WO1986000094A1

WO1986000094A1 - Etching

Info

Publication number: WO1986000094A1
Application number: PCT/EP1984/000232
Authority: WO
Inventors: Slavik Zdenek
Original assignee: Hans Höllmüller Maschinenbau GmbH & Co.
Priority date: 1984-06-16
Filing date: 1984-06-16
Publication date: 1986-01-03
Also published as: EP0200719A1; JPS61502471A

Abstract

A method of etching material by subjecting the material to chemical action by a liquid etchant and a device for performing said method. An electrolyser (26) is provided for recovery of etched material from the etchant by electro-deposition. The electrolyser (26) is a substantially closed or closable vessel with cathode and anode electrodes positioned therewithin. Pump means (P1) is provided for effecting flow of the etchant from an inlet to an outlet of the vessel whereby on application of an electric potential to the electrodes the etched material is deposited on one of the electrodes. The method is especially useful in the recovery of copper from CuCl2-etchant by direct electro-deposition without accompanying development of chlorine gas.

Description

"ETCHING"

This invention relates to methods and apparatus for etching and particularly, but not exclusively, to such methods and apparatus applicable to the etching of copper, for example in the formation of electric circuit boards.

A known form of etching process for electric circuit boards utilizes a liquid etchant of the alkaline copper chloride type. A typical etchant may be made Up as follows:

Constituent Molarity g/l CuCl₂ (anhydrous) 0.5 67 (32 g/l Cu)

NH₄Cl 3.0 160 MH₃ (as MH₄OH or (NH₄)₂CO₃) 5.0 35 (320m/l of 30% ammonia s.g.O.895) A full explanation of the electro-chemical processes involved is giver, in the Research Laboratory Report No. 7333 published in 1980 by the Australian Telecommunications Commission and entitled "ELECTRIC REGENERATION OF ETCHING SOLUTION FOR PRINTED WIRING". For the present purposes it is sufficient to note that the etching process, as effected on copper material using this etchant, is principally governed by the following reaction:

CuCl₂ + Cu = Cu₂Cl₂ or, in ionic form

Cu⁺⁺ + Cu^o = 2 Cu⁺

Thus the cupric chloride is the oxidising agent employed. By the above reaction alone, most of the available cupric ions would soon be reduced into the inactive cuprous form after which etching would stop. However, the composition is such that the cuprous chloride is present in an ammonia complex which is easily oxidisable back to cupric salt by atmospheric oxygen and, in practising the process, steps are taken to ensure access to atmospheric oxygen such as to regenerate cupric chloride in the required form. This is effected in accordance with the following reaction: Cu₂Cl₂ + 2 NH₄Cl + H₂O + ½O₂ = 2 CuCl₂ + 2 NH₄OH or

2 Cu⁺ + 2 NH₄ + + H₂O + ½O₂ = 2 Cu^{+ +} + 2 NH₄OH

In practising the above described method, certain factors are important in maintaining efficient operation. Firstly, it is necessary to maintain the pH of the etchant within predetermined limits. For optimum operation, the pH at 50°C should, for example, be between 9.4 and 9.6. However, ammonia tends to be lost in practice through evaporation or through direct loss by "dragσut" on articles when they are removed from the etchant. Secondly, notwithstanding the regenerative process described above, the etchant will eventually reach a buildup of removed copper such that further etching will be inhibited. Also where the copper content is low, the etch rate will also be correspondingly low. Although in practice etchant will perform satisfactorily over a wide range of copper contents, and although the etchant is capable of considerable removed copper retention, it is therefore necessary to either discard the etchant after a certain amount of use has occurred or to somehow regenerate it by removing excess copper.

The aforedescribed Research Laboratory Report No. 7333 describes an etchant regeneration system which uses electrolytic regeneration to remove the excess copper by direct deposition on the cathode of an electrolytic cell, or electrolyser.

One difficulty with the known etchant regeneration process is that, in practice, it has been found difficult to achieve a satisfactory flow rates through the electrolyser, so that the current density applied has correspondingly been limited, by virtue of the occurrence of concentration polarisation, to values less than desirable for best results. In this regard, the electrolvsers have been formed as open vessels. In one aspect, then, the invention provides, an electrolyser for use in recovery of etched material from a liquid etchant, comprising a substantially closed or closable vessel with cathode and anode electrodes positioned therewithin, said vessel being provided with inlet and outlet means for flow of said etchant through the vessel, said electrodes being positioned whereby in use to effect deposition of said etched material on one of said electrodes when said etchant is passed through the vessel and electric potential is applied across said electrodes.

