FR2622042A1 - Process for the manufacture of electrical resistors from at least one metal sheet attached onto an insulating support - Google Patents

Abstract

The process is of the type consisting in etching by ion bombardment a unit consisting of a mask 4, a metal sheet 3 to be etched and an insulating support 2, and it is characterised in that it consists in employing as mask 4 a stationary metal mask which can be used only once, in arranging on the said mask 4 a positive photosensitive layer 5 which is covered with a removable mask 6 carrying the design of the component to be etched on the said metal sheet, the said design of the component being transferred in the form of image onto the said positive photosensitive layer by the action of a luminous source, and in then chemically etching the said image on the said stationary mask. Applications especially to the manufacture of electrical resistors, strain gauges and other temperature resistance probes.

Description

PROCESS FOR THE MANUFACTURE OF ELECTRIC RESISTORS FROM
BY MEANS OF MY IBTAL SHEET FIXED ON AN INSULATING SUPPORT
The present invention relates to a process for the manufacture of electrical resistors1 in particular for
Strain gauges and Zou of temperature resistance probes d2, from at least one fixed metal sheet * on an insulating support.

 Various methods implementing an etching of a metal sheet either by electrochemical machining or ion bombardment have already been proposed.

 An example of electrochemical etching is given in French patent 1 324 156. Such methods are limited in their use due to the fact that it is very difficult to produce very fine etchings. The resistances obtained according to this type of process having low nominal values, n1 not exceeding 3000 ohms.

 Ion beam etching is described in French patents 2,354,617, 2,372,499, 2,111 5'1 and in German application 2,144 6 = 6. The ion beam process consists of fixing a metal sheet on an insulating support.

applying to said metallic sheet a mask comprising the outline of the electrical resistant circuit to be etched, and subjecting the support-metallic sheet-mask assembly to a beam of ions of an inert gas so as to tear off the parts of the sheet metal not protected by the mask.

Of course, the exposure time under the ion beam essentially depends on the time necessary for the complete removal of the metal not protected by the mask.

 The improvement proposed in French Patent 2,354,617 consists in using a metal sheet having identical thicknesses for a whole series of desired ohmic values, and a mask having grooves of identical configurations but whose thicknesses vary according to the quantity of metal. to be removed, the mask erosion speed being greater than that of the metal sheet so that said mask is completely eliminated by the action of the ion beam.

 However, such a method requires the use of a relatively thick and sometimes even very thick photosensitive resin layer, which tends to reinforce the defects on the final product.

 The present invention aims to remedy the aforementioned drawbacks and relates to a method of manufacturing electrical resistors, in which a fixed metal mask known as "lost" is used which turns out to be much more resistant and more precise than photosensitive resins. A metal mask which is used only once is called a "lost" metal mask, unlike traditional metal masks which are used several times.

 The present invention relates to a method of manufacturing electrical resistors, of the type consisting in etching by ion bombardment an assembly consisting of a mask, a metal sheet to be etched and an insulating support and it is characterized in that it consists in using as a mask a fixed mask, to have on said mask a positive photosensitive layer which is covered by a removable mask carrying the design of the component to be etched on said metal sheet, said design of the component being transferred in the form of an image onto said positive photosensitive layer by the action of a light source, then chemically etching said image on said mask.

Other advantages and characteristics will appear on reading the description of a preferred embodiment of the invention, as well as the appended drawings in which
Figure 1 is a schematic cross-sectional view of a stack of elements from which the resistors are made according to the method of the present invention.

 Figures 2 to 6 are schematic sectional views of the elements shown in Figure 1 but at different stages of the method according to the invention.

 The method according to the invention consists in producing a stack comprising an insulating support, a metal sheet to be etched, a fixed mask, a layer of positive photosensitive resin and a removable mask comprising the components to be etched on said metal sheet; exposing said stack to the action of a light source, so as to completely eliminate the parts of the photosensitive resin layer not comprising the images of the components transferred onto said photosensitive resin layer, to chemically etch said images only on the fixed mask; exposing the rest of the stack to ion bombardment so as to transfer the images of the fixed mask onto said metal sheet to be etched.

 In other operations, the board obtained is cut to have gauges or resistances or unit probes which are then adjusted to the nominal value either by mechanical polishing with a neutral abrasive or by laser.

 We will now describe in detail the different steps of the method according to the invention.

 In a first step, we draw in a known manner and on a large scale the drawing of the components that it is desired to obtain, such as resistors, strain gauges and other probes. Then we reduce this drawing to the unit scale and we photograph the unit drawing a number of times on a removable mask which can be a film, a thin photographic glass plate covered with gelatin or suitable metal such as chromium. Therefore, said removable mask has several times the basic unitary design.

 In another step which may be carried out before, after or simultaneously with the production of the removable mask, a stack 1 is produced comprising an insulating support 2 on which a metal sheet 3 is bonded or fixed by any suitable means in which the components will be produced , a fixed mask 4 deposited by evaporation on the metal sheet 3, a layer of positive photosensitive resin 5, disposed on said fixed mask 4, and finally the removable mask 6 with its unitary drawings.

