WO2011124617A1

WO2011124617A1 - Method and device for manufacturing a cylinder of micrometric diameter

Info

Publication number: WO2011124617A1
Application number: PCT/EP2011/055370
Authority: WO
Inventors: Michel Cabrera; Guillaume Girardin; Pierre Morin; Yasmina Layouni; Vincent Semet
Original assignee: Universite Claude Bernard; Ecole Centrale De Lyon; Centre National De La Recherche Scientifique; Institut National Des Sciences Appliquees De Lyon
Priority date: 2010-04-06
Filing date: 2011-04-06
Publication date: 2011-10-13
Also published as: FR2958457B1; EP2555897A1; FR2958457A1

Abstract

The invention relates to a method for manufacturing a cylinder of micrometric diameter in a bar by means of electrolysis, wherein, during the manufacture of a single micrometric cylinder: the voltage V1 alternates (52) between a positive value for a time t+ and a negative value for a time T, which is greater than 1 ms, and the voltage V1 comprises a plurality of time sequences ton in which same alternates between the positive value and the negative value interrupted by sequences in which the voltage V1 is zero for a time t off, which is greater than or equal to 0.1 s.

Description

METHOD AND DEVICE FOR MANUFACTURING A DIAMETER CYLINDER

MICROMETRIC

[001] The invention relates to a method and a device for manufacturing a cylinder of micrometric diameter by electrolysis of a cylindrical bar.

[002] A cylinder is defined by the fact that it has a shape factor greater than 20. The form factor is defined as the ratio between the length L of the cylinder and the mean diameter Dm of the cross sections of the cylinder along the length L, the difference in absolute value between the diameter Dm and the diameter of the cross sections of the cylinder on the length L being less than 30% of the average diameter Dm. A cylinder does not necessarily have a circular section. In the case where the section is not circular, the diameter designates the largest transverse width.

By "cylindricity" is meant a magnitude representative of the maximum deviation in absolute value between the average diameter Dm and the smallest or largest diameter of a cross section over the length L. For example, here, the cylindricity is expressed as a percentage of the average diameter Dm.

[004] By cylinder of micrometric diameter is meant any cylinder whose average diameter of the cross sections along the length L is less than Ι ΟΟμιτι and, preferably, less than 20 μιτι.

[005] The electric current flowing in the electrolyte during electrolysis is called "electrolysis current".

[006] The use of micrometer cylinders is particularly widespread in biotechnology in the production of small-sized electrodes and in microtechnology for microelectro-erosion machining, for example, and in particular in the so-called micro-electro-erosion milling variant (in English "milling micro"). elctrical discharge machining "or" millong EDM "). Currently, these microelectrodes are often manufactured:

(1) by micro-machining by chip removal,

(2) by reverse microelectro-erosion by passing a bar through a calibrated hole so as to thin the bar by electroerosion during the passage, or

(3) by machining a rod by wire microelectroerosion, or

(4) according to a micro-electroerosion variant known in English under the name of WEDG (Wire Electrical Discharge Grinding).

[007] All these methods are based on the use of expensive and bulky machines. Moreover, when the cylinders manufactured are very thin, there is a risk of rupture or mechanical deformation of the cylinder.

[008] Moreover, there are also electrochemical manufacturing processes. With these methods, the machining of micrometric diameter cylinders known include the application of a voltage V1 between the bar and a counter-electrode when the bar and the counter electrode are immersed in an electrolyte.

[009] It is known that the application of a positive voltage V1 between the bar and the counterelectrode causes electrolysis of the bar. Chemical species produced during electrolysis form a viscous layer that flows by gravity along the bar. These species agglutinate around the bar to form a viscous pear-shaped layer. This viscous layer has the effect of slowing down the electrolysis of the area of the coated bar. Conversely, the electrolysis of the uncoated bar zone continues until the bar is broken. This phenomenon is called in English "drop off" effect. Such a method is suitable for the manufacture of tips used inter alia in atomic force microscopes. On the other hand, it absolutely does not allow the manufacture of cylinders of micrometric diameter as described above.

To obtain a cylinder of micrometric diameter using an electrochemical process to avoid the "drop off" effect, it was suggested that there was a specific value of the electrolysis current for which one gets a cylinder and not a tip. This is described in more detail in the following article:

"An electrochemical manufacturing method for extremely thin cylindrical micropin", Young-Mo Lim, Kim Soo Hyun, International Journal of Machine Tools &

Manufacture, 411 (2001) P2287-2296.

However, the specific intensity mentioned in this article is difficult to determine. But for any intensity other than that, a cylinder is not obtained.

