CN1633521A - Precious metal recovery - Google Patents

Abstract

Various methods have been proposed to separate precious metal from a fluid utilized for plating. The known methods and devices are complicated and expensive. To overcome this problem, a method and a device for plating work pieces with a fluid containing at least one precious metal are provided. According to the invention the work pieces are contacted with the fluid and the fluid is filtered, after use, through at least one ceramic membrane filter in order to separate the at least one precious metal from the fluid. According to the invention a ceramic membrane filter having an exclusion pore size in excess of 10,000 Dalton is utilized.

Description

Recovery of Precious Metals

                      

The invention relates to a method and a device for coating workpieces with a liquid containing precious metals. The invention is particularly suitable for use in processes for producing circuit carriers.

When plating a workpiece, if its surface is non-conductive, it must first be treated with a conductive treatment. To do this, the workpiece is immersed in a solution containing ionic, ionized or colloidal palladium. More specifically, ionic palladium can exist in the form of a salt, such as palladium chloride, which is usually dissolved in a hydrochloric acid solution. Ionized palladium exists in the form of complexes, such as ammonium pyridine complexes. Colloidal palladium may contain various protective colloids, such as those formed from tin(II) chloride or those composed of organic polymers. Palladium adsorbed on the surface of the workpiece acts as, for example, an activator to cause electroless metal deposition, thereby forming a conductive layer on the surface, after which any metal can be plated on the surface. This method is used to manufacture printed circuit boards and other circuit carriers as well as, for example, metal-plated parts in the sanitary equipment, automotive and furniture industries, for example more specifically chrome-plated plastic parts.

Palladium-containing solutions can also be used to form the conductive layer. In the direct plating method, other metals are deposited electrolytically after palladium treatment without previously forming a metal layer by electroless metal coating.

During the treatment of workpieces having non-conductive surfaces, parts of the palladium-containing solution remain attached to the workpiece when the previously impregnated workpiece is removed from the solution. The attached solution is generally washed with water.

Known activation methods, for example, use colloidal palladium, typically a solution containing 50-400 mg/l of palladium. When processing plastic parts with a geometric surface of one square meter, about 5-10 mg of palladium is usually absorbed. This amount is necessary for the activation of the plastic surface. When the workpiece to be treated leaves the corresponding processing point, about 0.2 liters/square meter of the activation solution is carried away from the bath and remains on the surface of the workpiece. Consequently, about 10-50 mg of palladium is lost to the bath as the attached solution is carried out of the process bath, after which these solutions are washed off and transferred to the waste water treatment process.

Palladium-containing solutions can also be utilized in direct electroplating of non-conductive surfaces without electroless metal plating. In these cases, a high concentration of palladium (eg 400 mg/L) is required in the solution.

When using known direct metal plating methods, the amount of palladium carried over by the processing solution is about 50 mg/m2. By taking appropriate measures (such as pre-absorption of polyelectrolyte compounds on non-conductive surfaces), the absorbed palladium particles can be increased from very low values up to 50 mg/m2 workpiece surface. Even so, 60-70% of the palladium used in the solution was lost to carryover. Only 40-30% is actually used as the plated metal on the workpiece surface.

Examples of palladium recovery from process solutions are known. For example, US Patent No. 4,078,918 describes a recovery method, such as palladium, from a variety of materials containing dissolved or non-dissolved palladium. The material is first treated with an oxidizing agent to destroy possible organic components, and then with ammonium hydroxide to form amine complexes. The palladium complex thus obtained is then reduced with ascorbic acid, and palladium is deposited in metallic form from the working fluid and can be filtered.

In addition, in "Reclamation of Palladium from colloidal seedersolutions" in Chemical Abstracts, 1990: 462908 HCAPLUS "Reclamation of Palladium from colloidal seedersolutions" describes a method of colloidal Pd/SnCl _before electroless metal plating. The palladium was recovered as a pretreatment in which air was passed through the solution for 24 hours to flocculate the palladium. The sediment is separated, dried and further processed.

In Chemical Abstracts, 1985: 580341 HCAPLUS's "Recovering Palladium and Tin Chloride from the Waste Liquid of Colloidal Palladium in Tin Chloride" describes a method of precipitating palladium by adding metal tin at 90°C.

US Patent No. 4,435,258 discloses another method of recovering palladium from depleted baths used to activate non-conductive surfaces that are subsequently used as an electroless metal plating process. The activation solution is reprocessed by adding an oxidizing agent such as hydrogen peroxide to oxidize colloidal palladium into solution, heating the solution to destroy residual hydrogen peroxide, and electrodepositing palladium from this solution onto the cathode .

In Chemical Abstracts, 1976: 481575 HCAPLUS's "Recovery of Colloidal Palladium in the Waste Liquid of Activation _Solution for No-current Metal Coating Resin Surface", finally described a method of obtaining palladium by Pd/SnCl, wherein palladium Precipitate by addition of concentrated nitric acid and filter.

DE 100 24 239 C1 describes a method for coating workpieces with palladium colloidal solutions by bringing the workpieces into contact with the colloidal solution, according to which palladium is recovered by separating palladium colloidal particles from the colloidal solution after use through a membrane filter palladium. Materials such as those made of ceramics can be used for filtration. The exclusion pore size of the membrane is from 200 to 10,000 Daltons. It is mentioned that palladium particles pass through the membrane filter when the exclusion pore size of the membrane exceeds 10,000 Daltons.