The invention further provides etching apparatus of the kind in which material to be etched is subjected to chemical action by liquid etchant wherein an electrolyser is provided for recovery of etched said material from the etchant by electro-deposition of the etched material, said electrolyser being the form of a substantially closed or closable vessel with cathode and anode electrodes positioned therewithin, said vessel being provided with an inlet arid an outlet, pump means being provided for effecting flow of said etchant through the vessel from said inlet to said ouriet whereby on application of an electric potential to said electrodes, when said etchant is passed through the vessel, said etched material is deposited on one of said electrodes. The pump means may be arranged to effect said flow from an etchant retention chamber which recovers etchant after contact with said material to effect etching. This invention also provides etching apparatus of the kind in which material to be etched is subjected to chemical action by a liquid etchant, wherein means is provided for detecting the quantity of said material in the etchant and operable to electrolytically deposit out of the etchant at least a portion of the material in the etchant on detection of an excess of said material in the etchant.

In a still further aspect, the invention provides etchant apparatus of the kind in which material to be etched is subject to chemical action by a liquid etchant, having means for detecting the quantity of said material in the etchant, said means comprising means operable to pass the etchant through a narrow passageway, means for directing light through etchant flowing through said passageway, and means for detecting the amount of light so passing through the etchant whereby to provide an indication of said quantity in accordance with the light absorbance of the etchant. The detecting means may be connected to operate the electrolyser described above, under circumstances where the light absorbance is detected as being indicative of increase of the quantity of said material in the etchant above a predetermined level, whereby to reduce the quantity to a level below said predetermined level. Said passageway is preferably narrow in the direction of passage of said light but wide in the direction normal thereto.

In a still further aspect, the invention provides etching apparatus of the kind in which material to be etched is subjected to chemical action by a liquid etchant, wherein means is provided for monitoring the content of at least one component of the etchant and effective to add to said etchant a quantity of said component when the concentration thereof falls below a predetermined level. For example the pH of the etchant may be directly measured. The invention also provides, in an alternative construction, etching apparatus of the kind in which material to be etched is subjected to chemical action by a liquid etchant wherein means is provided for adding to said etchant a component thereof which in use of the apparatus tends to be depleted, the apparatus being arranged whereby in use during adding of said component, such as between separate individual dosings or during a continuous dosing, a property of said etchant is monitored and determinations are made as to whether that property has been altered as compared to a preceding determination. In this arrangement, the dosing may be ceased after said property is found no longer to be altering, such as where two consecutive said determinations are similar. The physical property is preferably the light absorbance of the etchant In the case where the etchant is the described alkaline cuprous chloride, said component may comprise ammonia or an ammoniacal composition, the light absorbance of the etchant at a particular wavelength or band of wavelengths being the property of the etchant which is determined. Addition of said component may be initiated automatically at, say, predetermined times. In a still further aspect of the invention there is provided an electrolyser for recovery of etched material retained in a liquid etchant, said electrolyser comprising a vessel having cathode and anode electrodes therein, a barrier dividing the interior of said vessel into two portions, one containing the cathode electrode and the other containing the anode electrode, such that liquid communication between the interior portions otherwise than through the barrier is in use precluded, said vessel being arranged for reception of said etchant in said one interior portion and for reception in said other interior portion of an anolyte liquid, said barrier being porous whereby to permit said, anolyte liquid to pass therethrough but such as to preclude said material or at least some form thereof from passing therethrough; said etchant and said anolyte liquid in use providing an electrically continuous medium between said electrodes such that, on application of electric potential across said electrodes, said material is deposited by electrolytic action on said cathode. The electrolyser may be closed or closable as above described. The etchant containing said material may be circulated through said one interior portion and said anolyte liquid may be circulated through said other interior portion. Where said material comprises copper said barrier is designed to be impervious at least to Cu⁺ ions.

In another aspect, the invention provides a method of recovery of etched material from a liquid etchant comprising passing the liquid etchant through a substantially closed vessel so as to contact cathode and anode electrodes positioned within the vessel, and applying an electric potential across said electrodes whereby to remove said etched material from said etchant by electrolytic action.

The invention further provides a method of etching material by subjecting the material to chemical action by a liquid etchant characterised by the step of recovering the etched material from the etchant by the last described method.

