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Abstract— This report briefly summaries the amount of

activities carried out to achieve high conductivity of the silver ink on resin-coated paper substrate. The report turns around with discussing the obvious choice of silver nanoparticles as ink for flexible electronics. Then further it goes on to discussing the apparatus set-up for printing, pre-heating the equipment-oven sintering requirements for silver ink and additively depositing ink on paper substrate for variable amount of time. At each interval the measurements were noted down by changing the factors, which are important and five conclusions are made to summaries this report.

Index Terms – silver nanoparticles, industrial oven, cleaning and clogging awareness, conclusion

I. INTRODUCTION Out of all the printable materials available today we found

that Metal nanoparticles possess the highest conductivity in the printable region. To this end, review of papers suggest that silver is the obvious choice due to its high yield, ability to withstand the charge for the longer duration and it’s printability using on-the-shelf desktop printer.

The selection of substrate for printing was the second crucial thing we needed to figure out as review of papers tell that silver ink requires sintering at 150 Deg. C. Obviously, the normal printing paper would not suffice this condition and thus, we started looking for specialized paper for printing.

II. GUIDELINES FOR SELECTION OF SUPPLIERS From the aforementioned criteria we sent out our

requirements at various companies located inside and outside of the United States. To list a few, they were Nanomass Technologies, Binghamton, and Advanced nanoparticles, California and AGIC: Electronics Everywhere located in Korea. Reaching out these suppliers and placing order for the correct material consumed approximately 20 days of time and then delivery took another week.

After initial sorting we found that AGIC has already proven results of their ink as conductive on resin coated paper. So, we ordered 50ml of NBSIJ-FD02 from Mitsubishi Imaging Supplier, which costs us $200 for a bottle and also a bundle of resin coated papers, which has ability to sustain high temperature. In addition to this, the paper has very high

dielectric constant and very low loss tangent, which are prime condition for electric circuits to work on the paper substrate.

Detailed ink properties from the supplier catalogue such as Ag content, viscosity of the ink, Density, cleanup criteria, print width & thickness, color, adhesion and resistance properties can be found at (https://www.dropbox.com/home/BrandonChi/Reference%20Papers/Hardik?preview=Silver+Nano+Ink+SPEC+SHEET-Nano-V4.pdf). Please visit our drop box folder to have a quick look at these properties as they are of our particular interest and affect the print quality.

III. GUIDELINES FOR SETTING UP THE APPARTUS As print quality is greatly affected by the types of printer

and printing environment, throughout the experimental process we took care of this aspect carefully. It begins first by cleaning all the cartridges and nozzles prior to use, which takes considerable time. Clean the cartridges with the highly volatile ethanol and then, with DI water to confirm that there is no dust particle left into it. Any dust particle left into the passage will cause the nozzle to clog may be while printing is going on or when it’s settle down. In either case it affects the print quality and results in time waste in cleaning. Second, carefully suck the silver ink from the bottle from the syringe provided by the supplier and attach filter in its way before it enters the cartridge. This way external dust particles can be restricted from going into the printing nozzle.

While one is setting up the apparatus for ideal printing process, it is good practice to start the oven at the same time and preheat it upto the 100 Deg C. Preheating is one of the interesting things we found while carrying out the process, which in my view has no one adopted. (No paper has cited about the preheating and its results; researchers are heating the print for sintering but still preheat gives cutting edge quality). How and why preheating is essential here will be discussed later in this report when we reach there. We’ve identified the troubles related to the cleaning and have decided to use single nozzle print head for relatively much faster operations. Currently, Dr. Zhou is leading this direction for arranging this new set-up and by the time, once we are finalize with which Antenna design to use, we will have new print head available.

Preparation for Printing Flexible Electronics Circuits using Desktop Inkjet Printer

Hardik U. Gandhi, MS Candidate, State University of New York at Buffalo

Dr. Chi Zhou, Assistant Professor, State University of New York at Buffalo

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IV. EXPERIMENTS WITH SILVER NANOPARTICLES INK Once the silver ink reached to laboratory we thoroughly

followed aforementioned guidelines and printed the ink on the regular paper to check whether our Epson workforce 30 printer is apt to print silver or not. We successfully printed shapes like U, M and also a Straight-line, meaning that printer is capable of printing the silver ink we got from the surprise. It’s left us in no surprise that the color didn’t turn into the golden as we had used regular paper.

Then, in the next trial we print the same drawings on the special resin-coated paper, but this time it left us in surprise because we observed series of gaps within the design, and this led us to conclude that at some moment ink was not coming out from the nozzle and we have to clean the apparatus before every operation. Second issue we observed was, there was infinite resistivity although we followed every instructions from the suppliers manual. So, we decided to sinter the print using hot-gun readily available in the laboratory.