Prior art methods of plating workpieces using palladium colloidal solutions are complex and expensive.

The basic problem addressed by the present invention was to overcome the disadvantages of the known methods and to find a method which can be carried out at low cost by coating workpieces with liquids containing at least one noble metal. Using the method described should only require the addition of small amounts of chemicals. Furthermore, the described method consumes little energy, requires only a short time and is particularly low-maintenance.

This problem is overcome by the method of claim 1 and the device of claim 15 . Preferred embodiments of the invention are given in the dependent claims.

The method according to the invention for coating a workpiece with a liquid containing at least one noble metal comprises bringing the workpiece into contact with the liquid. For the recovery of precious metals from a liquid, the precious metals are separated from the liquid by filtering said liquid through at least one ceramic membrane filter, the exclusion pore size of which exceeds 10,000 Daltons, after coating the workpiece with said liquid . The precious metals are separated from the liquid by filtration.

Plating refers to any treatment aimed at modifying the surface of a workpiece using a liquid, which must contain a precious metal. However, processes for coating workpieces with polymer coatings, in particular enamelling, are not included therein.

The workpieces to be plated include metal workpieces, non-metallic workpieces and workpieces composed of metal and non-metallic materials. The workpiece can have all imaginable forms and serve all imaginable purposes. Preferred workpieces are semi-finished products for the production of circuit carriers, more particularly for the production of printed circuit boards and hybrid circuit carriers such as multi-chip modules.

Noble metals which can be separated from the corresponding liquids are all elements of Groups 1 and VIII of the Periodic Table of the Elements, ie in particular Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag and Au. The invention preferably relates to a method of treating a workpiece by plating with a palladium-containing liquid.

More particularly, the liquid may be a solution. This is especially true when the noble metal is present in ionic or ionized form. By noble metal in ionic form is meant more specifically a noble metal salt dissolved in water or in another solvent which facilitates the dissociation of the salt. By noble metal in ionized form is meant noble metal complexes, more specifically noble metal complexes with organic complexing ligands. The complexes can be uncharged or in ionic form. The liquid may exist in the form of a colloid, in particular a colloid of elemental noble metals.

The precious metal-containing liquid can be a processing fluid or a cleaning fluid for processing workpieces. The processing liquid refers to a liquid that changes the surface properties of a workpiece, such as a coating liquid, including an activation liquid, a cleaning liquid, an etching liquid, or the like. In contrast, the function of the cleaning fluid is only to remove the machining fluid still attached to the surface of the workpiece after treating the workpiece with the machining fluid.

After the workpiece has been coated with the liquid, the precious metal is filtered through at least one ceramic membrane filter. That is to say, the liquid is first used to coat workpieces, and the subsequent filtration is only to recover the precious metals contained therein. The liquid may contact the workpiece by, for example, spraying, jetting, flooding or blasting, collecting the liquid dripping from the workpiece and immediately treating it with a membrane filter. However, it is also possible for the collected liquid to initially remain in the storage tank and thus be returned to the workpiece. In this case, the liquid can be fed to the membrane filter after collection for a period of time (discontinuous method), or part of the liquid can be continuously diverted from the storage tank and transferred to the membrane filter (continuous method). In this case, in order to keep the storage tank in a stable full state, the amount of fresh processing fluid introduced into the storage tank per unit time is kept equal to the amount of liquid passing through the membrane filter per unit time. The workpiece may also be brought into contact with the processing fluid by immersing the workpiece in a processing vessel containing the processing fluid. In this case, the used processing fluid can be collected for a period of time and introduced into the membrane filter (discontinuous method), or part of the liquid can be continuously diverted from the storage tank and transferred to the membrane filter (continuous method).

The method of the invention is simple and easy to implement, and its chemical consumption and energy consumption are very small, saves time, and has low requirements for maintenance. The method of the invention can continuously separate precious metals from waste liquid of processing fluid. More particularly it allows the regeneration of the spent processing fluid after separation of the palladium-containing fraction so that all the palladium can be recycled to the treatment process.

With Chemical Abstracts, described in 1990: 462908 HCAPLUS from colloidal Pd/ _SnCl The method for reclaiming palladium compares, the advantage of the inventive method is that the part containing palladium is separated thoroughly, but in the precipitation method described in Chemical Abstracts A non-negligible portion of palladium is oxidized to the divalent state (soluble state of palladium), so palladium cannot be completely separated from the solution by filtration. Therefore, this part of palladium cannot be recovered and is lost.

Another advantage of the method of the present invention over the method described in Chemical Abstracts, 1985:580341 HCAPLUS is that it does not need to consume a large amount of other chemicals (like metallic tin), energy and time as required for heating the colloidal solution in the known method .

The method according to the invention also has a substantial advantage over U.S. Patent No. 4,435,258 in that palladium can be almost completely removed from solution, whereas according to U.S. Patent No. 4,435,258 only very low current efficiencies can be achieved, especially when palladium When the concentration is low (after long-term electrolysis). Therefore, the complete removal of palladium is very complicated or impossible using current technology.