The invention aims to provide a simpler method of manufacturing a micrometer cylinder.

It therefore relates to a method of manufacturing a micrometer diameter cylinder in which during the manufacture of the same diameter micrometer cylinder:

the voltage V1 alternates between a positive value for a duration t ⁺ and a negative value for a duration t ^" greater than 1 ms, and

the voltage V1 comprises several sequences of duration t _on which it alternates between the positive value and the negative value interspersed with sequences where the voltage V1 is zero for a duration s greater than or equal to 0.1 s.

When the voltage V1 is negative, the potential difference applied between the bar and the counterelectrode causes the electrolysis of the water causing the production of oxygen and gaseous dihydrogen. Bubbles of these gases accumulate along the bar. If the duration t ^" is greater than or equal to 1 ms, the amount of gas released during the electrolysis of the water is sufficient to stir the electrolyte and prevent clumping of the viscous layer on the bar. with a duration W greater than or equal to 0.1 s allows the gas bubbles released during the electrolysis of water, to rise to the surface of the electrolyte to be evacuated. Thus, the "drop off" effect is removed. The engraving of the bar is homogeneous over a large length of the bar which allows the manufacture of a micrometer cylinder.

Embodiments of this method may include one or more of the following features:

"Does the duration _is less than 100ms and at least greater than the sum of the times t and t +,

^■ the duration t ⁺ is less than 50ms,

^■ the duration is greater than or equal to 1 s,

^■ the duration t is greater than or equal to 10ms,

During the period t ⁺ the method comprises the limitation by an electronic limiter of the intensity of the current flowing through the electrolyte between the bar and the counter-electrode at a value systematically lower than a value L, the value l _m being the value the intensity of the current that would be reached under the same conditions and at the same time if the intensity was limited only by the resistance of the bar, the electrolyte and the counter-electrode

^■ the method comprises:

supplying at least one second bar, in addition to the first bar, capable of being etched by electrolysis, bathed in the same electrolyte, and

the application of a voltage V2 between the second bar and the counter-electrode, the voltage V2 being zero during the duration t _on the first bar and alternating between positive and negative values during the period t ₀ ff of the first bar;

Embodiments of this method further have the following advantages:

^■ the duration t _is less than 100 ms and / or the duration t ⁺ less than 50 ms and / or longer than 1 s and / or the duration t ^"greater than 1 ms possible to obtain cylinders form factor higher and improve their cylindricity;

The use of a current limiter makes it possible to simply control the intensity of the electrolysis current and thus to simply control the quantity of material removed on the bar by electrolysis;

^■ the use of the time t ₀ ff for etching at least a second bar can be manufactured simultaneously several micrometric cylinders, which is a significant time saving.

The invention also relates to a device for manufacturing a cylinder of micrometric diameter in a bar by electrolysis, the cylinder having a form factor greater than 20, the form factor being defined as the ratio between the length L of the cylinder and the mean diameter Dm of the cross-sections of the cylinder along the length L, the difference between the diameter Dm and the diameter of the sections transverse lengths of the cylinder L being less than 30% of Dm, this device comprising:

an electrolyte,

a container containing the electrolyte,

a bar capable of being etched by electrolysis, immersed in the electrolyte,

a counterelectrode immersed in the electrolyte, and

a voltage source capable of applying a voltage V1 between the bar and the counter electrode, the voltage V1 alternating between a positive value for a duration t ⁺ and a negative value for a duration t ^" ,

characterized in that during manufacture of the same cylinder of micrometer diameter, the source is adapted to automatically control the voltage V1 so that:

the duration t ^" is greater than or equal to 1 ms, and

the voltage V1 comprises several sequences of duration t _on which it alternates between the positive value and the negative value interspersed with sequences in which the voltage V1 is zero for a duration t _off greater than or equal to 0.1 s.

Embodiments of this device may include one or more of the following features:

^■ the device contains an electrically insulating fluid within the container, this fluid being immiscible with the electrolyte, heavier than the electrolyte and disposed so that one end of the quenching bar in said fluid, and

^■ the rod includes a proximal end located outside of the electrolyte and a distal end immersed in the electrolyte or in an electrically insulating fluid, each of these ends being mechanically connected by different electrical conductors to the same terminal of the source of voltage.

The embodiments of this device also have the following advantages:

^■ the electrically insulating fluid heavier than the electrolyte possible to prevent shortening of the bar by electrolysis and obtain only radial etching which facilitates control of the shape factor of the cylinder;

^■ Connecting the two ends of the bar to the same terminal of the source with two different conductors makes it possible to obtain a more homogeneous electric potential along the entire length of the bar, which improves cylinder cylindricity.

