PCB News - Researchers invent printable circuit board inkjet printer

After the birth of conductive ink, ordinary inkjet printers can also complete the production of flexible circuit boards within a few minutes, which doubles the development speed and cost of flexible wearable devices.

In this era when almost every family has a tablet computer, what is the use of buying an inkjet printer? Printing work documents, helping children prepare materials, and occasionally typing two photos, may end up in dust. Or, according to the ideas of several university researchers, it can also become an important part of personalized production.

Many researchers from the Georgia Institute of Technology, the University of Tokyo, and Microsoft (37.4, 0.32, 0.86%) Research Institute recently found a technology for rapid development of electronic equipment, which can directly produce circuit boards through home inkjet printers.

With a low-cost 3D printer and a shell made by laser cutting technology, this technology is expected to further reduce the R&D threshold for hardware entrepreneurship, help entrepreneurs quickly implement ideas, improve designs, and ultimately bring innovative smart toys or wearable devices.

When you disassemble a computer or mobile phone, you will see one or more PCB circuit boards. PCB circuit boards are generally green, but they are often processed into red, blue, black, or any other color the designer wants. Regardless of the power supply of the processor, or the signal transmission between the components, it is completed through the metal wires printed on these small boards. They are often mass-produced by professional equipment in huge workshops.

Before mass production starts, developers need to make several circuit boards to test the design, and then modify the design based on the test results. This process is called proofing or prototyping.

Breadboard proofing is often used in the initial stage of university experiment courses and product development. The user inserts components such as wires, sensors, resistors, etc. on a whiteboard with dense interfaces to simulate the performance of the final electronic product. It is very convenient to change the design on the breadboard, but its size is huge, and the reliability and performance are not in line with the finished product. Sooner or later, developers still have to proof on the PCB printed circuit board.

In order to help entrepreneurs and researchers quickly produce circuit boards, some companies provide online design submission and express delivery to users after production is completed. However, it takes at least one day for such a production mode to get the PCB circuit board, which seriously slows down the product development speed, and it takes a week to change the design twice.

As the cost of 3D printers and laser cutting machines drops, hardware entrepreneurs have been able to try out many different housing designs in a day. The long processing cycle of PCB circuit boards has become a shortcoming at the beginning of entrepreneurial hardware product design.

"We think we should bring a way to quickly proof and customize PCB boards," said Gregory Abowd, a professor in the School of Interactive Computers at Georgia Institute of Technology, who believes that this technology should be faster and cheaper. People who want to practice can afford it."

The latest breakthroughs in materials science made Abode's idea possible. Mitsubishi researcher Wu Xuanfangshu has invented a conductive ink that does not require high-temperature treatment and undergoes a chemical reaction to produce conductivity after drying. It dissolves silver nanoparticles with a diameter of less than 0.1 microns in a special solvent containing polymer latex, and the ink will become conductive within a few seconds after drying.

In order to ensure that the conductive ink can be ejected smoothly from the nozzle of the printer, Mitsubishi has optimized the ink viscosity, surface tension, volatility and particle size. The mass-produced version is priced at 20,000 yen per 100 ml. When used as a printed circuit board, a 1mm wide circuit averages 5 cents per meter, and the cost is not high.

Researchers have tested this conductive ink on a variety of home inkjet printers and found that inkjet printers with larger ink output can be used normally, and the cheapest one is less than $100. The researcher used a needle tube to inject conductive ink into a clean, empty ink cartridge. In order to prevent floating objects from mixing into the ink to affect the conductivity, a disposable filter tube is required during the injection process.

Conductive ink requires the paper to have low electrical resistance, and at the same time, it is necessary to prevent the ink from spreading to ensure conductivity. Surface treatment is necessary. Experiments have found that glossy photo printing paper and transparent PET plastic film can meet the needs of circuit printing. These materials are soft and bendable, suitable for the development of flexible wearable electronic devices. This is something that general PCB board customization services cannot provide.

The circuit printing itself does not require special software. The developer can use it only by converting the designed circuit diagram into a dot matrix picture. But the printed circuit should not be too thin, too thin to ensure conductivity. Therefore, the photo mode must be selected when printing. At this time, the printer will mix the conductor ink in the three areas of cyan, red, and yellow to form black, and the ink output is higher than that of the text mode using only the black ink cartridge.

Researchers found that the resistance of inkjet printed circuit boards will change over time and will increase by 15% after 7 months. This is the result of the oxidation of silver nanoparticles, which will affect the long-term use of the circuit board. The solution is also very simple, directly using a household photo laminator to press a layer of film on the circuit board can effectively prevent oxidation.

The circuit board is just the basics. The next step after printing is to install components such as processors, resistors, and sensors. The components of the traditional PCB board are all fixed by welding, which is very firm. But soldering requires a high temperature of at least 180°C, which will damage the paper at the bottom of the circuit board and affect the solidified circuit.

The solution found by the researchers is to stick the components with conductive silver glue, which is the strongest installation method. In an oven at 65°C, the conductive silver glue can fix the components within ten minutes. In addition, the conductive double-sided adhesive produced by 3M can also be used to fix components.

In addition to the PCB circuit board itself, developers can also directly ink-jet print simple antennas and even touch sensors. For example, add touch buttons to children's toys, and play music after feeling the touch. The cost of printing such antennas and sensors is often only tens of cents.

The production of electronic circuit boards is a huge market, with an output value of US$9.4 billion last year. Xerox Laboratories (PARC) has also made a similar attempt. This year it launched a conductive ink called Silver Bullet, which can print circuits directly on plastic sheets. The printed plastic circuit board needs to be heated at a high temperature of 150°C for several hours before components can be installed. In addition, Xerox's new materials require the use of industrial-grade printers from companies such as Fujitsu, and the cost is usually more than US$50,000.

Compared to Xerox’s dedicated inkjet printing equipment, the Georgia Institute of Technology’s solution is only $300, and the printing speed is also faster.

In 1988, Mark Weiser, the chief scientist of Xerox Laboratories, put forward the concept of pervasive computing-the birth of a large number of wearable devices, tablet devices and large-screen interactive devices will bring computers into everything around users. Wei Ze's prediction has gradually become a reality.

Assistant Professor Hiroshi Kawahara of the University of Tokyo who participated in the project believes that his research is an important step towards pervasive computing. At this year's Ubiquitous Computing Conference, Hiroshi Kawahara published a paper detailing the details and prospects of instant inkjet printing circuit technology. He wrote in the paper: "All the materials used in the research are directly available on the market. You can experiment directly at home. This method can print PCB circuit boards, sensors and antennas at a very low cost., Brings many new opportunities."