Compared to the method described in Chemical Abstracts, 1976: 481575 HCAPLUS, the method and apparatus according to the invention are particularly suitable for continuous operation, moreover, the method in said publication must use other chemicals.

Mentioned in German Patent 100 24 239 C1, when the exclusion pore size of the membrane filter obviously exceeds 10,000 Daltons, the palladium particles in the colloidal palladium colloid solution will pass through the filter, surprisingly, in the present invention exclude Ceramic filters with a pore size of eg 20,000 Daltons still have excellent separation performance for colloidal palladium. In this regard, reference is made to Experiments 1 and 2 of Example 1.

Compared with known methods and devices, the method and device according to the invention have the following advantages:

a. Precious metals (especially palladium) can be recovered from ionized, ionized and colloidal solutions using only one device. It does not require the use of several matching devices. As a result, solutions can be mixed and collected prior to regeneration. The same applies to machining fluids and cleaning fluids: machining fluids containing high concentrations of precious metals can be mixed with cleaning fluids containing very low concentrations of precious metals and then processed together.

b. Because a large-pore ceramic membrane filter can be used to successfully separate precious metals, a ceramic membrane filter with better resistance to chemicals and temperature effects can be used. Maintenance requirements are greatly reduced as the filter does not require frequent cleaning. Ceramic membrane filters also have a long service life. In addition, noble metals are not adsorbed on the membrane material.

c. The reprocessing of the liquid to be treated is simple and easy. For example, it does not need to be performed under a protective atmosphere to prevent the colloidal particles from dissolving in the liquid.

Colloidal activators based on palladium consist of palladium particles surrounded by a protective coating (protective gel). Examination using high resolution transmission electron microscopy (HTEM) and atomic force microscopy (AFM) showed palladium particles to be at least 2.5 nm in diameter. The average particle diameter is 4 nm, consistent with the Gaussian distribution of particles. A broad particle size distribution (2 to 18 nm) from particles with a maximum size of 18 nm to smaller particles was found by examining the cleaning solution obtained after treating the workpiece with the colloidal activator.

In practice, colloidal solutions are acidic (often containing large amounts of hydrochloric acid), contain chloride ions, and may also contain tin in oxidation state ((II) and (IV)) or organic, polymeric stabilizers (like gelatin or poly vinylpyrrolidone) and reducing agent. With the exception of polymers (which are used in small amounts), all other substances contained herein are ionic. These ionic constituents are believed to be much smaller than the palladium particles.

Surprisingly, although in the case of tin-containing colloidal solutions (i.e. together with high concentrations of tin (typically more than 70 times the palladium concentration)) and tin compounds are known to form colloidal solutions that are not easily filterable, palladium particles can still Very selective and complete removal from these colloidal solutions is achieved by using suitable membrane filters comprising different porosities.

For ultrafiltration, various membranes made of various materials have been tested. Tests have shown that when selecting a membrane filter it is important that the selected membrane filter is sufficiently stable for noble metal-containing liquids, which may contain, for example, 15% by weight of hydrochloric acid.

For the separation of palladium colloidal particles, a ceramic membrane filter having an exclusion pore size of about 15,000 Daltons to about 25,000 Daltons, preferably a ceramic membrane filter having an exclusion pore size of about 17,500 Daltons to about 22,500 Daltons may be utilized , and a ceramic membrane filter with an exclusion pore size of approximately 20,000 Daltons is most preferred.

Preferably the ceramic membrane filter used is made of a ceramic material containing aluminum oxide (in particular α-Al ₂ O ₃ ), titanium dioxide and possibly haloia. In theory, other filter materials could also be used. Typically, the filter material is deposited on a highly porous support that provides the filter with the required mechanical stability. The support may consist of, for example, α-Al ₂ O ₃ or SiC (silicon carbide).

The shape of the filter can be disc or tube. In the first case, the flow of liquid is directed towards the disc, substantially perpendicular to its surface, the flow of liquid exiting radially. There is a pressure differential between the two disk surfaces so that the permeate can penetrate the disk. If the filter has the shape of a tube through which the liquid is conveyed axially, a pressure exists between the inner space and the outer space of the tube. As a result, permeate can permeate the tube wall, eg from the inner space of the tube into the outer space of the tube. This second method is called dynamic filtering. In this case, the noble metal remains in the inner space of the tube, while the substantially noble metal-free liquid permeates from the inner space of the tube to the outer space of the tube through the tube wall.

Some fluids can be filtered directly without any additional pretreatment. In this case excellent results were obtained using ceramic membrane filters.

In some cases, the fluid to be reprocessed is first chemically pretreated. For this purpose, said liquid is mixed with a suitable chemical substance to alter at least one precious metal contained therein, before being filtered through a membrane filter after having been used for plating, so that the precious metal remains substantially completely upon filtration . It is assumed that by adding these chemicals, the particle size of the precious metal is changed so that the particles containing the precious metal can no longer pass through the pores of the membrane filter. For this purpose, it should be sufficient to adjust the average particle size to values exceeding about 10 nm when the particle size follows a Gaussian distribution. In this case, membrane filters with exclusion pore sizes exceeding 10,000 Daltons have been able to retain almost all of the precious metals in the concentrate. Larger particles can thus be produced by adding these chemicals when using membrane filters with larger exclusion pore sizes.