The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and with reference to the drawings in which:

FIG. 1 is a schematic illustration of a device for manufacturing a cylinder of micrometric diameter, FIG. 2 is a schematic illustration of a waveform of a voltage delivered by a voltage source of the device of FIG. 1.

FIG. 3 is a flow chart of a method for manufacturing a cylinder of micrometric diameter using the device of FIG. 1,

FIGS. 4, 5, 6 and 7 illustrate steps of the method of FIG. 3, and

FIG. 8 is a schematic illustration of a variant of the device of FIG. 1.

In these figures, the same references are used to designate the same elements.

In the following description, the features and functions well known to those skilled in the art are not described in detail.

FIG. 1 illustrates a device 2 for etching by electrolysis. This device 2 comprises a container 4 adapted to contain a liquid substance 6. For example, the container 4 is a polytetrafluoroethylene tank. Here, the capacity of the container 4 is 50ml.

In the embodiment shown, the substance 6 is formed of two immiscible phases superimposed on one another.

The first phase is an electrolyte 8. The electrolyte 8 is an electrically conductive aqueous liquid capable of allowing the electrolysis of a bar 16 immersed in this electrolyte 8. For example, for the etching of a bar 16 tungsten, it is water comprising NaOH and glycerol in solution. Here, the concentration of NaOH is between 1 and 5 mol / liter and the glycerol represents from 0 to 75%, preferably 50%, of the total mass of the electrolyte 8. Preferably, the volume of the electrolyte 8 is between 5ml and 20ml.

The second phase is an electrically insulating oil 14. The function of the oil 14 is to prevent the electrolysis of any element immersed in it. The oil 14 is heavier than the electrolyte 8. For example, the oil 14 is a perfluorinated oil.

The cylindrical bar 16 capable of being etched by electrolysis bathes in the substance 6. Preferably, the bar 16 has a cross section identical to that which it is desired to give the micrometer cylinder. For example, the cross section of the bar 16 is here circular. Preferably, the diameter of the cross section is constant over the entire length of the bar 16 with an initial cylindricity better than the final cylindricity of the cylinder manufactured. The diameter of the bar 16 is strictly greater than Ι ΟΟμιτι. Here, the diameter of the bar 16 is 250μηη. For example, the bar 16 is a 99.9% pure polycrystalline tungsten wire. Advantageously, the initial cylindricity of the bar is at least 5 to 10 times less than the final cylindricity. For example, in the case of the 99.9% pure polycrystalline tungsten bar with an initial diameter of 250 μιτι, it has an initial cylindricity of 3% if it is intended to manufacture a cylinder of micrometric diameter with a cylindricity of 30. %. Preferably, the length of the bar 16 is greater than the height of the mixture 6 in the container 4. The bar 16 has a proximal end 18 and a distal end 20. It is disposed in the container 4 so that the end 18 is located above the electrolyte 8 and in contact with the ambient air. For this purpose, a mandrel 22 suspends the bar 16 by the end 18 in the container 4. The portion of the bar not immersed in the substance 6 corresponds to what is hereinafter called "upper dumbbell".

The bar 16 sinks, for example on at least 6 mm, in the substance 6 so that a portion of the bar is immersed in the electrolyte 8 and another portion is immersed in the oil 14 The portion of the bar 16 immersed in the oil 14 corresponds to what is later called the lower dumbbell 15.

The superposition of the electrolyte 8 and the oil 14 prevents etching by electrolysis of the bar 16 in the longitudinal direction. Indeed, in the absence of oil 14, the etching of the bar 16 would be performed isotropically. Therefore, the etching would progress radially but also longitudinally, which would shorten the length of the bar 16. Thus, in the absence of the oil 14, it is more difficult to control the final length of the cylinder and thus control its form factor. By engraving only radially, the control of the form factor is easier. Thus, during etching, the bar maintains a cylindrical symmetry: (i) of unchanged radius with respect to the initial diameter of the bar in the zones corresponding to the lower and upper dumbbells,

(ii) radius gradually thins between the upper and lower alters,

(iiii) with a continuous fitting gradually flaring from the manufactured micrometer diameter cylinder to the lower or upper dumbbell, the shape of this fitting does not affect the use to be made of the cylinder.

