Patent Application
20140017410
The present invention provides an electroless plating process, particularly, the present invention provides a continuous process for electroless plating using porous substrate, metal salt solution and reducing solution only to the extent that the membrane is formed;
The present invention further provides a continuous process for electroless plating by using reducing agent separately.
Plating is a surface covering in which a metal is deposited on a surface. Plating has been done for hundreds of years, but is critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, for radiation shielding, and for other purposes. Plating also fins applications in the field of nanotechnology where thin-film deposition has plated objects as small as an atom.
There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate). Other plating techniques include vapor deposition under vacuum and sputter deposition. Recently, plating processes often refer to use of liquids. Metallizing refers to coating metal on non-metallic objects.
Electroless plating, also known as chemical or auto-catalytic plating, is a non-galvanic type of plating method that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent, usually sodium hypophosphite (Note: the hydrogen leaves as a hydride ion), and oxidized thus producing a negative charge on the surface of the part. The most common electroless plating method is electroless nickel plating, although silver, gold and copper layers can also be applied using electroless plating method, as in the technique of Angel gilding.
References may be made to U.S. Pat. No. 6,761,929, which provides for a method for preparation of metal/porous substrate composite membranes by flowing a solution of metal to be plated and the use of the resulting membrane for the production of highly purified hydrogen gas. But the cited U.S. application and other prior arts suffer from several drawbacks including that the metal solution and reducing solution are added together in this process, therefore metal is separated before reaching the membrane/substrate which needs to be plated. The separated metal gets deposited in tubing, pipe lines etc resulting in enormous wastage. This deposited metal cannot be recovered, and can prohibitively add to the cost of plating in case of precious metals. Another disadvantage is that there is no assurance that all parts of substrate are plated. Also there is no assurance of complete filling, so that there are no pinholes, cracks. To overcome the drawbacks of prior art processes, the inventor has developed a novel process of electroless plating.
The main object of the present invention is to provide an electroless plating process.
Another object of the present invention is to provide a process of electroless plating that result in 100% membrane preparation.
Still another object of the present invention is to provide an automatic process for electroless plating that results in 100% membrane preparation.
Yet another object of the present invention is to provide an automatic electroless plating process that prevents any wastage of metal to be plated on the substrate.
Accordingly, present invention provides an electroless plating process for 100% membrane preparation using a porous substrate comprising the steps of:
In another embodiment of the present invention, the plating solution used is selected from metal salt solutions that can produce metal/metal alloy ions and can be reduced by reducing ion like hydrogen to produce metal.
In yet another embodiment of the present invention, the reducing solution used is selected from solution that can produce a reducing ion like hydrogen that can reduce the metal salt solution to metal.
In yet another embodiment of the present invention, the reducing solution used is selected from hydrazine, sodium hypophosphite or formaldehyde.
In yet another embodiment of the present invention, the step of drying the metal deposited substrate comprises heat treating the same at a temperature in the range of 70 to 80° C. followed by annealing at temperature in the range of 350 to 370° C. to obtain plated metal substrate surface.
In yet another embodiment of the present invention, said metal membrane is without any air leakage.
In yet another embodiment of the present invention, a system for performing electroless plating process for plating of a porous substrate with metal wherein said system comprises:
In yet another embodiment of the present invention, the first section and the second section are securable with each other to define the said compartment.
In yet another embodiment of the present invention, the substrate is disposed between the first section and the second section when the said sections are secured with other.
In yet another embodiment of the present invention, the burettes are connected with the inlets using pipes and the burettes are provided with feed control valves.
In yet another embodiment of the present invention, the pressurizing means is selected from a balloon, compressor, gas cylinder.
In yet another embodiment of the present invention, further comprises a heating means heating for any one of the plating or reducing solution.
The present invention provides an electroless plating process wherein 100% plating can be achieved. The present invention provides an automatic process for cleaning, activation and electroless plating for almost 100% plating of substrate surface with substantially no pinholes/cracks of metal on porous substrate comprises:
The plating operation is carried out in three stages:
In the process of the present invention, the substrate is cleaned with water, followed by sensitization and activation of the substrate surface. In the sensitization and activation step, the substrate is treated with SnCl2 solution and then PdCl2 solution.
The porous substrate comprises a first surface and a second surface which is located opposite to the first surface. The first surface of the substrate is contacted with the plating solution containing metal salts and the second surface of the substrate is contacted with a reducing solution. Thereafter a pressure is applied on any one of the said plating and reducing solution so that solution from one side of the substrate permeates through the substrate and reaches the other side causing contact between the plating and reducing solution thereby resulting in deposition of metal on the said other side of the substrate.
For example, when a pressure is applied at the plating solution on the side of the first surface of the substrate, the plating solution permeates through the porous substrate and reaches on to the second surface where it comes in contact with the reducing solution. The contact between the reducing solution and the plating solution which has permeated through the substrate at or near the second surface causes deposition of the metal on the second surface of the substrate. Alternatively, when a pressure is applied at the reducing solution, on the side of the second surface of the substrate, the reducing solution permeates through the porous substrate and reaches on to the first surface where it comes in contact with the plating solution. The contact between the plating solution and the reducing solution which has permeated through the substrate at or near the first surface causes deposition of the metal on the first surface of the substrate.
As it can be clearly noticed, in the process of the present invention the metal is deposited at a surface which is located opposite to the side where pressure is applied. As can be clearly understood, the pressure applied is sufficient so as to result or facilitate permeation of the plating or reducing solution through the porous substrate.
Electroless plating process of the present invention can be used for plating metal on a porous substrate selected from glass, sintered metal and such like preferably ceramic.