If palladium is present in the solution in ionic and/or ionized form, said liquid may be mixed with a chemical substance selected from the group consisting of reducing agents, sulfur compounds, selenium compounds and hoof compounds. Pretreatment chemicals are preferably selected from boron hydride, amine borane, hypophosphite, inorganic sulfide and organic sulfur compounds, especially alkali metal and ammonium dimethyl dithiocarbamate, sulfide, hydrogenated Boron (such as tetrahydroborate) and hypophosphite. The organosulfur compound is more specifically an organic compound in which sulfur is bonded to one or two carbon atoms to form a single or double bond, i.e., for example mercaptans, sulfides, disulfides and polysulfides, sulfamides and thial.

If the palladium is present in the liquid in colloidal form, a pH adjuster is used as the chemical substance, and the fluid is mixed with the pH adjuster so that the pH ranges from 3 to 12.

In both cases above, a solution is obtained which is very suitable for the separation of noble metals, in this case palladium.

The following advantages result from the improvement of the present invention:

a. Preprocessing is very simple. It is sufficient to mix the precious metal-containing liquid with the desired substance or with the pH regulator, respectively.

b. Consume very little other chemicals. To process 200 liters of wash water (7 mg/l palladium) resulting from the treatment of organopalladium complexes, only 7.5 ml of a solution containing 467 g/l sodium dimethyldithiocarbamate was required. If it is desired to process the cleaning water produced by the treatment of palladium colloid (organic protective colloid, 25 mg/liter Pd), as long as 0.5 liter of 432 g/liter NaOH aqueous solution is sufficient.

From the observation and test of the present invention, it can be seen that it is feasible to recover precious metals from cleaning fluid and/or processing fluid through membrane filter. to this end

a. Contact the workpiece with palladium-containing processing fluid,

b. Then, the machining fluid still attached to the surface of the workpiece is removed with a cleaning fluid, and

c. Pass the processing fluid and/or cleaning fluid through (preferably under pressure) at least one ceramic membrane filter for filtration, the liquid passing through the at least one ceramic membrane filter is the permeate, and does not pass through the at least one ceramic membrane filter The liquid in the membrane filter is the concentrate.

After treatment with a palladium-containing liquid, the workpiece (preferably made of a non-conductive material) is kept as small as possible in a suitable device by immersing the workpiece (preferably made of a non-conductive material) in the cleaning solution, flooding it with the cleaning solution or preferably spraying the cleaning solution onto said workpiece. volume of cleaning solution. Next, the cleaning solution is passed by means of a pressure pump through a ceramic membrane filter, which retains the palladium particles and allows the cleaning solution to pass through. The permeate is then transferred to a wastewater treatment process.

Process fluids and/or cleaning fluids may be mixed with chemicals such as reducing agents, sulfur compounds, selenium compounds, tellurium compounds, or pH regulators prior to treatment with membrane filters.

In a particularly preferred embodiment of the invention, only the cleaning liquid or the cleaning liquid which preferably contains at most 5% by volume of the processing liquid is treated with a membrane filter (preferably under pressure). The workpiece is contacted with fresh cleaning solution, and the fresh cleaning solution is continuously provided in a predetermined amount per unit time. More preferably, the amount of penetrating liquid formed per unit time can be adjusted to be approximately equal to the amount of cleaning liquid contacting the workpiece per unit time. As a result, quiescent conditions are achieved in the processing plant: the amount of fresh cleaning fluid delivered to the workpiece is exactly the same as the amount of permeate flowing out of the device, resulting in a stable flow. Of course, such a state can only be achieved if the amount of chemical species added is negligible and there are no other influencing factors. In fact, the evaporation of the cleaning fluid can become a major part.

The remaining palladium in the form of a concentrate of a homogeneous dispersion of the metal or metal compound (eg as a PdS dispersion) can be recovered. The remaining palladium can, for example, be dissolved, converted to palladium chloride and used to synthesize new palladium-containing process fluids or for other purposes. The palladium-containing concentrate can also be concentrated to almost dryness in a filter press. For this purpose, the concentrate from the membrane filter is introduced into a vessel in which the palladium-containing slurry formed during the concentration process is deposited and the resulting suspension slurry is introduced into a filter press. The palladium-containing filter cake obtained from the filter press can be used as a base material for the manufacture of pure palladium and palladium compounds.

In an apparatus according to the invention for coating a workpiece with at least one noble metal-containing liquid, means for bringing the workpiece into contact with the liquid and means for clamping the workpiece are generally provided.

The means for bringing the workpiece into contact with a liquid can be, for example, a spray head that sprays, jets, floods or releases a machining or cleaning fluid onto the surface of the workpiece. Such an arrangement is often required, for example, when a high flow rate of liquid is required to reach the surface or when the amount of liquid required needs to be minimized. In another embodiment of the present invention, the contacting device used is a treatment vessel containing a machining fluid and into which the workpiece is immersed.