During, the next several iterations we sketch a line on the resin-coated paper by hand and immediately sintered it using hot-gun but still we observed not a slight amount of conductivity, which put us in amusement. To this end, I again reviewed all the research papers and found that sintering plays a significant role and nanoparticles have to be fused with each other to be considered as continuous ink to obtain the desired conductivity. And, I highly recommend skimming the chapter written by on of the Ph.D students at Georgia Institute of Technology. Here is the link for this chapter to our Dropbox. (https://www.dropbox.com/home/BrandonChi/Reference%20Papers/Hardik?preview=how+to+get+conductivity+of+silver+ink.pdf)

Here they are using industrial oven for sintering of FS Series by Test Equity, which costs around $2500. But, we decided to use the oven available in our laboratory to first check the conductivity although it’s more that a decade old. Figure below further summarizes this practice.

Figure 1 Effect of sintering time and conductivity of the ink

Figure 1 shows the iterative process of sintering the ink for different duration of time. Here, we observed three important features of the silver ink. First, the more the time the ink is sintered at same temperature the better is the conductivity. Second, For the same sintering time if we keeps on increasing the temperature, but below the upper critical limit that is 150 Deg. C, better the resultant conductivity is. By careful observation we found that our substrate was already preheated because of earlier processes and when we again sketch a line and sintered it for same temperature for same amount of time we obtain much better conductivity, meaning that preheating of substrates causes the incoming drops of silver ink to be arranged in same directions and fused easily with each other and thus, resulting in much better conductivity when compared to previous treatment. Theses are the three main observations we made during this process.

Looking at the figure it is evident that some of the regions are golden in color, which has very high conductivity when compared to the other regions in the sketch, meaning that silver ink when sintered properly resembles golden patch. But still advantage of adding material layer by layer is still missing here which is discussed in next topic.

V. SILVER NANOPARTICLES INK WHEN DEPOSITED ADDITIVELY The aim of this whole exercise was to take advantage of

additively depositing the silver ink layer-by-layer to obtain the best conductivity. We randomized the whole experiment and printed as many as 10 layers additively and sintered the whole print for 1hr for constant 120 Deg. C.

Figure 2 Additively printed line using Epson workforce 30 and

silver nanoparticles ink

From the above figure we’ve drawn one important conclusion, which is when silver nanoparticles ink deposited additively on the resin-coated paper substrate gives us better conductivity compared to previous results. Table 1 provides the summary of result of this process.

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Table 1. Comparisons of Number of additively printed layers and resistivity

Sr No No of Prints Resistivity

1 3 Infinity

2 5 42.6 K. Ohms

3 10 283.3 Ohms

4 8 368 Ohms

5 1 Infinity

6 7 1.36 K. Ohms

7 6 7.85 K. Ohms

8 9 264 Ohms

9 4 Infinity

10 2 Infinity

Kindly note that results are measured in terms of resistivity and concluded in terms of conductivity. The next thing now was to analyze the conductivity of silver ink for different length. For this purpose, we chose the design shown below:

Figure 3 Test of conductivity for different length

In this, experiment we printed five layers of ‘A’ using Epson Workforce 30 print head and measured the conductivity of print for different size of length. We noticed that conductivity is not highly proportional and influenced by the length, meaning that if we provide proper combinations for printing we can get the same conductivity for infinite length theoretically that we observed for smaller lengths.

VI. CONCLUSIONS I’ve periodically drawn various conclusions throughout the

entire exercise but here I would like to provide general summary, which gives reader quick insight about this report.

1. For the same temperature setting conductivity of silver

ink depends upon amount of time it has been sintered 2. For the same sintering time the measure of

conductivity depends upon amount of time it’s been sintered

3. Preheat of substrate has significant effect upon the conductivity of the ink

4. When the silver ink deposited layer-by-layer and sintered for same amount of time it gives much higher conductivity

5. For carefully performed experiment theoretically we can obtain same conductivity, meaning resistance within the fused silver ink can be considered negligible

VII. SCOPE OF IMPROVEMENT We still believe that we are in the very early stage of this

experiment and there is a tremendous scope of improvement in this process. I would like to mention couple of quick important points we have in our mind and we are motivated to introduce them while printing actual Antenna Design.

First being, instead of highly complicated inkjet printer we are going to use single nozzle print head and substrate laying on the heated plate, which confirms the grains are oriented in the same directions to still get higher conductivity. Second being, we still believe that if we sinter the ink into the vacuum oven we can still nullify the probable oxidization of silver ink, which can further improves the current state of conductivity.