Patent Application
20050274933
The present invention relates to printed circuits or devices in the electronics industry, and in particular, to a formulation for printing organometallic compounds for use in forming conductive traces on substrates.
Laser-assisted selective deposition of conductive metals is an attractive approach to the customization needs of the electronics industry. For more than about 20 years much effort has been undertaken in attempting to produce acceptable individual metal features in electronic components or circuits by a direct laser writing process. Normally, a device is prepared for subsequent direct laser writing by a spin-coating process which applies a uniform film over a surface.
Spin-coating is a known process used for applying a thin film, such as a metal, to a substrate in the manufacture of circuits. A typical spin-coating process involves depositing a small puddle of a fluid resin onto the center of the substrate and then spinning the substrate at high speed. However, spin-coating processes generally involve a relatively high cost of materials and a further washing process to remove unwanted material.
Another disadvantage of circuit manufacture by direct laser writing is that the width of a deposited metal trace is limited by thermal effects in the laser beam. Presently, even if a laser beam is focused to a diameter of about 20 μm the achievable minimum trace width is about 40 μm.
Another known circuit manufacture process involves etching. A number of variations of etching methods are known, such as wet etching (whereby material is dissolved when immersed in a chemical solution), and dry etching (whereby material is sputtered or dissolved using reactive ions or a vapor phase etchant). However, these methods have significant disadvantages such as a requirement to use a mask of the desired circuit layout pattern that can withstand the etching process. Generally, etching processes and use of masks are considered relatively expensive and require longer turn around times in the manufacture of circuitry.
U.S. Pat. No. 4,574,095 discloses deposition of copper on a substrate by a process in which small palladium clusters or seeds are first deposited on a substrate. Selective deposition of the palladium seeds is accomplished by contacting the substrate with the vapor of a palladium compound and selectively irradiating the complex with light, which can be a laser. The substrate is first covered with photoresist or polymer and selectively irradiated, through a mask, with a pulsed excimer laser. Removal of the polymer occurs in the irradiated area. The film then acts as a seed for plating of copper. This method requires use of a photoresist and a mask and is a direct laser writing process having the associated disadvantages.
U.S. Pat. No. 4,853,252 discloses transfer of a printed pattern in the manufacture of printed circuit boards. A grainy carrier substance of a coating agent affords a good adhesive foundation in a substrate which is controllable through the use of energy radiation. The coating agent is applied to the surface of the substrate S. A laser is utilized as an energy beam. The focussing of the laser beam L is adjustable, whereby the diameter of the laser beam L at the substrate surface can be set to diameters of between approximately 50 microns to about 400 microns. The coating agent includes individual particles of metal M. The laser beam L is guided over the surface of the substrate S and creates a superficial melting of the substrate. This method requires the conductor pattern to be constructed by chemical metal deposition or by chemical and subsequent galvanic metal deposition and relies on a laser heating process to adhere the coating agent to the substrate.
Accordingly, there is need for a printing system which overcomes or at least ameliorates the above-described problems. The present invention addresses this need.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.
According to one broad form of the present invention, there is provided a formulation able to be printed onto a substrate for use in forming a desired conductive trace layout on the substrate, the formulation including at least one organometallic compound dissolved in at least one organic solvent, whereby metal from the organometallic compound is deposited on the substrate when the organometallic compound is heated.
This and other objects or advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the embodiments as illustrated in the drawing figures.
The present invention should become apparent from the following description, which is given by way of example only, of a preferred but non-limiting embodiment thereof, described in connection with the accompanying figures.
Before proceeding with the detailed description, it will be appreciated by those skilled in the art of the present invention that the foregoing description of the preferred embodiments of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms described. Many modifications and variations may be made to the embodiments shown in the Figures without departing from the spirit and scope of the invention.
In a first broad form of the present invention, there is provided a formulation able to be printed onto a substrate for use in forming a desired conductive trace layout on the substrate, the formulation including at least one organometallic compound dissolved in at least one organic solvent, whereby metal from the organometallic compound is deposited on the substrate when the organometallic compound is heated. In an embodiment, the at least one organic solvent is water-miscible and the organometallic compound is water soluble. The organometallic compound is in the form of at least one of an acetate, carboxylate or amine complex. Furthermore, the organometallic compound contains at least one of silver, gold, aluminium, copper or palladium. Additionally, the organometallic compound can include an organic solvent wherein the organic solvent is at least one of a ketone, pentandiol or triol.
