal to 1.5 microns, and which is provided with slots 5, whose width 1q is equal to 6 microns, these slots 5 mutually is at a distance L equal to 14 microns, see fig. 2. It is all placed under a beam bundle of A ions (positive argon ions) with a kinetic energy equal to 2 keV and with an ionic current density of 1 to 1.2 mA / cm.

In this way, an electrical resistance of shape is obtained as a square with sides of 5.4 mm consisting of 204 parallel filaments 1a, see fig. 5, having a thickness e ^ of 1 micron and a width 1 ^ of 11 microns separated by wear 15, the width of which is equal to 9 microns.

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At the end of the work, the metal filaments 1a are protected and electrically insulated with a plastic material coating not shown, such as an epoxy resin.

The ohmic value of the resulting resistance equals 5 to 130 kilo-ohms. By comparison, by subjecting one to the above identical foil 1 for electrochemical treatment, one obtains an ohmic value not exceeding 45 kilo ohms.

Example 5

Proceed as in Example 4, starting with a mask 4 having a thickness e ^ equal to 3 microns, while the width 1 ^ and the number of slots 5 correspond to the values given in Example 4. A resistor is obtained whose ohmic value is equal to 90 kg ohm.

Further, the ohmic values of the electrical resistances obtained in Examples 4 and 5 can be increased by continuing the action of the ion beam bundle 9 beyond the period t2 necessary to completely remove the metal foil 1 from the original slots 5. in the mask 4.

Example 6

The ohmic value of the electrical resistance obtained in Example 1 will be adjusted to 135 kilo-ohms.

To this end, the resistor is connected to a measuring bridge and the ion beam bundle 9 is terminated when the measuring bridge shows that the resistance is equal to 135 kilo-ohms. In the example in question, the duration of the supplementary activity of the ion beam bundle 30 is of the order of 15 to 18 seconds.

The foregoing descriptions make it clear that the process according to the invention offers the following advantages: - its implementation is very fast, since at one time several hundred resistors can be treated with the ion beam bundle and the entire duration of the engraving does not exceed a few hours, execution is simple as it involves only a very small number of steps - it can be used for machining a much larger number of metals or alloys than the known chemical and electrochemical machining methods, thereby making the process applicable to many different resistances, - it can be used for series production of resistors with different ohmic values without modification of other parameters of the method than the thickness of the mask 4.

The electrical resistances produced by the method differ from those previously known in that the metal filaments 1a, see FIG. 5 shows a cross section whose profile is rounded and convex, with the convexity facing outwardly from the resistor.

In experiments, it has been found that such resistances had ohmic values per day. surface unit that clearly exceeded the corresponding values of resistors provided by the known methods. This result can be explained partly because the slits 15 provided at the end of the ion bombardment are larger than the original slits of the mask 4, and partly because the cross-section of the filaments 1a is a rounded and convex profile.

The method can further be used for the fabrication of thermometric probes and deformation measuring means.

FIG. 7 shows an embodiment of a strain gauge made by the method, as seen from above.

This deformation measuring means comprises one or more electrical resistors 20 provided by engraving a sheet of metal or metal alloy attached to an insulating substrate 21 consisting of a ceramic or glass plate. The resistor (s) 20 35 consists of fine parallel filaments 22 and 22a, whose ends 23 are interconnected to form a curved base V.

11 144348, the total length of which is much greater than the dimensions of the insulating substrate. In the example shown, the filaments 22a located along the two opposite sides of the insulating substrate 21 have thickened ends 24 which serve to connect the 5 'deformation measuring means to the outer electrical circuit. To fabricate such a deformation measuring means, proceed as follows: - a metal foil or a suitable alloy is applied to the insulating substrate 21,.

10 - a mask consisting of a photosensitive film is placed on this film, the latter being exposed to radiation, and this film is developed in such a way as to obtain slots and / or openings corresponding to the pattern to be formed in the film. of metal or alloy, and subject the mask thus obtained and the foil of metal or of alloy to the effect of an ion beam bundle until the metal adjacent to the slots and / or openings is removed.

20 An example of the method used in the manufacture of a deformation measuring means is given below.

Example 7 A foil consisting of an alloy is used

Nine (80%) and Cr (20%) and with a thickness equal to 2.5 microns, which film is adhered to a ceramic plate 21. A light-sensitive mask with slots and openings corresponding to the outline to be engraved is placed on the foil.

This whole is subjected to bombardment with an ion beam bundle of A +, ie. positive argon ions, with a kinetic energy equal to 1 keV, whereby the A + ion current density is of the order of 1 mA / cm.

Under these conditions, the mask erosion rate is between 4 and 5 Å / sec and the nickel chromium foil is between 2.5 and 3 Å / sec.

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In this way, a deformation measuring means of rectangular shape is obtained having a length equal to 14 mm and a width equal to 7 mm. At the end of the operation, the machined film is electrically insulated and protected against mechanical overload by a coating of plastic material such as an epoxy resin.

In the manufacture of thermometric probes, the above procedure is employed, preferably using as a starting material a sheet of metal or alloy for which the temperature coefficient is a substantially linear function of temperature between - 200 ° C and + 600 ° e. This requirement is met using platinum, nickel and platinum-tungsten alloys. If platinum and platinum-tungsten alloys are used, the thermometric probe can be used up to temperatures of 2000 ° C.

In the following, an example will be given of the method's use for the preparation of a thermometric probe.

Example 8

Proceed as described in Example 7, using as a starting material a platinum foil whose thickness is equal to 2.5 or 4 microns. With this method, a thermometric probe with a resistance equal to approx. 60 kg ohm / cm.

Experience has shown that the method made it possible to obtain thermometric probes and deformation measuring means with ohmic values per minute. surface unit greater than the corresponding values for measuring means or probes 30 provided by the prior art methods. Thus, thermometric probes and deformation measuring means with greatly reduced dimensions can be obtained, which is of considerable interest in certain applications in electronics.

35 Since the process does not depend on the metal or the alloy that constitutes the foil to be machined, this method further makes it possible to use metals

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Or alloys which are not affected by the usual chemical or electrochemical reagents, but which are particularly well suited for the manufacture of thermometric probes or deformation measuring means.