Have you ever noticed how hard it is to make some things go away? Not that I’m complaining here, but I just heard someone a few weeks ago, compare screenprinting to cockroaches. I was pretty sure I knew where they were going with the comment but I wanted to hear their take on it. It went along the lines of there is always a new breed or variation that shows up just before you think the one you were working with has died out. This comment is especially true with regard to industrial and printed electronic screen printing.

Expanding on that odd thought process, I personally tend to think of it from another direction. Like the cockroach, screen printing is hard to exterminate because the chemistry is constantly changing. Yes, I realize that it’s a genetic issue with our six-legged buddies, but with screen printing, especially industrial screen printing, the chemistry of the inks and substrates we use are the genetics of the breed. It’s what we can put through mesh that keeps the process constantly evolving and viable. Just realizing what industrial and printed electronic products are screen printed can give you an idea of the scale of the industry.

One of the most obvious (and not so new) areas of ink chemistry is the conductive inks. These have been around for a while, even longer for that matter than rear window defroster grids on automobiles which are about the limit of the average person’s knowledge of conductive ink. Think about that one for a minute and then we’ll look at the rest of the car before we get out and move into the house.

Every car has a rear window defroster grid now but the first ones appeared only in the late 1950’s. They were and still primarily are, screen printed lines of metallic compounds that are fused together with heat while the windshield is being shaped on a mold. When it’s complete, they conduct electricity and generate heat. Some are also printed with inkjet now but most are still screen printed. Other examples of basic screen printed conductive inks in cars are the radio antennas. Many are printed along the edges of windshields under the black or dark red shading areas that cover the gasket material (which are also mostly still screen printed).  Much of what used to be wiring under the dashboards of automobiles, connecting the instrument lighting and other components are now flexible polyethylene film with screen printed conductive pathways. These changes, which are not brand new, are constantly improving as both the metallic ink chemistry and the plastic substrate improve.

One of the first conductive inks, screen printing plants I ever visited was printing silver-based conductive circuit traces on ceramic circuit boards for anti-lock brake systems. I thought that was quite novel until I saw the screen printed electronic automotive gauge division, where the anti-lock circuit board printers did their training, three weeks later. These were electroluminescent. They glow in the dark when power is applied. They were not simply backlit with little light bulbs like older automotive gauges always had been. Was I intrigued? I was floored! I always knew that most automotive dash instruments were screen printed. That’s how the numbers (the ones I don’t pay attention to) get there. I had also already seen electroluminescent dials and instruments starting in the late 70’s (think about your Indi-glow clock). What I had never really put together was the fact that these were not just gauge faces that had graphics screen printed and then stuck onto some miracle electronic glow-pad. That glow-pad…..the electroluminescent circuit part itself…..is screen printed. The learning curve was fast and uphill from there.

Aside from the myriad of other non-electronic components on modern cars that are screen printed (logos, faux-wood grain, decals etc.) virtually every electronic part inside of a modern car that is not actually a physical wire, has some form of screen printing used in its manufacture. About half of the electronic components in a car are using either a conductive or dielectric ink. Many of those printed electronics components that do not use a conductive or dielectric simply used screen printed enamels or epoxies to create patterns on plastics, ceramic or metal.  These substrates are first plated with Tin, Copper, Gold or other metals, then screen printed with patterns and then etched by acid, caustic base chemicals or abrasives to form circuit patterns. It’s getting deeper in here and I have not even gotten out of my car yet. I haven’t even touched on (and won’t get to) the screen printed adhesives that hold panels and components together or the sheets of laminated, screen printed, vacuum-filled ceramic micro-spheres that are used to create certain types of sound deadening and insulating materials.

I’m out of my “print-mobile” and in the kitchen now.  I am literally surrounded by screen printed products and much of them use not only conductive and dielectric inks but inks who special chemical properties allow for extreme water, chemical and heat resistance.  The control panel face or graphic overlay of virtually every appliance in your house is screen printed. Even deeper than that, underneath every one of those soft touch buttons on your stove, microwave oven, food processor and for that matter, television remote, cell phone, I-pod, computer and virtually every other device with switches and keypads……is a multilayer screen printed membrane switch using conductive inks and sometimes even screen printed adhesives, spacers dielectric masks, resistors, capacitors and LED’s.

If all of these screen printed electronics are starting to make your head spin and give you shortness of breath, it doesn’t stop yet. When you get to your doctor, most of the control panels, circuits and electrolytic sensors of many of the devices they connect to your body are screen printed (some also use pad, digital and flexographic printing as well). Hopefully the anxiety of all of this will not drive you to shoplifting at the local drugstore. Many of the products on store shelves have screen and flexographic printed, anti-theft, RFID (radio frequency identification) antenna tags on them made from conductive inks. Yes, sadly when that lands you in jail, even your county prisoner ID bracelet will probably be part or completely screen printed. Probably in the same shop that makes your license plates and prints your orange coveralls.

So back to the chemistry set. With so many forms of digital inkjet printing, why are so many products still being screen printed and why are so many new products choosing screen print? It’s a combination of the ability of screen printing to deposit particles of virtually any material and size, in very precise unbroken layers……and the chemistry. It’s a constantly renewing food chain.  As specialty ink particles, additives and pigments evolve to create different products, eventually these particles or additives change the ink rheology and printability enough that the screen printing process no longer works well to keep making a specific product properly. Metallic and conductive inks have this problem. The metallic or functional particle content of the inks will change enough that the inks no longer print normally with screen print. In most cases the printing techniques themselves first evolve to fix this problem (better squeegee, mesh, set-up and stencil techniques). As the design of the printed product evolves from those processing changes (small, thinner, lighter, cheaper and more durable) the chemistry of the ink evolves again to simplify the process and the evolution starts over.

It is the ability of screen printing to adapt to virtually any ink chemistry, particle type and deposit thickness that keeps it constantly reinventing itself. If you are a professional or printer in the wild-wild-West of Screen and digitally Printed electronics, you already know far more about all of this than what I wrote here so I expect to see you all at the 2010 SGIA printed Electronics and Membrane Switch Symposium. For the rest of you, when the big one finally comes, all that will survive is chemicals, cockroaches and screenprinting, working together for you.

Submitted by: Ray Greenwood, SGIA