The invention also provides a method of etching in which material to be etched is subjected to. chemical action by liquid etchant, including the step of detecting the quantity of said material in the etchant and electrolyticaliy removing from the etchant at least a portion of said material in the etchant on detection of an excess of said material in the etchant.

In anocher aspect, the invention provides a method of etching in which material to be etched is subjected to chemical action by a liquid etchant, including the step of detecting the quantity of said material in the etchant, by passing the etchant through a narrow passageway, directing light through the etchant passing through said passageway, and detecting the amount of light so passing through the etchant, thereby providing an indication of said quantity in accordance with the liσht absorbance of the etchant. In a still further aspect, the invention provides a method of etching in which material to be etched is subjected to chemical action by a liquid etchant, including the step of monitoring the content of at least one component of the etchant and adding to said etchant a quantity of said component when the concentration thereof falls below a predetermined level.

In an alternative method in accordance with the invention, there is provided a method of etching in which material to be etched is subjected to chemical action by a liquid etchant, including the steps of adding to said etchant a component thereof which is in use depleted, making a plurality of time spaced measurements of a property of said etchant, and terminating said addition pursuant to said measurements showing said property to be substantially unchanging.

The invention still further provides a method of recovery of etched material retained in a liquid etchant, comprising positioning the etchant containing the material as well as an anolyte liquid in a vessel such that these are divided one from the other by a barrier which is porous whereby to permit said anolyte liquid to pass therethrough but such as to preclude said material, or a form thereof, from passing therethrough, and subjecting the said etchant and said anolyte liquid to an electric potential by means of electrodes, a respective one positioned in each, whereby to effect removal of said material from said etchant by electrolytic action.

The invention is further described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a diagram of an etching apparatus constructed in accordance with the invention;

Figure 2 is a diagrammatic end view of a detector incorporated into the apparatus of figure 1; Figure 3 is a perspective view of the detector of figure 2;

Figure 4 is a perspective view of a flow device incorporated into the detector of figure 3;

Figure 5 is a cross sectional view of an etchant electrolyser constructed in accordance with the invention;

Figure 6 is a plan view of the electrolyser of figure

1, partly broken away;

Figure 7 is a diagram of circuit components forming part of the detector of figure 2; and

Figure 8 is a circuit diagram showing further circuit components of the detector of figure 2.

Figure 1 shows the general schematic arrangement of an etchant apparatus constructed in accordance with the invention. The apparatus includes, as is conventional, an etchant tank 10 in which the liquid etchant or catholyte 12 is retained. In normal operation, a pump PI pumps liquid from che tank 10 through a solenoid valve 14 and thence through two ball valves 16, 18, to nozzles 17 which direct the catholyte on to an article to be etched (not shown) from whence the catholyte returns to the tank. Usually, provision is made for moving the article to be etched through the streams of catholyte emerging from the nozzles. The preferred catholyte for use in the invention is the aforedescribed, alkaline CuCl₂ liquid made up of CuCl₂, NH₄Cl and NH₃ (as NH₄OH or (NH₄)₂CO₃) Copper on the article to be etched is thus etched as previously described so that the resultant catholyte 12 becomes enriched with copper. When rejuvenation of the catholyte is required, the valve

14 is closed and, with pump PI operating and solenoid valve 20 open, the catholyte is taken from tank 10 via a ball valve 22 , valve 20 , a barrier valve 24 and a line 29 through an electrolyser 26 and thence from the electrolyser via a line 28 to be returned to the tank 10.

The construction of the electrolyser 26 will be more apparent from figure 5 and 6. More particularly, the electrolyser comprises a generally cylindrical open topped vessel 30, preferably made of titanium. The top of the vessel is closable by a lid 32 having a sealing ring 34 positioned in a groove on the underside thereof. The lid is sealingiy engagable on the vessel 30 so that the ring 34 provides a peripheral seal against an outstanding rim 36 of the vessel 30. Sealing is effected by screwing down of butterfly nuts 38 on threaded elements 40, which extend upwardly from outstanding lugs 42 positioned around the periphery of the vessel 30 below rim 36. Elements 40 extend upwardly from lugs 42 through openings 44 in the lid 32. The nuts 38 bear against the lid 32 to securely clamp it into engagement with rim 36 . As shown, the openings 44 may be open to the periphery of the lid 32 and the elements pivotally secured, by pivot pins 48, to the lugs 42 whereby to facilitate removal of the lid 32 by first unscrewing nuts 38 sufficiently to release pressure on the lid and thence pivoting the elements 40 outwardly to clear these from the openings 44. Wich lid 32 in the closed position, the interior of the vessel 30 is substantially closed.

