Wikipedia defines ink as a liquid containing various pigments and/or dyes used for coloring a surface to produce an image, text or design. Ink is used for drawing and/or writing with a pen, brush or quill. Thicker inks, in paste form, are used extensively in letterpress and lithographic printing.
Ink is a complex medium composed of solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, fluorescers and other materials.
Wikipedia defines a coating as a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wet ability, corrosion resistance, wear resistance and scratch resistance. In other cases, in particular in printing processes and semiconductor device fabrication where the substrate is a wafer, the coating forms an essential part of the finished product.
Coating and printing processes involve the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil or sheet stock. A roll of substrate, when wound through the coating machine, is typically called a web.
Coatings may be applied as liquids, gases or solids. Coatings can be measured and tested for proper opacity and film thickness by using a drawdown card.
Conductive ink is an ink that conducts electricity, these materials may be classed as fired high solids systems or polymer thick film (PTF) systems that allow circuits to be drawn or printed on a variety of substrate materials such as polyester to paper. These types of materials usually contain conductive materials such as powdered or flaked silver and carbon like materials.
Conductive inks can be a more economical way to lay down a modern conductive trace when compared to traditional industrial standards such as etching copper from copper plated substrates to form the same conductive traces on relevant substrates, as printing is a purely additive process producing little to no waste steams which then have to be recovered or treated. Silver inks have multiple uses today, including printing RFID tags as used in modern transit tickets, and they can be used to improvise or repair circuits on printed circuit boards. Computer keyboards contain membranes with printed circuits that sense when a key is pressed. Windshield defrosters consisting of resistive traces applied to the glass are also printed.
Printed paper and plastic sheets have problematic characteristics, primarily high resistance and lack of rigidity. The resistances are too high for the majority of circuit board work, and the non-rigid nature of the materials permits undesirable forces to be exerted on component connections, causing reliability problems. Consequently such materials are only used in a restricted range of applications, usually where the flexibility is important and no parts are mounted on the sheet.
Electromagnetic interference (EMI) and the narrower category of radio frequency interference (RFI) have been a persistent problem in the electronics industry since the earliest days. The traditional example is the “snow” seen on analog television displays; audible static on telephones and radios is another. Such interference can also harm the operation of computers, cell phones, networks and other electronics.
The challenges and opportunities have grown as the kinds of systems that are impacted by EMI/RFI have multiplied. Luckily for device manufacturers, and for the suppliers of electromagnetic compatibility (EMC) products, EMI can be shielded to prevent this performance degradation. Shielding is often as simple as surrounding sensitive components, or troublesome emitters, within a conductive box or other enclosure. The types of enclosures used include small boxes to cover parts of circuit boards, conductive dips for individual components, jacketing or conduits for wires and cabling, and the cases or outer “skins” of devices or appliances.
EMC markets are created by two separate but related objectives:
• Keeping external interference out; and
• Keeping internal signals in, which could cause interference in other devices.
Practically all electronic devices are subject to EMC regulations and hence must demonstrate, and be built for, a minimal level of electromagnetic leakage as well as a tolerance for EMI that may come from other sources. And as appliances become “smarter” in conjunction with the smart-grid rollouts, they will also become both more sensitive to and more likely to produce EMI.
The materials, products and strategies used for EMC are fairly similar to those used for ESD protection to an extent. Both involve providing a measure of conductivity to the outer surface of sensitive devices or equipment, but they require different levels of conductivity. For ESD protection, charges are carried to ground and/or resistively dissipated, and can accommodate, or even require, low levels of surface conductivity. On the other hand, EMI shielding requires high mobility of the electrons in the material, meaning much higher conductivity.
These conditions have implications for the materials used. For coatings or filled plastics, generally a much larger quantity of conductive material must be used for EMC, raising costs. And some marginally conductive materials used as fillers for ESD materials may be too resistive even in bulk to be used for EMC materials. Higher conductivity requirements also open some new opportunities. Some filler materials can now be used more comfortably within their percolation thresholds, for instance, and metal foils and sheets become reasonable material options.
According to NanoMarkets, there are several trends occurring that are leading to important new opportunities emerging in the EMC industry.
The explosion in the number of wireless phones in recent years has produced billions of new ever-present devices that need to be protected. Well over one billion cell phones are sold every year and it is not just because the phones themselves emit and receive RF signals for communication; the large number of components within the phones also emits EMI and can be sensitive to it.
The shrinking size of electronic devices and the components within them is making EMC more problematic. The smaller size of the components and their closer proximity to one another makes them more sensitive to the EMI from their neighbors within the same device. In addition, the smaller size of the overall device reduces the space available for EMI shielding solutions. Simple off-the-shelf shielding boxes that worked well in the past often cannot do the job today because they simply will not fit.
Lastly, higher radio frequencies are also becoming more common for communications and this produces problems on two levels. For one, the potential victims of these higher frequencies need to be protected by shielding that is capable of dampening such high frequencies. Also, the equipment that sends and receives these frequencies must be able to block the lower frequencies while receiving the intended band.
Tune in next month when we will continue our discussion of these trends and explore the emerging application area of electronic paper.
Where do inks & coatings intersect?
Published June 1, 2010
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