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Billions of squeegee strokes into the future
Using real-time verification faulty prints can be automatically identified
When preparing to write a feature, it's amazing how white an empty page or screen can be to a dyslexic like me. It's difficult to believe how liberating the keyboard is. When writing by hand the pen just won't go where the brain wants it to, while reading is sometimes like a slow motion landslide of words. So why the revelations?
The solution is screen printing which has played a key role in the creation of word processors and all things electronic. While many of us were happily creating glorious designs, in vibrant colours, on a host of different substrates, others were taking the screen printing process into areas of engineering excellence that were merely an aspiration for many graphics printers. This area was, and is, electronics production, an increasingly important market for fuel cell, solar cell and other energy creating/saving products.
The UK is fortunate to be the home of many leaders in electronics production, including Gwent Electronic Materials, DEK International, BTP Technical Services and Natgraph. What all these companies deal in is precision. When printing any type of electronic circuit the need is control and repeatability. Screen printing delivers this, allowing the printing of large volumes of devices at relatively high speeds. In this industry, screen printing has become known as a mass imaging technology, compared with digital printing that tends to be used for short run work. It is clear that digital printing technology will increase its application base in this sector. However, for the foreseeable future screen printing will continue as the frontline production tool, while using digital control and stencil imaging technology to streamline the process. This is exemplified by DEK International which produces state-of-the-art printing equipment to serve this global industry's needs.
The two killers of productivity and profitability are machine down time and rejects. DEK addresses these issues with its Intelligent Scaleable Control Area Network (ISCAN) architecture designed to offer control and flexibility via intelligent machine communication. The system initiates actions, monitors their progress and provides feedback to determine the precise conditions that produced a particular lay down of material. The company's Instinctive interface is designed to ease control. The graphics are gaming quality and can access online training and process knowledge. Probably the most powerful tool is HawkEye, and automatic print verification technology that operates at the line beat rate. HawkEye can be configured to assess 100 per cent of printed substrates, providing a go/no-go which means faulty boards can be automatically isolated in real-time.
HawkEye rapidly scans the board as a series of stripes and collects a set of monochrome image data. Comparing these results with the user-defined limits of acceptability, HawkEye quickly indicates whether the board is ready to pass through to component placement or other downstream processing. The user can program HawkEye to inspect only certain areas of the board where, for example, print deposit density may be particularly high. This lets users adjust the total verification cycle time if necessary, thus deriving maximum system value within the line beat rate. All these capabilities are available with DEK's Galaxy, Europa and Horizon printers.
Gwent Electronic Materials, via its various divisions, supplies the solutions/pastes that are printed. Not long ago this comprised just conductive, resistive and insulation (dielectric). Now the product range is increasing as fast as the technologies develop, so much so, that GEM has different divisions to suit various applications and has extended its product range into instruments that enclose the sensing technologies in which their products are the core.
As medical technology develops the opportunity for self and remote diagnosis increases. The most common sensing and measurement regime is glucose levels in blood for diabetics.
It is not just human medicine that is adopting sensor technology. Environmental sensors have been produced to measure pesticide levels in water or other harmful chemicals.
The agri-food industry needs to know sugar levels in fruit and vegetables. In this application GEM produces the instruments as well. Both screen printing and flexographic printing are used in producing the sensors. Flexo tends to be used where very thin deposits are required and screen printing either when heavier deposits are needed or the medium can only be printed using screen. Digital systems are developing but the applications are so numerous there is plenty of room for all processes. The fact screen printing is an ink friendly process means it gives much greater scope for varied chemistries. Substrates used to support the electronic circuitry are polyester, PVC and alumina: a ceramic material.
A typical sensor comprises chemistry, often an enzyme that reacts by changing its electrical characteristic when it comes into contact with the material the system wishes to measure. That enzyme has to be contained and supported, while electrical changes have to be conducted away to a measuring instrument. In essence it is a simple electronic circuit but the chemistries are extremely complex. The circuitry has to be reliable and robust. Screen printing is the ideal production tool for many applications. Eventually nano-technology will replace this form of sensing with molecular level sensors, while quantum computers will govern our lives: but that is billions of squeegee strokes in the future.
It is easy to forget the longstanding application of screen printing in the production of membrane switches. The technology has not substantially changed in recent years but quality and performance has bounded ahead.
Now with the importance of managing MRSA and other infections these surfaces can be antibacterial. RH Technical Industries provides membrane switches, overlays (both plain and backlit with electroluminescence) that use these coatings.
Ultra violet curing systems for conductive inks are now well established, with the cured ink film much more malleable than original brittle tracks. Dielectrics (insulators) are often UV systems but resistive systems especially those used in potentiometers are a long way off.
The boundaries between graphics printing and printed electronics are blurring. This is exemplified by BTP Technical Services which, like DEK, produces quality stencils for the industrial and electronics sector. Through BTP Craftscreen the company was a graphics screen printer for more than 50-years then, eight years ago, it moved into producing precision stencils for the industrial screen printing market. This required a change in thinking from traditional graphic stencil production to working with close tolerances where the characteristics of every stencil were measured and recorded. Individual frames have unique identification numbers enabling traceability throughout their useful life. Although used to working in clean and tidy conditions it was necessary to move into clean room conditions with fully gowned technicians. Temperature and humidity control is essential to ensure accurate measurement and guarantee complete curing of the emulsions.