An anode structure 50 is contained within the interior of vessel 30. Structure 50 comprises a cylindrical platinumised titanium mesh anode 52, opposite ends of which interfit with respective circular grooves in opposed electrically conductive discs 54, 56. The anode structure 50 is retained within a partitioned space 51 within the interior of essei 30 which is closed and separated from the remainder of the vessel. More particularly, an elongate tubular ceramic sleeve 58 is provided within the interior of the vessel. This is retained between opposed discs 60, 62 to either end thereof and the space 51 is defined within the sleeve 58 and between discs 60, 62. T.he opposite ends of the sleeve 58 are received within circular grooves in the respective discs 60, 62 and circular sealing rings 64, 66 are provided in the grooves so arranged as to seal the gaps between the ends of the sleeve 58 and the discs 60, 62.

Disc 62 rests on the floor of the vessel 30 and disc 60 is spaced somewhat below rhe upper end of the vessel. A central electrically conductive rod 70 is connected to disc 58 and extends upwardly therefrom and thence through an opening in disc 54. Rod 70 is threaded at a location where the rod passes through disc 54 and a threaded element 72 is threadedly received thereon and tightened against the exterior of disc 54 to clamp anode 50 between the discs 54, 56. At the lower end of the sleeve 58, the disc 62 is secured to the base of vessel 30 by means of a coupling element 30 which extends through the base and into the disc 62. Rod 70 extends upwardly from disc 54 through a central opening in disc 60. An element 84 is threadedly received on a portion of rod 70 where this emerges from disc 60 and is tightened .down to exert pressure against disc 60 whereby to clamp sleeve 58 securely between the discs 60, 62. An insulating bushing 86 is threadedly received in a threaded opening in element 84 and extends upwardly therefrom and through a central opening in lid 32. An electrically conductive anode terminal post 90 is secured to lid 32 and depends downwardly therefrom through bushing 86 to make electrical contact with the end of rod 70 adjacent disc 60. During removal of lid 32, the terminal post 90 can.be withdrawn through bushing 86, or the bushing 86 and terminal post 90 may together be removable from element 84, such as by unscrewing bushing 84.

Terminal post 90 provides for electrical connection to the rod 70 which thence provides electrical connection via the discs 54, 56 to the anode 52. The cathode 100 for the electrolyser is the form of a cylindrical stainless steel shim which is curved around the inner surface of the side wall of the vessel 30 so as to be an intimate electrical contact therewith. Electrical contact thereto is provided by a terminal 35 which is formed on vessel 30.

A lower inlet 102 is provided in the base of the vessel for admission of the catholyte and a side outlet 104 is provided at the upper end of the vessel for exit of catholyte. These are disposed so that the path of catholyte flow is exterior to the space 51 defined between the sleeve 58 and discs 60, 62. The flow is thus upwardly from inlet 102 in a space 53 between the sleeve 58 and side wall of vessel 30 and thence outwardly through outlet 104.

Means is provided for admission of a liquid anolyte, for a purpose described later, through the coupling element 80 from whence it passes upwardly to pass through outlet openings 80a in an upstanding flange portion of disc 56 into the interior of the anode 52, towards the base thereof. An outlet 108 for the anolyte is provided at the base of the vessel 30. This interconnects with a tube 110 which extends upwardly in the space 53 between the sleeve 58 and a side wall of the vessel 30 to a fitting 112 which provides fluid flow interconnection between the interior of the tube 110 and the interior space 51. Fitting 112 is carried on disc 60 and provides for fluid flow through the disc 60 at a location offset from the axis thereof. Reverting again to figure 1, the apparatus therein shown includes a tank 120 for the aforementioned anolyte 115. A pump P2 is provided for pumping anolyte from tank 120 to coupling element 80 for flow upwardly through the space within sleeve 58, through the anode 52 itself thence through fitting 112 and tube 110 to exit via outlet 108. Outlet 108 is connected for return of anolyte through a heat exchanger 124 back to tank 120.

When, as a foredescribed, valves 20, 22, 24 are open, flow can occur by operation of pump PI from tank 12 so that the catholyte therein is passed to inlet 102 for exit from outlet 104 and returned by line 28 to the tank 10.