A counter electrode 24 also bathes in the substance 6. The counter electrode 24 is electrically conductive. For example, the counterelectrode 24 is made of brass or copper or, preferably, platinum. Advantageously, the counter electrode 24 surrounds the portion of the bar 16 to be etched. Also preferably, the cross section of the counter-electrode is identical to that which one wishes to give to the micrometer cylinder. Finally, still preferably, the counter electrode 24 is centered on the bar 16. Here, the counter-electrode 24 is a cylinder of circular cross section centered on the bar 16. The counter electrode is for example separated from the bar 16 by a distance greater than 1 mm. Here, this distance is 5 mm. Its structure is, for example, mesh. Preferably, the counter-electrode 24 extends over at least the entire height of the electrolyte 8. A fastener 26 mechanically suspends the counter-electrode 24 in the electrolyte 8.

The device 2 also comprises a voltage source 30 advantageously controlled by computer capable of applying a voltage V1 between the bar 16 and the counter-electrode 24 to cause etching by electrolysis of the 16. The waveform of the voltage V1 is described in more detail with reference to FIG. 2. The voltage source 30 is electrically connected to the bar 16 and to the counter-electrode 24. For example, the voltage source 30 comprises two terminals 31 and 33. The terminal 31 of the source 30 is mechanically connected by an electrical conductor 32A to the end 20 of the bar 16. For example, an electrically conductive crucible 35 is immersed in the oil 14 and provides the electrical junction between the end 20 and the conductor 32A. More specifically, this crucible 35 contains an electrically conductive liquid such as a eutectic liquid metal. For example, the eutectic liquid metal is Indium Gallium 75/25. The end 20 of the bar 16 soaks in this conductive liquid.

The terminal 31 is mechanically connected by an electrical conductor 32B to the end 18 of the bar 16. For example, the conductor 32B connects the mandrel 22 to the terminal 31. The mandrel 22 is then made of an electrically conductive metal.

This so-called "double contact" configuration is preferred for the thinning of very fine tips and allows the bar 16 to have a homogeneous electrical potential over its entire length. It makes it possible to make the etching of the bar 16 by electrolysis more homogeneous over its length immersed in the electrolyte 8. Nevertheless for tips of average diameter, for example 10 μιτι, it is possible to be content with a single electrical contact, ie a lower contact, or a higher contact.

The terminal 33 of the source 30 is mechanically connected by an electrical conductor to the counter-electrode 24.

For example, the source 30 is made from an electronic card 32 of the company National Instrument (registered trademark) sold under the reference USB 6229. The source 30 also includes an application for the card 32 developed under Labview ( registered trademark) making it possible to change over time the waveform of the voltage V1. For example, the amplitude of the voltage V1 is adjustable in steps of 20mV.

Furthermore, the source 30 comprises a controllable current limiter 34 able to limit the intensity of the electrolysis current to a predetermined value and controllable independently of the resistances of the electrolyte 8, the bar 16 and the counter-electrode 24 when a voltage V1 is applied.

FIG. 2 describes the waveform of the voltage V1 applied by the source 30 between the bar 16 and the counter-electrode 24. The voltage V1 is defined by sequences of duration t _on which it alternates between a value positive for a period t ⁺ , and a negative value for a duration t ^" interspersed with sequences of duration W during which the voltage V1 is zero The times t ⁺ , t ^" , t _on and are adjustable in steps of 1 ms. Here, to simplify the control of the amount of current flowing through the electrolyte 8 between the bar 16 and the counterelectrode 24, the waveform of the voltage V1 is square.

The operation of the device 2 will now be described with reference to the method of Figure 3 and with the help of Figures 4 to 7. Here, the method is intended to obtain a cylinder diameter less than 20. , 10 or 1 μιτι and form factor greater than 20 and, preferably, greater than 50. The cylindricté of the cylinder is less than 30% and, preferably, less than or equal to 10%.

In a step 50 the voltage source 30 is configured. More precisely, the amplitude of the voltage V1 and the durations t ⁺ , t ^" , t _on and t ₀ ff are adjusted so that the form factor of the machined roll is greater than 20. Preferably, the form is greater than 30, 50, 100 or 500.