In another embodiment, there is provided a chemical solution able to be printed onto a substrate using an inkjet printer and for use in forming a desired metallic trace layout on the substrate, the chemical solution including at least one organometallic compound dissolved in at least one water-miscible organic solvent, whereby metal from the organometallic compound is deposited on the substrate as a result of heating of the substrate by laser light absorbed near or at an interface between the printed chemical solution and the substrate.
In a third embodiment, there is provided a formulation able to be printed onto a substrate for use in forming a desired conductive trace layout on the substrate. The formulation includes an organometallic compound being less than 50% of the formulation by weight, at least one organic solvent being less than 50% of the formulation by weight and water being more than 50% of the formulation by weight whereby metal from the organometallic compound is deposited on the substrate when the organometallic compound is heated.
In another aspect, inkjet technology is utilised as a microprinting tool. An inkjet printer is used to print organometallic compounds on substrates, such as, but not limited to, glass, polyimide, ceramic, paper, etc. According to this aspect of the invention, a relatively narrow conductive trace width can be achieved, for example, less than or equal to 20 μm. Additionally, the width of the conductive trace is independent from the diameter of a laser beam used to effect deposition of the conductive material, for example, a metal such as copper. By removing the requirement of a mask or a washing process the cost of manufacture of a circuit is significantly reduced. Consequently, the complete circuit manufacture process is simplified and is a cheaper and more convenient dry process.
Furthermore, the total turn around time for the manufacture of a circuit is reduced and the reliability of circuits manufactured by such a dry process is improved. Additionally, a relatively fine or narrow conductive trace width can be achieved without reliance on masks and etching processes.
According to yet another aspect, by precisely controlling the height of deposited conductive material, the remaining thin film of the organometallic compound can be used as a protective layer to prevent the deposited conductive trace layer from oxidising due to contact with the ambient atmosphere.
Environmental advantages are also realized such as a reduction in the amount or type of various chemicals required to be deposed of, and a reduction in the volume of water required during the manufacturing process.
Furthermore, the deposited conductive trace layouts can be used to perform the function of a wide variety of circuits. For example, a radio-frequency identification (RF ID) coil can be manufactured and deposited on a variety of substrates. This leads to a reduction in the cost of manufacturing RF ID coils, as well as an increase in the flexibility to accelerate the design cycle time.
In an embodiment, the organometallic compound is water soluble and includes a metal such as, silver (Ag), gold (Au), aluminium (Al), copper (Cu), or palladium (Pd). The formulation to dissolve the organometallic compound is a mixture of water-miscible organic solvents.
The following examples provide a more detailed discussion of various embodiments of the present invention. The examples are intended to be merely illustrative and not limiting to the scope of the present invention.
Illustrated in
The laser light beam 14 or the substrate 24 are then moved so that the laser light beam 14 irradiates other interface areas (not illustrated) resulting in deposition of other layers of conductive traces (also shown as layers 28) on the substrate 24 near or at the other interface areas as they are heated. The laser light beam 14 may be scanned over the desired conductive trace layout in any manner that achieves heating of the substrate 24 in all of the desired interface areas between the printed organometallic compound 22 and the substrate 24.
In an embodiment, the organometallic compound is substantially transparent to the laser light so that the laser light beam 14 is substantially transmitted by the printed organometallic compound 22 and is substantially absorbed by the substrate material 24. Different organometallic compounds may react better with different laser light sources 12 producing different wavelengths of laser light.
According to one particular aspect, relative movement of the laser light beam 14 and the substrate 24 can be achieved by moving the laser light beam 14 using a galvanometer 16 and/or moving the substrate 24 using a x-y stage 18. The laser light beam 14 is manipulated by optical components illustrated in
It should be noted that although reference to laser light 14 is made, it is possible that other forms of electromagnetic radiation could be utilised to effectively heat the interface area 26 of the substrate 24. All that is desired is that the electromagnetic radiation can pass through the organometallic compound 22 and release energy in the substrate material 24 to heat the interface region 26.
It should also be noted that it is not essential that organometallic compound layer 22 remains after heating. It is possible, for heating of the organometallic compound to result in complete deposition of available conductive material 28. Hence, no organometallic compound layer 22 would remain overlaying the conductive trace layer 28 after heating.
In
The following discussion should not be construed as limiting to the scope of the present invention. Referring back to
Cu(HCOO)2.2H2O→Cu(HCOO)2+2H2O i.