The aforedescribed anolyte is a liquid which may be is identical in composition to the etching solution of catholyte save that there is no copper containing component.

A suitable anolyte may comprise the following: Ammonium hydroxide soln. 35% - 500ml/L Ammonium Chloride - 4 to 6 M

This solution is generally the same as chat of the catholyte, save for the absence of a copper component, and may be used as the source of replenishment ammonia as is described later.

The sleeve 58 is formed of a ceramic material having pores therein so that fluid flow can occur therethrough. The size of the oores is such as to facilitate operation of the electrolysers as described later. For the moment it is merely noted that the pore size is such as to permit anolyte to pass through the sleeve so that the catholyte and anolyte together form a continuous electolyte path from the cathode 100 to the anode 50.

To effect removal of excess copper from the catholyte, the aforementioned circulation of both anolyte and catholyte through the electrolyser 26 is effected and an electric potential applied across the anode and cathode from a source 130. The result of this is to effect deposition of copper on the cathode 100. By making the cathode of a suitable material, such as the described stainless steel shim, the deposited copper may be removed by subsequently removing the cathode from the electrolyser 26 and flexing it. It has been found that source 130 may, suitably, be effective to provide 15 volts across the anode and cathode with a current capacity of about 300 amps.

The barrier presented by the sleeve 53 serves the following purpose. Firstly, at the cathode 100, cupric ions may either be reduced to cuprous ions by the reaction:

H⁺ + e- = H° and Cu⁺⁺ + H°→ Cu⁺ + H⁺

or alternatively the reaction could proceed to metallic copper by further reduction

Cu⁺ + e- → Cu° at a somewhat more negative potential applied to the cathode than that required for the reduction of hydrogen However, that part of the cupric ions which is merely reduced to cuprous ions represents a total loss of efficiency. Cuprous ions also tend to be subsequently oxidised back to cupric ions by atmospheric oxygen. Alternatively, the reoxidisation may occur even more rapidly if the catholyte were allowed to mix freely with the anolyte, since oxygen is being generated at the anode by the reaction: 2OH- - 2e- = H₂O + ½O₂.

The barrier provided by sleeve 58 serves to prevent mixing of the catholyte and anolyte and reoxidatisation of the cuprous ions in the region of the anode, whilst also changing the electro-chemical gradient across the cell in favour of higher polarisation of the cathode required for the reduction of cuprous, possibly even cupric ions into metallic copper.

In order to ensure largely automatic operation, it is necessary to sense conditions at which operation of the electrolyser 26 should be initiated in order to preserve a proper copper content in the catholyte for effective operation. This operation is effected under control of a copper detector and command unit 132. This is arranged to receive a small subsidiary flow of catholyte via a fluid flow line 31 from the line 29 which provides connection between the tank 10 and electrolyser 26. Line 31 passes through a suitable filter 134 thence through unit 132 and thence back to join line 28 at the outlet of the electrolyser 26.

The purpose of the copper detector alnd command unit 132 is to monitor the copper content in the catholyte. Generally, this is effected by passing the catholyte, from filter 134 and thence through a flow device 136. A light beam is directed through the flow device and catholyte flowing therethrough and the relative intensity of the emergent light is detected whereby to provide a measure of the light absorbance of the catholyte. Shown best in figure 4, flow device 136 comprises a flat body 138 which may be formed of a plastics material which is light transparent. The body 138 presents two opposed parallel planar panels

139, 141, the space between these being closed at four sides so as to define an interior chamber 143 therebetween. Chamber 143 presents a gap "G" between the panels 139, 141 which is of small dimension. Preferably, the gap is less than 0.35mm. At either end of the body 138, there are provided inlet and outlet connections 131a, 131b for interconnection of the flow device into the previously mentioned line 31. A helium-neon laser tube 145, is provided as a light source and this is positioned so that light therefrom passes on a line 145a through a band pass filter 147, a beam splitting mirror 149, and thence through the body 138, passing normally through panels 141, 139 and the catholyte in the body 138 to emerge from panel 139. A light detector 151 is positioned to receive emergent light. The flow device 136 may be received in a cavity within a supporting housing 139 having aligned openings 139a, 139b for passage of light from laser tube 145.

It has been found that the copper content of the catholyte can be monitored by measuring the light absorbance of the catholyte at a wave length of approximately 633 nM (the wavelength of light generated by the laser tube 145). The aforementioned 633 nM wavelength closely corresponds to the peak absorbance frequency for the complex [Cu(NE₃)₄] ⁺⁺. Filter 149 is a 10A red filter and minimises blue and green interferral radiation.