The amplitude of the voltage V1 is chosen sufficiently large to allow the electrolysis of the bar 16 when the voltage V1 is positive and the electrolysis of the water when the voltage V1 is negative. For example, the voltage V1 has a peak-to-peak amplitude of 60V which decreases in steps up to a peak-to-peak amplitude of 10V, 5V or 1.5V. Here, it is centered on 0V. The duration t ⁺ defines the time during which the voltage V1 applied between the bar 16 and the counter-electrode 24 is positive. Therefore, during the period t ⁺ etching of the bar 16 by electrolysis occurs. The electrolysis of the bar 16 in the case of the preceding example (etching of a tunstene bar) involves the following reactions:

in the vicinity of the counterelectrode:

6H ₂ 0+ 6 e ^~ → 3H ₂ (gas) + 6 OH ^~

- in the vicinity of the bar 16:

W (solid) + 8 OH ^~ → W0 ₄ ^{2 ~} + 4H ₂ 0+ 6 e ^~

During the period t ^+, the total reaction occurring in the electrolyte 8 is then:

W (solid) + 2 OH ^~ + 2H ₂ O → W0 ² ₄ ^~ + 3H ₂ (gaseous)

These equations show in a simplified manner the phenomena involved in the etching of the bar 16. The dissolution of the tungsten W causes the creation of an oxide layer which dissolves in the electrolyte 8 to form tungstate ions W0 ₄ . The tungstate ions are heavy and form a viscous layer around the bar 16. If nothing is done, this viscous layer flows along the bar 16 by gravity and forms a pear-shaped mass.

For the shape factor of the final cylinder is greater than 20, the duration t ⁺ is set less than 50ms. Preferably, the duration t ⁺ is less than 10ms, 20ms, 30ms or 40ms. Here, the duration t ⁺ is equal to 10ms.

The time t ^" defines the time during which the voltage V1 applied between the bar 16 and the counter-electrode 24 is negative, therefore, during the period t ^" the electrolysis of the water occurs. The electrolysis of water involves the following reactions: in the vicinity of the counterelectrode:

2H ₂ O (liquid) = 0 ₂ (gaseous) + 4H + (aqueous) +4 th

- in the vicinity of the bar 16:

2H ₂ 0 (liquid) = H ₂ (gaseous) + 2H (aqueous)

The electrolysis of the water produces gaseous dihydrogen and hydroxyl ions in the vicinity of the bar 16. The duration t ^" is chosen such that the quantities of gas produced sufficiently stir the electrolyte 8 in the vicinity of the bar 16 to disperse the viscous layer and prevent its deposition on the bar 16. For example, the duration t ^" is adjusted so that the amount of hydroxyl ions produced during the time t ^" is at least equal to the amount of hydroxyl ions consumed for the duration ⁺ t. for this, the time t ^'is greater than or equal to 1 ms, preferably greater than 5ms, 10ms, 15ms or 20ms. Here, the duration t ^" is equal to 10ms.

[0046] The term t _is also adjusted. The duration t _is used to define the amount of average current per train of positive pulses and thus the etching rate. Furthermore, over time t _is, the greater the roundness of the cylinder tends to decrease. Here, to obtain a micrometric cylinder having a shape factor greater than 20, the time t _it is preferably less than 100ms. However, the tone duration remains long enough to allow at least an alternation of the voltage V1 between its positive and negative values during this time. Here, the duration t _on is equal to 100 ms.

The duration t ₀ ff is long enough to allow the gas bubbles formed during the electrolysis of the water back to the surface of the electrolyte 8. It has been found that if the duration t ₀ ff is too much short, the gas bubbles accumulate along the bar 16 and it leads to a "drop off" effect decreasing cylindricity. Therefore, here the duration t ₀ ff is chosen at least greater than 0.1 s and, preferably, greater than 1 s or 2 s. Here, the duration t ₀ ff is equal to 0.3s.

The speeds of the electrolysis of the bar 16 and the water are determined by the intensity of the current flowing between the bar 16 and the counter-electrode 14 during the periods t ⁺ and t ^" . The intensity of the current electrolysis, in particular during the period t ⁺ , determines the quantity of material removed from the bar 16. The at least approximate knowledge of the quantity of material removed is useful to know when the etching by electrolysis should be stopped. of the bar leads to its disintegration in the electrolyte if the current is applied too long.To easily know the amount of material removed, the current limiter 34 is also configured in step 40. For example, the limiter 34 holds for the duration t ⁺ the intensity of the current at a constant value systematically lower than a value Im, the value Im is the value of the intensity of the current which would be reached in the same conditions and at the same time if the intensity was limited only by the resistances of the bar 16, the electrolyte 8 and the counterelectrode 24. In a step 52, illustrated in Figure 4, the bar 16 is immersed in the substance 6. The source 30 is turned on and the regulated voltage V1 is applied between the bar 16 and the counter-electrode 24 Only the portion of the bar 16 immersed in the electrolyte 8 is etched by electrolysis which digs the periphery of the bar 16 to obtain the desired micrometer diameter cylinder. At the same time, the lower dumbbell 15 is not engraved because it is immersed in the electrically insulating oil 14. Preferably, the amplitude of the voltage V1 decreases in steps. Here, the voltage V1 goes through different stages: 30V, 15V, 10V, 5V and if necessary 1, 5V. Each level lasts respectively 500s, 300s, 200s 100s and 10s. During the first stage, the bar 16 is roughly roughened and the etching is progressively refined by decreasing the amplitude.