Cu(HCOO)2→Cu+H2+2CO2 ii.
The resulting hydrogen (H2) and carbon dioxide (CO2) can be absorbed by an exhaust system to capture these by-product gases. The metallic trace is deposited copper (Cu). In one form, the printer is a thermal inkjet printer, for example the Hewlett-Packard deskjet printer. Other types of inkjet printers may be used, for example a piezo inkjet printer.
It is possible that the thickness of the conductive trace 28 may not satisfy the conductivity requirement for certain electronic products. As such, it is possible to use electroless plating as an additional step in order to build up a thicker conductive trace layer 28. For example, the conductive trace layer can be built up to a height of about 1 to 3 μm.
An electroless plating step may utilise the same type of metal deposited from the organometallic compound or a different type of metal, for example combinations such as copper and copper, copper and gold, copper and palladium, etc, are possible. Any circuit that can be printed on a particular substrate can be produced according to the above-described embodiments.
If the quantity or height of deposited conductive trace 28 is precisely controlled by the level of heating at the interface 26, then a thin layer of organometallic compound 22 can be allowed to remain and overlay the deposited metal 28. This can be desirable as the remaining organometallic compound film 22 can provide a protective layer to prevent the underlying conductive layer 28 from oxidising in ambient air.
According to another aspect, a radio-frequency identification (RF ID) coil can be manufactured according to the present invention. The current process to produce a RF ID coil in the prior art includes chemical etching and CNC milling. This prior art technique includes significant problems, for example: higher costs due to waste of copper material, higher costs due to disposing of the chemical acid solution, higher costs due to specialised equipment requirements, environmental disadvantages that may result from the improper disposing of waste materials such as copper and contaminated water, and a longer design cycle time due to the requirement to design masks.
By using a normal inkjet printer with a suitable organometallic compound, such as a copper formate, once the RF ID coil design has been prepared, the design can be promptly printed onto any desired and suitable substrate. A Nd:YAG laser with a wavelength of 532 nanometres can be used to decompose the copper formate so as to form a copper trace layout that is the same as the designed RF ID coil printed on the substrate. A wide variety of substrates can be used such as glass, plastics, ceramics, paper, etc. Such a process leads to significant cost savings, is more environmental friendly, and allows faster design times and circuit prototyping.
According to yet another embodiment, an organometallic compound that can be utilised as part of an inkjet formulation that can be introduced into a printer cartridge. In order to achieve proper drop ejection of the solution (i.e. formulation) from printer nozzles, physical properties of the solution should be optimized, such as the surface tension and viscosity of the solution. Quality drops from nozzles translate into quality conductive traces.
In order to achieve a higher density of organometallic compound on a substrate after each print, higher concentration of organometallic compound is desired. However, this can pose a challenge when considering solubility of the organometallic compound in solution when printing. The higher the concentration of the organometallic compound, the higher the tendency that burnt residues may be left over on the heater surface after printing. The presence of residue will degrade the quality and stability of subsequent drops. Hence, the type of solvents and their concentrations need to be optimized.
The formulation contains at least one water soluble organometallic compound. The organometallic compound can be in the form of an acetate, carboxylate or an amine complex. The metal component of the organometallic compound can include silver (Ag), gold (Au), aluminium (Al), copper (Cu), and/or palladium (Pd). The vehicle to dissolve the organometallic compound may include at least one water-miscible organic solvent such as nitrogen-containing ketones (e.g. 2-pyrrolidone, N-methyl-pyrrolid-2-one (NMP)), pentandiols (e.g. 1,2-pentandiol, 1,5-pentandiol) and/or triols (e.g. glycerol).
A specific example provided below in Table 1 however, numerous other organometallic compounds and inkjet formulations are possible.
It should be noted with reference to Table 1 that DBOS (“Drop Break-off Observation System”) is a tool used to observe drops fired from inkjet cartridge nozzles. A DBOS image 50 shows a snapshot of the moment drops are ejected from the nozzles, as illustrated in
It is demonstrated that the inkjet formulation presented in Table 1 can be printed by a thermal inkjet printer with acceptable quality. Thus, following the aforementioned laser-induced decomposition process a conductive copper trace 72 was deposited on a substrate after printing of a formulation containing an organometallic compound by thermal ink jet printing.
Hence, there has been provided a formulation for printing organometallic compounds for use in forming conductive traces on substrates. Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.