The signal from detector 151 may be processed such as is shown in figure 8 by sampling and holding measured signal output from the detector, such as in the sample and hold circuit 155 shown, passing sample signals to a comparator 156 and comparing tiie sample values with a reference signal to produce an output signal suitable for effecting control of the valves and pumps beforedescribed, particularly the solenoid valves 14 and 20. Since light absorbance increases with increase in content of the complex [Cu (NH₃)₄]^{+ +}, the comparator may serve to generate an output signal which causes valve 14 to be closed and valve 20 to be open so long as sampled signal from detector 151 is less than a desired reference. Thus, the arrangement is such that, periodically pump PI may be operated, with valve 14 closed and valve 20 open, so as to pass catholyte through the copper detector and command unit 132 and the electrolyser 26. Where, pursuant to this, it is determined by comparator 156 that the copper content is above that needed for optimum operation, comparator 156 generates a control signal which is applicable to cause source 130 to apply electric potential between the cathode and anode of the electrolyser 26. This operation would continue until such time as the control signal from the comparator 156 became indicative of fall of the copper level to a desired value, whereupon valve 20 may be closed and valve 14 opened to revert the apparatus to normal use. Arrangements may then be made for draining the electrolyser 26 as desired.

The reference signal applied to comparator 156 may be derived from a reference detector 153 receiving reflected light from the beam splitter 149. Thus, even though the output of the laser tube may vary, thus affecting the light falling on the transmission detector 151 independently of the copper concentration of the catholyte flowing through the detector unit 132, the desired reference level from detector 153 as applied to the comparator 156 will be varied in a manner to compensate for that light variation.

The light absorbance of the aforementioned complex [Cu(NH₃)₄]⁺⁺ is very high and it is for this reason that the flow device 138 is arranged so that the chamber 143 therein is narrow in the direction perpendicular to the light path therethrough. Furthermore, by making that chamber relatively large in, area in the plane normal to the light path direction, it is possible to ensure that adequate light may pass through the chamber. With these expedients, it has been found possible to form the detector 151 from a simple photometric device without recourse to the use of photomultipliers or the like.

At time periods when there is catholyte in electrolyser 26, where it is not required to operate the electrolyser, it is desirable that the anode and cathode be subjected to a potential difference thereacross of a sufficient value to prevent copper on the cathode from being etched by the catholyte. It has been found that the satisfactory results can be achieved using an additional electric source such as the source 137 shown which, during such periods, is coupled across the anode and cathode. Source 137 may provide 5 volts potential across the anode and cathode and have a capacity of approximately 10 amp. Control of application of the two sources 130, 137 to the electrolyser 26 is effected under control of the copper detector and command unit 132, operating a switch 150 as desired to effect switching of the sources to the electrolyser.

3ecause of loss of ammonia from the catholyte due to evaporation or drag-out on articles removed from the catholyte after etching, it is necessary to provide some means for replenishing the ammonia content of the catholyte. In figure 1, an ammonia replenisher tank 180 is shown together with pump ?3 operable, under control of a timer 182 to periodically add ammonia to the catholyte in tank 10. It is the case that the light absorbance of the catholyte is influenced by the ammonia content. Accordingly, for repeatable performance of the unit 132, the catholyte should be replenished before measurements of copper content are taken by unit 132. The effect of insufficient ammonia is that not all of the copper will be present in the catholyte in the form of the [Cu(NH₃)₄]⁺⁺ complex and, if an amount of ammonia is present which is less than sufficient to cause substantially all the copper to be in this form, light absorbance will increase with ammonia addition until that condition is reached. After that condition is reached, further additions have not been found to increase absorbance. Thus, it is possible to control the ammonia replenishment by the unit 132, by causing pump P3 to initiate replenishment and using the unit 132 to detect the condition where, notwithstanding further ammonia replenishment, the light absorbance of catholyte passing therethrough remains unchanged. Figure 7 illustrates circuitry in unit 132 for this purpose. As catholyte flows through the flow device 136, the signal detected by. detector 151 is passed to a sample and hold circuit 185. Samples from sample and hold circuit 152 are then passed, on the one hand, directly to a comparator 134, on the other hand, to a memory 186. The comparator would then operate to compare each fresh sample from the circuit 182 with the preceding one held in memory 186 and generate a control signal at its output in accordance with whether two consecutive samples had the same value. The arrangement would then be that, periodically, the ammonia replenisher 180 would be operated to effect a series of dosings of the catholyte, the light absorbance of the catholyte then being measured after each dosing described in relation to figure 7, ammonia replenishment being ceased on detection of two consecutive like light absorbances or after a predetermined time lapse from such detection. The addition may alternatively be made as a single dosing, continued until two consecutive like light absorbances are detected or until a predetermined time thereafter. The control signal from the comparator would thus control the pump P3 to cease replenishment at that time.