The device for clamping the workpiece can also be in various forms: for example, the workpiece can be clamped in the traditional way of clamps, screw clamps, tongs or screw fixing. In addition, workpieces can also be clamped, transported and handled in a horizontal position simply on or between rollers, wheels or cylinders.

In addition to the aforementioned features, the plant also includes means for separating at least one precious metal from the liquid. This facility includes at least one ceramic membrane with an exclusion pore size exceeding 10,000 Daltons. The facility also includes at least one pump for delivering said liquid to said at least one ceramic membrane and a liquid conduit for directing said liquid to said at least one ceramic membrane from means for bringing said workpiece into contact with liquid. The pump may also be any pump that does not use a motor or pumps that delivers fluid by gravity only.

According to the explanations provided above, the facilities for separating precious metals from liquids are also provided with mixing facilities. In this mixing facility, a liquid from a liquid-to-workpiece contacting device can be mixed with chemicals. For this purpose, any conventional mixing means known in chemical reaction technology can be used, such as stirring means and mixing zones in fluid reactors.

Furthermore, the plant for separating precious metals from a liquid provides a multiphase separation unit in which the slurry produced during the separation and coming from the plant for separating said at least one precious metal from said liquid can be settled. Such multiphase separation units are formed, for example, by settling tanks in which substantially no convection of liquids takes place. The suspension slurry can then be directed to a filter press to substantially purify and dry the predominantly precious metal containing slurry.

The present invention will be further described below in conjunction with the accompanying drawings. More specifically,

Figure 1: a schematic perspective view of a ceramic membrane filter;

Figure 2: is a schematic diagram of a workpiece coating device according to the present invention.

FIG. 1 depicts a ceramic membrane filter in the form of a tube 1 . The tube uses a support tube 3 made of a highly porous ceramic material, here alumina. A further oxide ceramic layer is provided as membrane filter layer 2 on the inner side of the support tube 3 . The membrane filter layer 2 is sequentially composed of two layers ₍ not explicitly shown), namely a first microfiltration layer made of α- _Al2O3 and a second ultrafiltration layer made of _ZrO2 and _TiO2 , The pore size of _TiO2 is very small such that filtration is still feasible for an exclusion pore size of eg 20,000 Daltons. The exclusion pore size of the membrane filter layer 2 is about 20,000 Daltons. Therefore, the average pore size is about 20 nm.

The inner diameter of the tube is about 6 mm. The tube length is about 1000 mm. Fluid under pressure flows in the direction marked 4. The pressure difference between the inlet and outlet of the tubes ranges from 1.5 to 3 bar.

In order to collect the permeate passing through the inner wall of the tube, the ceramic tube is placed in another tube concentrically.

The lower half of FIG. 2 comprises two filters 1 shown in FIG. 1 , which are ceramic tube parts with several bore holes in the form shown in FIG. 1 . For this purpose, for example 19 axial boreholes are drilled in a ceramic tube consisting of a highly porous ceramic material, the axial boreholes being parallel.

In the upper part of FIG. 2, the processing area of the printed circuit board processing device is partially shown. The printed circuit boards are conveyed continuously in the process direction R through the different process zones. A typical example of this method is described inter alia in WO 93/17153 A1.

After a pretreatment step, the printed circuit board (not shown) is immersed in an activation bath containing colloidal palladium in the activation zone A-pd. For this purpose, the liquid is contained in a immersion bath.

Then, the printed circuit board is conveyed through three successive cleaning zones S ₁ , S ₂ and S ₃ . Here, the activation solution attached to the surface of the printed circuit board is continuously washed off. For this reason, spray heads are provided in different cleaning areas S ₁ , S ₂ and S ₃ . The cleaning zones S ₁ , S ₂ and S ₃ are configured as open-top containers with spray heads arranged on the walls of their long sides. In order to wash away the adhering activation solution, when the printed circuit board is sunk and/or lifted out of the cleaning areas S ₁ , S ₂ and S ₃ , the cleaning solution is sprayed on the surface of the circuit board. The cleaning solution is collected at the bottom of the containers in the cleaning areas S ₁ , S ₂ and S ₃ respectively. Fresh cleaning liquid is distributed at an average flow rate of 200 l/h into the cleaning zone _S3 , from which it is directed in the opposite direction to the printed circuit board processing direction R to the cleaning zone _S2 arranged upstream of it, from which it is led to the cleaning zone S ₁ , the flow rate remains the same. Each of the cleaning areas S ₁ , S ₂ and S ₃ is also configured with a collection tank (not shown), in which the cleaning liquid is collected respectively. The collected cleaning solution is discharged from the collection tank of cleaning zone _S1 for further processing at a flow rate of 200 liters/hour.

After the surface of the printed circuit board is cleaned to remove the adhering activation solution, it is post-treated. Such processing fluids are, for example, sulfinic acid solutions. In post-treatment zone B, the printed circuit boards are treated by immersing them in a solution contained in a treatment vessel.