To burn quickly, it is advantageous to have a high voltage. On the other hand, if this tension is applied too long, the cylindricity of the cylinder situated between the two dumbbells is deteriorated. To avoid this, it is advantageous to adapt the etching rate to the diameter of this cylinder, that is to say, to slow the etching rate when the cylinder becomes thin to avoid its disintegration. This adaptation is performed by lowering the tension as thinning. Advantageously, the voltage drop is applied in stages as a function of time. It is also possible to increase the number of steps to have a continuous decrease of the applied voltage. Be that as it may, the duration of the last stage is shortened or prolonged until the cylinder engraved between the two dumbbells has the desired diameter. In this case, the source 30 is turned off. For example, at regular time intervals (multiple of the sequence t _on ) a laser micrometer, marketed by Mitituyo (trademark) under the reference LSM-500s capable of measuring diameters of between 5 μιτι and 1 mm, measures the diameter of the cross section of the bar 16. Advantageously, the micrometer measures the general shape of the bar and thus the form factor and cylindricity of the cylinder. Here, the resolution of the laser micrometer used is 10 nm. An actuator is able to stop the source 30 when the desired diameter is reached. At this stage, the desired micrometer cylinder (FIG. 5) has been obtained, but it is still attached to the dumbbell 15.

To separate the dumbbell 15 from the micrometer diameter cylinder, during a step 54 illustrated in Figure 6, the bar 16 is partially removed from the mixture 6 so that the upper part of the dumbbell 15 attached to the cylinder of micrometer diameter is immersed in the electrolyte 8. For example, the bar 16 is arranged such that the dumbbell 15 fully immersed in the electrolyte 8. The zone of the bar 16 etched in step 52 is at more than 80% or 90% in ambient air.

Then, during a step 56 shown in Figure 7, the dumbbell 15 is separated from the micrometer cylinder. For example, this is done by electrolysis. For this purpose, the source 30 applies a voltage V1 continues to cut the end of the micrometer cylinder in contact with the dumbbell 15, for example, by "drop off" effect.

Finally, during a step 58 the micrometer cylinder is removed from the mixture 6.

If necessary, the distal portion of the bar can be flattened by mechanical means or electroerosion, for example, against a less easily erodable material that the bar and / or EDM conditions known to man of the art (polarity of applied voltage, level and form of applied voltage).

The device and the method described above makes it possible not only to manufacture cylinders of micrometric diameter but also cylinders of submicron diameter (that is to say less than 1 μιτι) with a high form factor and a cylindricity better than 30%. For example a cylinder of 0.1 μιτι in diameter can be manufactured. Moreover, the manufacturing process is fast. Indeed, its duration is between 5 and 120 minutes and most often between 5 and 20 minutes. It can be completely automated. The method does not use any expensive components (except for the omitted laser micrometer). As an illustration of the above, a version of the engraving machine has been developed (without laser micrometer) with a fully microcontrolled control for less than 300 euros of electronic components and less than 2000 euros of motors and components mechanical.

8 illustrates a device 60 identical to the device 2 except that it is able to simultaneously manufacture at least two micrometer diameter cylinders. For this purpose, the device 60 comprises an additional bar 62. This bar 62 is able to be etched by electrolysis. It bathes in the same mixture 6. The bar 62 has a proximal end 64 and a distal end 66. For example, it is disposed in the container 4 so that the end 64 is located above the electrolyte 8 in the ambient air. For this purpose, a mandrel 68 suspends the bar 62 by the end 64 in the container 4. For example, the bar 62 is identical to the bar 16. The end 66 bathes in the same conductive bath contained in the crucible 35.

The source 30 is replaced by a source 69 adapted to apply the voltage V1 between the bar 16 and the counter-electrode 24 and a voltage V2 between the second bar 62 and the counter-electrode 24. The voltage V2 is temporally synchronized on the voltage V1 so that the current flows only alternately between the bar 16 and the counter-electrode 24 and between the bar 62 and the counter-electrode 24. This allows to better control the amount of material removed on each of the bars while simultaneously engraving these bars. Here, the voltages V1 and V2 are identical except that the duration t _on one corresponds to the duration t ₀ ff of the other. The operation of the device 60 is identical to the device 2 except that the voltage V2 is zero for the duration t _on the voltage V1 and the voltage V2 alternates between the positive values and the negative values during the duration of the voltage V1. This embodiment makes it possible, when one of the bars is not etched during the duration W to engrave the other. As a result, the production speed of two cylinders is improved.