In the process of the present invention, the plating solution can be selected from metal salt solutions that can produce metal/metal alloy ions and can be reduced by reducing ion like hydrogen to produce metal. Also, the reducing solution is selected from solution that can produce a reducing ion like hydrogen that can reduce the metal salt solutions to metal. In an aspect of the present invention, the reducing solution is selected from hydrazine, sodium hypophosphite or formaldehyde.
After the metal is deposited on the first or the second surface of the substrate, the substrate is rinsed with water and the metal deposited first or second surface is heat treated to obtain the metal plated substrate surface. In an aspect of the present invention, the heat treatment of the metal deposited first or second surface includes drying the substrate at a temperature in the range of 70 to 80° C. followed by annealing at temperature in the range of 350 to 370° C. to obtain metal plated substrate surface.
In the process of the invention, the porous substrate facilitates the transport of a solution (plating) on one side, when subjected to pressure. The solution (plating) passes to the other side through the porous substrate where it comes in contact with another solution (reducing) on the activated surface and immediately the reduced metal is deposited on the activated surface. The process continues till all the pores are blocked by the reduced metal. As soon as the whole surface area of the activated side of substrate is plated, plating stops automatically. Thereafter, further processing of plated membrane is done by drying, annealing if required, leak free testing and testing of permeability of H2 (if the membrane is permeable to H2 gas). The present invention also provides a system for performing an electroless plating process for plating of a porous substrate with metal.
Referring to
The process described on the above paragraph and equipment can also be used for activation of the substrate. To carry out sensitizing-activation, SnCl2 is subjected to pressure on one side of the cleaned substrate to react with PdCl2 on the other (activating side) or vice versa. Activation will occur on the surface opposite to the pressurized solution.
The following paragraphs describe performing the electroless plating process of the present invention by the system as shown in
All parts (i.e. compartments (1), burettes (12, 12′), pipes etc) of the system (1) are washed with de-ionized water. The bottom section (6) of the compartment (1) is placed over the magnetic heater (9) and the substrate is fixed in the compartment (1). The burettes (12, 12′) are connected to the two sections (2, 3) of the compartment (1). A balloon (11) is fixed on the burette (12) connected to upper section (2) of the compartment (1). The outlet (7) of the lower section (3) was fitted with a thermometer to measure the temperature of the magnetic heater (9). Sensitizing-activating solution, plating solution and reducing solutions are prepared. Activating solution of PdCl2 should be preferably prepared overnight for it to stabilize, while SnCl2 solution should be preferably prepared fresh. Activating solution was put in to burette (12) which is fixed with an air balloon (11), to apply desired pressure. The sensitizing solution is put in the other burette (12′) (i.e. the burette connected with the lower section). After activation of the substrate (4), the solutions were drained out. Burettes containing activating and sensitizing solutions were replaced by those containing plating solution and reducing solution respectively. In other words, burette containing the plating solution in connected with the inlet (5) of the upper section (2) and burette containing the reducing solution is connected with an inlet (6) of the lower section (3). The valve of the burette containing reducing solution is opened and the entire lower section was filled up. The magnetic heater is switched on for heating the reducing solution. As the temperature of the reducing solution reached the required range, the valve of the burette containing the plating solution was opened thereby filling the upper section with the plating solution and the desired pressure is maintained through the balloon. Due to the pressurization, the plating solution permeated through the porous substrate (4) and comes in contact with the reducing solution in the lower section causing deposition or plating of the metal or forming a membrane on the surface of the substrate. After plating, further processing of the synthesized membrane was carried out, such as drying and annealing. The prepared membrane was tested for leaks. Its hydrogen permeability was also tested, as exemplified herein. With reference to example 1, with no air passing through the metal coated substrate, the process of the invention resulting in almost 100% coating with substantially no pinholes or cracks is adequately proven.
As can be understood from the
The membrane formed inside the porous substrate (middle of the substrate) is called a composite membrane consisting of metal and substrate itself. It acts as a membrane. This is different from the pure metal membrane formed on the “surface” of the substrate. The basic differences are, the membrane formed on the surface is almost a pure metal membrane & can be separated from the substrate & may have additional advantages like its thickness is very small. But the membrane formed inside the substrate is a composite of metal & the substrate itself. Although it may function as a membrane, its thickness may be huge and it may not be separable from the substrate.
Both types of membranes can be prepared by the system and process of the present invention.
Substrate used: Ceramic disk
Copper plating bath composition:
Steps for Cu membrane preparation using electroless plating:
Step 1: Cleaning of Support/Substrate
Step 2: Activation of Support/Substrate (One Side Only)
Observations
The support becomes reddish brown in colour.
Step: 3 Copper Electroless Plating
This confirmed that the substrate was coated almost 100% with the metal.
Components used for Pd electroless plating are reported in table given below. Electroless plating solutions are widely reported in literature. In the present invention, same plating solution is used but use the reducing agent from this solution for plating has done separately.
Substrate used: Sintered SS plate (Sintered stainless steel plate)
Plating solution composition:
Table 2 was used for Pd membrane preparation (similar to the copper membrane). Procedure was same. The electroless plating solution was replaced by the Pd electroless plating solution of table 2.
Components used for Pd electroless plating are reported in table given below.
Substrate used: Ceramic disk
Plating solution composition:
Table 3 was used for Pd—Ag membrane preparation (similar to the copper membrane). Procedure was same. The electroless plating solution was replaced by the Pd—Ag electroless plating solution of table 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3101/DEL/2010 | Dec 2010 | IN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2011/055963 | 12/27/2011 | WO | 00 | 9/13/2013 |