Afterwards, the attached post-treatment liquid is washed away in the cleaning zones S ₄ , S ₅ and S ₆ . Likewise, the cleaning liquid is sprayed onto the surface of the printed circuit board by the spray heads disposed in the cleaning areas S ₄ , S ₅ and S ₆ . The collected cleaning solution is collected into a collection tank (not shown), thereby being continuously introduced in the direction opposite to the processing direction R of the printed circuit board into the cleaning zones S ₅ and S ₄ arranged upstream thereof. The cleaning solution is discharged from the cleaning area _S4 and immersed in the subsequent wastewater treatment process.

Next, the printed circuit board is immersed in the etching solution in the container of the etching area C-Pd. Here, palladium absorbed to the copper surface is removed by activation by slightly etching the copper surface. In this case as well, the printed circuit board is immersed in an etching solution.

Afterwards, the adhering processing fluid is washed off the surface of the printed circuit board again. For this, the printed circuit boards are conveyed to the cleaning zones S ₇ , S ₈ and S ₉ . The etchant attached to the surface of the printed circuit board is removed by the cleaning solution sprayed on the surface of the printed circuit board from the nozzle. To this end, fresh cleaning fluid is introduced at a flow rate of 200 liters/hour into cleaning zone _S9 , where the cleaning fluid collected is collected in a collection tank (not shown). Likewise, the collected cleaning solution is introduced from the cleaning zone S ₉ into the cleaning zone S ₈ along the direction opposite to the processing direction R of the printed circuit board, and then enters the cleaning zone S ₇ . From the cleaning zone S ₇ , the palladium-rich cleaning solution is introduced into the regeneration unit at a flow rate of 200 liters/hour.

The aforementioned way of handling the printed circuit board is just one possible option. Printed circuit boards are also processed in so-called horizontal installations. The circuit boards are thus conveyed in a horizontal direction and pass through the respective processing zones in a horizontal or vertical orientation. In the different processing zones, the liquid is delivered to the surface of the printed circuit board by means of spray heads.

The cleaning liquid produced by cleaning zone _S4 is substantially free of precious metals and can be distributed to conventional wastewater processing systems. In contrast, the cleaning solutions produced by cleaning zones _S1 and _S7 contain palladium, which are regenerated in the manner according to the invention:

First, various washing waters are collected in the buffer tanks 11.1 and 11.2 respectively. The cleaning solution is discharged from the buffer tanks 11.1 and 11.2 at a flow rate of 200 liters/hour, and then guided to the conduits 13.1 and 13.2 by the pumps 12.1 and 12.2 respectively, and delivered to the common conduit 13.3. To adjust the pH, the combined washes (if required) were mixed with a pH adjuster (here NaOH). To this end, NaOH solution is added from storage tank 14 to the combined cleaning solution. Dosing of NaOH solution was controlled using an electronically controlled pathway (not shown). The control path includes a pH probe 15 (eg a pH measuring electrode) to control a dosing pump of NaOH solution. In cases where the pH of the cleaning solution is close to 7, the pH does not need to be adjusted to the exact value of 7.

If an ionic or ionized palladium solution is used instead of the colloidal palladium solution, the pH adjuster is replaced with a solution of another suitable chemical substance, which is added to the liquid stream to allow filtration of the palladium-containing liquid.

Then, the cleaning solution whose pH has been adjusted to about 7 is introduced into the collection tank 16 by another pump 12.3 through a conduit 13.4.

In the collection tank 16 a low level sensor 17.1 and a high level sensor 17.2 are provided. If the liquid level is higher than the high liquid level sensor 17.2, the liquid is led from the container 16 to the pump 18 through the conduit 13.5. And if the liquid level of the collecting tank 16 is lower than the low liquid level sensor 17.1, the cleaning liquid is no longer pumped out by the collecting tank 16.

By means of a pump 18, the liquid is led through two membrane filter tubes 1 connected in series at a pressure of 1.5-3 bar. The permeate through the pipe wall is discharged to waste water treatment A. The concentrated liquid remaining in the filter tube is circulated through the closed circular conduit 13.6, thereby continuously concentrating the palladium in the liquid. Through the branch conduit 13.7, part of the concentrated cleaning solution is continuously flowed back into the collection tank 16, and thus guided to the membrane filter through the pump 18, so that the palladium content in the fluid gradually increases.

In collection tank 16, the palladium-containing slurry resulting from the concentration is deposited in a multiphase separation zone. The suspension slurry can be drained into another container 19 .

The fluid directly from the activation zone A-Pd can also be released directly for regeneration and lead to the ultrafiltration process. For this purpose, the liquid can be manually transferred via the path numbered M to the collection tank 20, or it can be guided in small quantities to the buffer tank 11.1 by means of the pump 12.4. The liquid that has been removed and manually transferred to the collection basin 20 can then be distributed to the collection basin 16 by eg another pump 12.5.

The suspension slurry in the container 16 of the multiphase separation unit is introduced into a filter press 21 to further separate palladium. The filter press 21 is shown in dashed lines in FIG. 2 . It contains filter material with a pore size of about 50 microns. The pressure in the filter press was about 4 bar. The filtered liquid can be recycled back to the collection tank 16 or distributed to the waste water treatment area A through a further conduit 22 .

The following example is used to explain the present invention:

Example 1:

For the tests, printed circuit boards were treated with a colloidal acidic activation solution containing 400 mg/l of colloidal palladium, a protective colloid in the form of a polymer and a reducing agent in the form of sodium hypophosphite. The average particle diameter of the palladium colloidal particles is about 4 nm.