The described arrangement has been found to be particularly advantageous in use. By arranging time 182 to automatically initiate ammonia replenishment at predetermined time intervals, the unit 132 can be caused to then operate to bring about desired adjustment of the ammonia content gf the catholyte, whereafter unit 132 may automatically effect any necessary operation of electrolyser 26. Thus, substantially automatic control of the composition of the catholyte may be attained.

The arrangement of the heat exchanger 124 in the circulation path for anolyte has been found to be particularly advantageous. In practice, considerable heat may be generated in the electrolyser 25 and, since operation of the catholyte is dependent upon maintenance of proper temperature conditions, the ability to extract heat from the electrolyser and thus from the catholyte by heat exchange from the catholyte to the anolyte and thence from the heat exchanger 124 facilities maintenance of proper operating conditions. If necessary, heat sensitive devices may be employed to regulate heat extraction in the heat exchanger 124.

While the described arrangement has been detailed in relation to the use of one particular catholyte, namely ammoniacai copper chloride, the describedapparatus and methods are equally applicable to etchant systems using other etchants. More particularly the invention is applicable to arrangements using the following known etchants: acidic cupric chloride, ammonium persulphate, peroxo-sulpuric acid, ferric chloride, chromic acid.

In the described arrangement, the unit 132 operates to adjust the quantity of added ammonia by detecting a condition where addition of ammonia does cause variation in the light absorbance of the catholyte. Of course, it would be possible to effect this result by other means, such as by arranging the unit 132 to directly measure the pH of the catholyte.

These and many other modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An electrolyser for use in recovery of etched material from a liquid etchant, comprising a substantially closed or closable vessel with cathode and anode electrodes positioned therewithin, sεid vessel being provided with inlet and outlet means for flow of said etchant through the vessel, said electrodes being positioned whereby in use to effect deposition of said etched material on one of said electrodes when said etchant is passed through the vessel and electric potential is applied across said electrodes.

2. Etching apparatus of the kind in which material to be etched is subjected to chemical action by liquid etchant wherein an electrolyser is provided for recovery of etched said material from the etchant by electro-deposition of the etched manerial, said electrolyser being the form of a substantially closed or closable vessel with cathode and anode electrodes positioned therewithin, said vessel oeing provided with an inlet and an outlet, pump means being provided for effecting flow of said etchant through the vessel from said inlet to said outlet whereby on application of an electric potential to said electrodes, when said etchant is passed through the vessel, said etched material is deposited on one of said electrodes.

3. Etching apparatus as claimed in claim 2 wherein said pump means is arranged to effect said flow from an etchant retention chamber which recovers etchant after contact with said material to effect etching.

4. Etching apparatus of the kind in which material to be etched is subjected to chemical action by a liquid etchant, wherein means is provided for detecting the quantity of said material in the etchant and operable to electrolytically deposit out of the etchant at least a portion of the material in the etchant on detection of an excess of said material in the etchant.

5. Etchant apparatus of the kind in which material to be etched is subject to chemical action by a liquid etchant, having means for detecting the quantity of said material in the etchant, said means comprising means operable to pass the etchant through a narrow passageway, means for directing light through etchant flowing through said passageway, and means for detecting the amount of light so passing through the etchant whereby to provide an indication of said quantity in accordance with the light absorbance of the etchant.

6. Etchant apparatus as claimed in claim 5 wherein detecting means is connected to operate the electrolyser, under circumstances where the light absorbance is detected as being, indicative of increase of the quantity of said material in the etchant above a predetermined level, whereby to reduce the quantity to a level below said predetermined level.

7. Etching apparatus as claimed in claim 5 wherein said passageway is narrow in the direction of passage of said light but wide in the direction normal thereto.

8. Etching apparatus of the kinα in which material to be etched is subjected to chemical action by a liquid etchant, wherein means is provided for monitoring the content of at least one component of the etchant and effective to add to said etchant a quantity of said component when the concentration thereof falls below a predetermined level.