Of course, it is possible to use different voltages to lead directly to different diameters, shape factors and / or degrees of cylindricity. In particular, achieving tips of different diameters may be advantageous depending on the applications. For example, if the tips are used for microelectro-erosion milling, it is advantageous to simultaneously make tips that will be used for a rough roughing phase with a large diameter tip and a finishing phase with a smaller diameter tip. . Possibly holes may be made with tips of different diameters but perfectly calibrated.

Many other embodiments are possible.

The insulating oil 14 may be omitted. In this case, the electrolysis of the bar 16 is carried out over the entire immersed length of the bar.

A peristaltic pump may be added to the device 2 for the purpose of renewing the electrolyte continuously. It is also possible to continuously filter the electrolyte by nanofiltration and / or electrodialysis in order to extract the tungstate ions formed during the electrolysis of the bar and / or to reconstitute the hydroxyl ion concentration of the electrolyte 8.

The chemical composition of the electrolyte 8 is not limited to the composition given by way of example. Similarly, the concentrations of NaOH and glycerol of the electrolyte 8 are not limited to the case described. Moreover, the viscosity of the electrolyte 8 can be adjusted by another chemical species than glycerol. Glycerol or any other compound for adjusting the viscosity of the electrolyte 8 may be omitted from the electrolyte 8.

The invention is not limited to the case where the waveforms of the voltages V1 and V2 are square. It is perfectly conceivable that the voltages V1 and V2 are sinusoidal or sawtooth or with other waveforms as long as it has durations t ^" , t ⁺ , t _on and as described above.

In another embodiment, the voltage V2 of the device 60 of Figure 3 is such that one of the bars is machined to produce a cylinder while the second is machined to achieve a peak. For example, the voltage V2 has no negative half cycle for the time t _on to burn the second bar by effect "drop off". It is then possible, for example, to use the second bar as a probe for a tunneling microscope. More specifically, it would be conceivable to arrange these two bars in a single machine for machining a workpiece by microelectro-erosion milling with the first bar and to characterize the surface of said workpiece tunneling effect with the second bar. It appears from what precedes that the ability to simultaneously manufacture multiple tips with the present invention and with a perfectly controlled shape and arrangement in space, is a significant advance over the state of the art.

The voltage source 30 may possibly not include a current limiter 34, the current being then limited only by the electrical resistances of the bar 16, against the electrode 24 and the electrolyte 8. The invention is not limited to the case where the limiter 34 maintains the intensity of the current at a constant positive value during the period t ⁺ and at a constant negative value for the duration t ^" It is possible to envisage a control of the current only during the duration t ⁺ or only during the period t ^" . Similarly, it is possible to envisage a current control by the limiter 34 so that during the periods t ⁺ and t ^" the current decreases according to a predetermined and imposed slope.

The etching by electrolysis can be stopped depending on an estimate of the amount of material removed. This estimate is for example obtained from the measurements of an ammeter connected to the supply conductors of the source 30. Under these conditions, the laser micrometer measuring the diameter of the cylinder can be omitted.

The bar 16 and the cylinder manufactured are not necessarily cylinders with circular cross section. It can be a cylinder with rectangular section, elliptical or any type of section.

Any material capable of being etched by electrolysis can be used in the context of this invention as a bar. For example, one can use a monocrystalline or polycrystalline tungsten rod, platinum-iridium Pt-1r, tungsten carbide, platinum, graphite, molybdenum, nickel, gold, titanium or silver.

In the case where the bar is made of tungsten carbide or one of its alloys, it is possible to use an electrolyte comprising NaOH with a concentration of 2mol / liter or H ₂ SO ₄ with a concentration of between 0.5mol / liter and 2 , 5mol / liter or NaCl.

In the case where the bar is platinum or platinum-iridum Pt-1r can be used an electrolyte comprising NaCl or CaCl ₂ .

In the case where the bar is graphite, can be used an electrolyte comprising a NaOH solution with a concentration of between 4mol / liter and 8mol / liter.

In a variant, the counter-electrode is made of Pt platinum or nickel Ni.

What has been described above is not limited to the case where the counterelectrode is cylindrical. The counter-electrode may also be a simple bar bathed in the electrolyte next to the bar to be etched.