After cleaning, the printed circuit board was treated with a post-treatment solution containing organic sulfinic acid, then cleaned again and finally treated in an etching solution containing 300 g/l of sodium persulfate. The palladium thus removed from the copper surface is dispensed into the etchant and enters the subsequent cleaning solution with the etchant adhering to the surface of the printed circuit board.

The cleaning liquids obtained in the cleaning zones _S1 to _S3 and _S7 to _S9 (see FIG. 2 ) under the aforementioned conditions were respectively distributed to the regeneration device at a flow rate of 200 liters/hour. Made of ceramics (α-Al ₂ O ₃ as a support material, covered with two ultra-filtration layers: ZrO ₂ and TiO ₂ , TiO ₂ has an extremely fine pore size, and the exclusion pore size of the filter is about 20,000 Dalton; TiO ₂ coated in a sol-gel method) membrane filter to filter the liquid. The concentrations of palladium in the cleaning solutions and the pH of these solutions are listed in Table 1 (Tests 1 and 2).

The pH of the liquids produced from the washing zones _S1 to _S3 and _S5 to _S7 was not adjusted using a pH regulator.

For ultrafiltration, the concentrate is passed through a ceramic membrane filter at a flow rate of 2,800 liters per hour. A permeate flow rate of 40 to 45 liters/hour was achieved.

The permeate and concentrate were obtained by ultrafiltration. The concentrations of palladium in the permeates and concentrates according to tests 1 and 2 are also listed in Table 1.

Example 2:

In another experiment, the cleaning solution from the colloidal activation solution and the cleaning solution from the etching solution were mixed in a volume ratio of 1:1 (test 3). The same ceramic membrane filter as in Example 1 was used. The initial palladium concentration in the mixed wash solution and the pH of the mixture are listed in Table 1. To adjust the pH of the mixed cleaning solution to 7, NaOH solution was added to the cleaning solution.

The palladium concentration of the permeate obtained after ultrafiltration was <0.5 mg/l. The concentration of palladium in the concentrated solution is >1 g/L (see Table 1).

Example 3:

In another trial 4, the same ceramic membrane filter as in Example 1 was used. The colloidal activation solution was added to the cleaning solution mixture obtained in Example 2 at a volume ratio of 1:100. The palladium concentration in this liquid is equal to 15.0 mg/l. The pH of the liquid was adjusted to 7 using NaOH solution. The palladium concentrations in the permeate and concentrate after ultrafiltration are listed in Table 1.

Example 4:

In another experiment 5, the same ceramic membrane filter as in Example 1 was used. An inorganic activator solution was used in this test instead of a colloidal activator solution. The activator contains an organic palladium complex (Neoganth® Activator, Atotech Deutschland GmbH, Germany), and the palladium concentration in this solution is 250 mg/L.

The printed circuit board activated by this solution is then cleaned again through three cleaning zones S ₁ , S ₂ and S ₃ , and the flow direction of the cleaning water is consistent with that shown in FIG. 2 . The palladium concentration in the wash water produced in wash zone _S1 is about 1.5 mg/l. To adjust the ultrafiltration capacity of the wash water, a 467 g/liter aqueous solution of sodium dimethyldithiocarbamate was added to the wash water. The palladium concentrations in the permeate and concentrate produced by ultrafiltration of the solution are listed in Table 1 (Test 5).

Example 5:

In another trial 6, the same ceramic membrane filter as in Example 1 was used. In this test, the cleaning water obtained according to Example 4 was mixed with the activation bath solution in a volume ratio of 100:1. A 10 g/L aqueous solution of sodium sulfide was added to the mixture. The initial palladium concentration was 8.0 mg/L. The palladium concentrations in the filtrate and concentrate after ultrafiltration are listed in Table 1.

The tests described above produced a concentrate containing a large amount of slurry. After the slurry has settled, the concentrate is distributed to filter presses. The palladium concentration in the palladium-enriched concentrate is between 2 and 5 g/l. The palladium concentration in the filter cake obtained after compression is from 2 to 15% by weight.

Example 6:

In another trial 7, the same ceramic membrane filter as in Example 1 was used. The mixture according to Example 5 was added to the cleaning solution mixture obtained according to Example 2 in a volume ratio of 2:1.

The palladium concentration in the liquid was 4.2 mg/liter. The pH was adjusted to 7 using NaOH solution. Furthermore, 467 g/liter of an aqueous solution of sodium dimethyldithiocarbamate was added to the liquid. The palladium concentrations in the permeate and concentrate obtained after ultrafiltration are listed in Table 1.

It should be understood that the embodiments and implementations described here are for descriptive purposes only, and those skilled in the art can easily conceive of various improvements and changes according to the present application and combinations of features described in the present application, and these are all It is intended to be within the spirit and scope of the invention and covered by the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference.