9. Etching apparatus of the kind in which material to be etched is subjected to chemical action by a liquid etchant wherein means is provided for effecting an addition operation for adding to said etchant, either in a single continuous dosing or by a plurality of individual dosings, a component thereof which in use of the apparatus tends to be depleted, the apparatus being arranged whereby in use during said adding operation, a property of said etchant is monitored and determinations are made as to whether that property has been altered as compared to a preceding determination.

10. Etching apparatus as claimed in claim 9 arranged whereby said addition operation is ceased after said property is found no longer to be altering.

11. Etching apparatus as claimed in claim 9 or claim 10 wherein said physical property is light absorbance of the etchant.

12. Etching apparatus as claimed in claims 9 or claim 10 wherein the light absorbance of the etchant at a particular wavelength or band of wavelengths is property of the etchant which is determined.

13. Etching apparatus as claimed in any one of claims 9 to 12 arranged wherein addition of said component is initiated automatically.

14. An electrolyser for recover of etched Material retained in a liquid etchant, said electrolyser comprising a vessel having cathode and anode electrodes therein, a barrier dividing the interior of said vessel into two portions, one containing the Cathode electrode and the other containing the anode electrode, such that liquid communication between the interior portions otherwise than through the barrier is in use precluded, said vessel being arranged for reception of said etchant in said one interior portion and for reception in said other interior portion of an anolyte liquid, said barrier being porous whereby to permit said anolyte liquid to pass therethrough but such as to preclude said material or at least some form thereof from passing therethrough; said etchant and said anolyte liquid in use providing an electrically continuous medium between said electrodes such that, on application of electric potential across said electrodes, said material is deposited. by electrolytic action on said cathode.

15. An electrolyser as claimed in claim 14 wherein said electrolyser is. closed or closable.

16. An electrolyser as claimed in claim 14 or claim 15 arranged to circulate said etchant containing material through said one interior portion.

17. An electrolyser as claimed in claim 16 arranged to circulate said anolyte liquid through said other interior portion.

18. An electrolyser as claimed in any one of claims

14 to 17 wherein said barrier is designed to be impervious at least to Cu⁺ ions. 9. A method of recovery of etched material from a liquid etchant comprising passing the liquid etchant through a substantially closed vessel so as to contact cathode and anode electrodes positioned within the vessel, and applying an electric potential across said electrodes whereby to remove said etched material from said etchant by electrolytic action.

20. A method of etching material by subjecting the material to chemical action by a liquid etchant characterised by the step of recovering the etched material from the etchant by the method defined in claim 13.

21. A method of etching in which material to be etched is subjected to chemical action by liquid etchant, including the step of detecting the quantity of said material in the etchant and electrolytically removing from the etchant at least a portion of said material in the etchant on detection of an excess of said material in the etchant.

22. A method of etching in which material to be etched is subjected to chemical action by a liquid etchant, including the step of detecting the quantity of said material in the etchant by passing the etchant through a narrow passageway, directing light through the etchant passing through said passageway, and detecting the amount of light so passing through the etchant, thereby providing an indication of said quantity in accordance with the light absorbance of the etchant.

23. A method of etching in which material to be etched is subjected to chemical action by a liquid etchant, including the step of monitoring the content of at least one component of the etchant and adding to said etchant a quantity of said component when the concentration thereof falls below a predetermined level.

24. A method of etching in which material to be etched is subjected to chemical action by a liquid etchant, including the steps of adding to said etchant a component thereof which is in use depleted, making a plurality of time spaced measurements of a property of said etchant, and terminating said addition pursuant to said measurements showing said property to be substantially unchanged.

25. A method of recovery of etched- material retained in a liquid etchant, comprising positioning the etchant containing the material as well as an anolyte liquid in a vessel such that these are divided one from the other by a barrier which is porous whereby to permit said anolyte liquid to pass therethrough but such as to preclude said material, or a form thereof, from passing therethrough, and subjecting the said. etchant and said anolyte liquid tα an electric potential by means of electrodes, a respective one positioned in each, whereby to effect removal of said material from said etchant bγ electrolytic action.

26. Etching apparatus substantially as herein described with reference to the accompanying drawings.

27. An electrolyser substantially as herein, described with reference to the accompanying drawings.

28. A method of etching substantially as herein described with reference to the accompanying drawings.