The measurement of the diameter of the bar 16 etched is not necessarily achieved using a laser micrometer. To measure tips with a diameter of less than 5 μιτι, it is possible to use high precision optical methods: a goal of microscope of very high resolution (0.4 μιτι for example) and of great working distance (6 mm for example) or an interferometer or a device based on a principle derived from that exposed in the following publication:

Ezio Puppin, "Displacement measurements with resolution in the 15 pm range",

REVIEW OF SCIENTIFIC INSTRUMENTS 76, 105107 (2005)

The manufacturing process is not limited to the etching of two bars in parallel. It is possible to use the manufacturing method described with reference to FIG. 3 or 8 to simultaneously engrave a number of bars greater than or equal to three. For example, if the method described with respect to FIG 8 is made to burn more than three bars, durations t _on burning these bars are distributed to not overlap.

Finally, it is also possible to accelerate the etching by increasing the current flowing through the bar and / or by varying the electrolyte concentration.

Claims

1. A method of manufacturing a cylinder of micrometer diameter in a bar by electrolysis, the cylinder having a form factor greater than 20, the form factor being defined as the ratio between the length L of the cylinder and the mean diameter Dm of the cross sections of this cylinder on the length L, the difference in absolute value between the mean diameter Dm and the diameter of the transverse sections of the cylinder on the length L being less than 30% of the average diameter Dm, this method comprising the application (52) a voltage V1 between the bar (16) and a counter-electrode (24) when the bar (16) and the counter-electrode (24) are immersed in an electrolyte (8),

characterized in that during manufacture of the same micrometer diameter cylinder:

the voltage V1 comprises several sequences of duration t _on which it alternates between the positive value and the negative value interspersed with sequences in which the voltage V1 is zero for a duration greater than or equal to 0.1 s.

2. The method of claim 1 wherein t _is the duration is less than 100ms and at least greater than the sum of the times t and t ⁺ ^".

3. Method according to any one of the preceding claims, wherein the duration t ⁺ is less than 50 ms.

4. Method according to any one of the preceding claims, wherein the duration t _off is greater than or equal to 1 s.

5. Method according to any one of the preceding claims, wherein the duration t is greater than or equal to 10 ms.

6. Method according to any one of the preceding claims, wherein, during the period t ⁺ , the method comprises the limitation by an electronic limiter (34) of the intensity of the current flowing through the electrolyte between the bar and the counter- electrode at a value systematically lower than a value l _m , the value l _m being the value of the intensity of the current that would be reached under the same conditions and at the same time if the intensity was limited only by the resistances of the bar (16 ), the electrolyte (8) and the counterelectrode (24).

The method of any one of the preceding claims wherein the process comprises:

- Providing at least one second bar (62), in addition to the first bar (16), capable of being etched by electrolysis, bathed in the same electrolyte (8), and

the application of a voltage V2 between the second bar (62) and the counter-electrode (24), the voltage V2 being zero during the duration t _on the first bar and alternating between positive and negative values during the period t ₀ ff of the first bar.

8. Device for manufacturing a cylinder of micrometric diameter in a bar by electrolysis, the cylinder having a form factor greater than 20, the form factor being defined as the ratio between the length L of the cylinder and the average diameter Dm of transverse sections of the cylinder along the length L, the difference between the diameter Dm and the diameter of the cross-sections of the cylinder on the length L being less than 30% of Dm, this device comprising:

an electrolyte (8),

a container (4) containing the electrolyte,

a bar (16) capable of being etched by electrolysis, immersed in the electrolyte (8),

a counterelectrode (24) immersed in the electrolyte (8), and

a source (30) of voltage able to apply a voltage V1 between the bar (16) and the counter-electrode (24),

characterized in that during manufacture of the same micrometer diameter cylinder, the source is programmed to automatically control the voltage V1 so that:

the voltage V1 comprises several sequences of duration t _on which it alternates between the positive value and the negative value interspersed with sequences where the voltage V1 is zero for a duration greater than or equal to 0.1 s.

9. Device according to claim 8, wherein the device contains a fluid (14) electrically insulating contained in the container, the fluid being immiscible with the electrolyte, heavier than the electrolyte and arranged so that a end (20) of the bar dipped in this fluid.

10. Device according to any one of claims 8 to 9, wherein the bar (16) comprises a proximal end (18) located on one side, outside the electrolyte and a distal end (20) immersed in the electrolyte (8) or located on the other side of the electrolyte, each of these ends being mechanically connected by different electrical conductors to a same terminal (31) of the voltage source (30).