Table 1: Test No. mixture of products Initial Pd concentration [mg/l] pH Pd concentration in permeate [mg/l] Concentration of Pd in concentrate [mg/l] Add chemicals 1 Cleaning fluid colloidal activator 5.5 5 <0.5 ＞1,000 not added 2 cleaning solution etchant 2.5 3 <0.5 ＞1,000 not added 3 Cleaning liquid colloidal activator + etching solution: 1:1 4.0 7 <0.5 ＞1,000 NaOH 4 Cleaning liquid colloidal activator + etching solution: 1:1 + 1 volume % colloidal activator 15.0 7 <0.5 ＞1,000 NaOH 5 Cleaning fluid ionization activator 1.5 8 <0.5 ＞1,000 Sodium Dimethyl Dithiocarbamate 6 Cleaning liquid ionization activator + 1 volume % ionization activator 8.0 8 <0.5 ＞1,000 Na ₂ S 7 (cleaning liquid ionization activator+1 volume % ionization activator)+cleaning liquid colloidal activator+cleaning liquid etchant: 1:1:1 4.2 7 <0.5 ＞1,000 NaOH, sodium dimethyldithiocarbamate

Claims (20)

1, a kind of method with liquid plating workpiece, described liquid contains at least a precious metal, described method comprises with described liquid and contacts described workpiece, behind the described workpiece of plating, filter described liquid so that from this liquid, isolate described at least a precious metal by at least one ceramic membrane filter device, the evacuation aperture size of wherein said ceramic membrane filter device surpasses 10,000 dalton.

2, method as claimed in claim 1, the evacuation aperture size range of wherein said at least a ceramic membrane filter device are about 15,000 dalton 25,000 dalton extremely.

3, method as claimed in claim 2, the evacuation aperture of wherein said at least one ceramic membrane filter device are of a size of about 20,000 dalton.

4, a method as claimed in any preceding claim, wherein said at least one ceramic membrane filter device is made by aluminum oxide/titanium dioxide/zirconia ceramic material.

5, a method as claimed in any preceding claim, wherein said workpiece are fit to make circuit carrier.

6, a method as claimed in any preceding claim, wherein said precious metal are palladium.

7, method as claimed in claim 6, wherein behind the described workpiece of plating and before filtering described liquid by at least one ceramic membrane filter device, described liquid is mixed with suitable chemical substance changing described at least a precious metal, thereby this precious metal is stayed when filtering basically fully.

8, method as claimed in claim 7, wherein palladium exists with ion and/or ionized form, and described liquid mixes mutually with the chemical substance that is selected from reductive agent, sulphur compound, selenium compound and tellurium compound.

9, method as claimed in claim 8, wherein said chemical substance are selected from hydroborons, amine borine, hypophosphite, inorganic sulphide and organic sulfide.

10, method as claimed in claim 9, wherein palladium exists with colloidal form, and wherein said chemical substance is the pH regulator agent, and it is 3 to 12 that itself and described liquid mixing make the pH scope of solution.

11, the method arbitrary as claim 7-10, it comprises following method steps:

A. described workpiece is contacted with containing the palladium working fluid,

B. then, will attached to the working fluid of described workpiece surface remove with scavenging solution and

C. by described at least one ceramic membrane filter device described working fluid and/or described scavenging solution are filtered, the liquid by described at least one ceramic membrane filter device is penetrating fluid, and the liquid by described at least one ceramic membrane filter device is not concentrated solution.

12, as the method for claim 11, wherein before handling, described working fluid and/or described scavenging solution are mixed with described chemical substance by described at least one ceramic membrane filter device.

13,, wherein the highest scavenging solution that contains the described working fluid of 5 volume % is handled by described at least one ceramic membrane filter device as method arbitrary in claim 11 and 12.

14, as the method for claim 13, wherein in the unit time, described workpiece is contacted with the fresh cleaning solution of predetermined amount, and the amount of the described penetrating fluid that wherein forms in the unit time approximates the amount of the scavenging solution that contacts with described workpiece in the unit time.

15, at least a liquid that contains precious metal of a kind of usefulness comes the equipment of plating workpiece, described equipment comprises the device that described workpiece is contacted with liquid and the device of the described workpiece of clamping, this equipment also comprises the facility of isolating described at least a precious metal from described liquid, this facility comprises at least one ceramic membrane, at least one is delivered to described liquid the pump of described at least one ceramic membrane and the fluid conduits that described liquid is guided to described at least one ceramic membrane by the device that described workpiece is contacted with liquid, the evacuation aperture size of wherein said at least one ceramic membrane surpasses 10,000 dalton.

16, as the device of claim 15, the evacuation aperture size range of wherein said at least one ceramic membrane is that about 15,000 dalton are to about 25,000 dalton.

17, as the device of claim 15 or 16, the evacuation aperture of wherein said at least one ceramic membrane is of a size of about 20,000 dalton.

18, as device arbitrary among the claim 15-17, the facility of wherein isolating described at least a precious metal from described liquid also provides the liquid and chemical substance blended mixing facility that makes from the device that described workpiece is contacted with described liquid.

19, as device arbitrary among the claim 15-18, a heterogeneous separating unit wherein is provided, in this unit, the slurries that produce in the sepn process and isolate the facility of described at least a precious metal in described liquid can carry out sedimentation.

20, as device arbitrary among the claim 15-19, wherein said at least a ceramic membrane is made by aluminum oxide/titanium dioxide/zirconia ceramic material.