 The insulating support 2 can be a flexible or rigid plastic film, or an insulator or ceramic or glass, or any other product suitable in the technique considered.

 The metal sheet 3 has a thickness which is a function of the nature of the component to be etched and of the final value of the component once it has been manufactured. The material used for the metallic foil can be copper, balco, nickel, chromium nickel, constantan, platinum or a platinum alloy, and in general any metal or alloy having extensometric characteristics or sensitivity. at temperature.

 The fixed mask 4 can be, for example chrome or another metal or alloy compatible with the material used for the metal sheet 3. The thickness of the fixed mask 4 is at least equal to that of the metal sheet 3.

 The layer of positive photosensitive resin 5 is of the type marketed under the reference AZ 1400 and it is spread on the fixed mask 4 by centrifugation at a speed of rotation of the order of 4,000 rpm. The subassembly consisting of the support 2, the metal sheet 3, the fixed mask 4 and the photosensitive resin 5 is subjected to a go annealing. C for thirty minutes so as to obtain a homogeneous layer capable of receiving and preserving the images of the components.

The stack 1 is subjected to the action of a light source 7 for twenty seconds, in an appropriate room, and capable of transferring the design of the components of the removable mask 6 to the positive photosensitive resin 5 which then includes the images of said components . Then developed in a bath which is an aqueous solution of the type sold by the
SHIPLEY company under the reference "AZ 351".

 In another step, annealing is carried out for thirty minutes at ioo C to obtain a sub-assembly (8) as shown in FIG. 2.

 The subassembly 8 is subjected to chemical etching in an etching bath such as L'KETCH 5 sold by the company MIT SOLINGEN, for approximately one minute 45 seconds. The quality of the engraving obtained is optionally checked under a microscope.

The sub-assembly 9 shown in FIG. 3 always includes the support 2, the metal sheet 3, parts 4a of the fixed mask 4 and parts 5a of the photosensitive resin 5, which have not been attacked by the chemical etching which ultimately attacked all the parts of the fixed mask between the parts 4a without having attacked the metal sheet 3.

 The parts 5a of the positive photosensitive resin 5 are removed by immersing the sub-assembly 9 twice in a stripping bath for one minute so as to obtain a sub-assembly 10 as shown in FIG. 4 and comprising the support 2, the sheet metal 3 and the remaining parts of the fixed mask 4.

The l0est sub-assembly is exposed to ion bombardment in a KAUFKANN type device in which the operating conditions are as follows
cathode: 5a
gas: argon
discharge current: 12 A
magnetic field supply: 5 A
ion extractor: 4 W 4oe V: 10 mA
accelerator: 1,200 V; 0.95 mA
etching chamber pressure: 5.10--5- torr
discharge chamber pressure: 2.10-4 torr
lifting time: 2 h 45 mm.

 The action of the ion bombardment has the result of eliminating all the parts of the metal sheet 3 which are not below the fixed mask 4 remaining while allowing the engraving of the images of said mask on the metal sheet 3 and this, thanks at the lower or equal erosion speed of the mask than that of the metal foil 3 - (Figure 5).

 The residues of the mask 4a are then removed in a cleaning bath so as to obtain a sub-assembly 11 which comprises the support 2 and the engraved parts 3a of the metal sheet 31 (FIG. 6).

 The sub-assembly 11 is then subjected to cutting and adjustment as indicated above.

 Of course, the invention is in no way limited to the embodiments described and shown, it is capable of numerous variants accessible to those skilled in the art according to the applications envisaged without departing from the scope of the invention.

Claims (7)

 1. A method of manufacturing electrical resistors, of the type consisting in etching by ion bombardment a whole horn, constituted by an r4 mask :. a metal sheet (3> to be etched and an insulating support (2). characterized in that it consists in using as mask <4) a fixed metal mask usable only once. disposing on said mask (4) a positive photosensitive layer (5) which is covered by a removable mask 'bearing the drawing db component to be engraved on said metal sheet. said destiny of the component being transferred in the form of an image to said positive photosensitive layer by the action of a light source, then to chemically etching said image on said fixed mask.  2. Method according to claim 1, characterized in that prior to chemical etching, removing the parts of the positive photosensitive layer which are burnt by the action of the light source are removed.  3. Method according to claim 4, characterized in that the photosensitive resin layer (5) is subjected after deposition to annealing at 90 C for about thirty minutes.  4. Method according to claim 1, characterized in that the fixed mask (4) is deposited by vacuum evaporation on the metal sheet (3).  5. Method according to claim 4, characterized in that the fixed mask is made of chrome.  6. Method according to one of the preceding claims, characterized in that the erosion speed of the fixed mask (4) is less than or equal to that of the metal sheet (3).  7. Method according to one of the preceding claims, characterized in that the thickness of the fixed mask is at least equal to that of the metal sheet.