Issue link: https://iconnect007.uberflip.com/i/1330321
JANUARY 2021 I PCB007 MAGAZINE 65 visible light spectrum. There was a push for the UV or the non-visible light spectrum. We're talking maybe 3-micron micro-mirror size DMD and go from visible light to UV light. With the DI manufacturers, we all quickly adopted the same engine because it's finally been brought into the UV spectrum, which takes some do- ing. The analogy to that is how inkjet systems were not developed inside the PCB industry. These have been in use for many years—more than a decade. These systems have been used in the solar industry for printing, and it has been used in the masks in the semiconductor market. For example, there is a German company that has been using inkjet for at least a decade in the semiconductor and solar panel markets. They have adapted this to PCB because they see a future, saying, "We'll take our technolo- gy which we're very familiar with, and go into the PCB market." It's a peripheral market, but it's not like the PCB companies have been de- veloping this technology. Now it will go into other markets; has already been in many mar- kets. It's finally perfected to a point where you could use it in PCBs in terms of its resolution capability. Holden: I didn't realize there's a change when you go from the visible light to the ultraviolet for those engines. Carignan: Definitely. You're familiar with what the chips look like. That's a very special glass that tends to solarize under UV light. Solariza- tion is a phenomenon where if you expose a standard non-glass, such as a soda glass, to UV light for any period of time, it solarizes. Even- tually, you get no light transmission because it just creates a film, if you will. DMDs for UV light are such a big deal because it's an entire- ly different glass window. One company must place gases under the window and seal them in to stop all the solar- ization. If you just grab the visible light chip and start using it at 360 nanometers, the light intensity declines rapidly. These are very spe- cialized chips, and there are very specialized techniques to be able to use those chips. Holden: There was software in the camera sys- tems to figure out where the holes were for registration. Has that been duplicated by oth- ers in the direct exposure area? Carignan: Yes, they all have it now. You won't be able to buy a system without it. You acquire the image by fiducials with high-resolution camera, but the important part is with the soft- ware not moving the motion control to where the fiducials are. The trick—the evolution of that—became how to do linear scaling so that you could take an image quickly. This is not as easy as it sounds, but you rip an awful lot of data. Immediately, on every side, you want to print and measure a bunch of fiducials. Then, you're going to stretch that data, re-raster it, and print it. You're not going to want to wait 10 minutes while the computer is thinking about how to re-raster all these files. When I started at this, I might wait for five minutes on every side. The results were good, but mostly the machine was thinking. Most of that improvement comes through using quad cores and multiplexing—each channel doing its own data rastering. It's amazing, but that process takes one to two seconds and usual- ly happens in the background. It rasters while it prints. That was like an evolutionary part of digital imaging. If you had a very early ma- chine, you'd say most of the time the machine is thinking. Now, it all happens within sec- onds. Also, it's easy to envision a scaling of the data in X and Y, but oftentimes, your panels— particularly on rigid-flex panels—look more like a rhombus or a nonlinear error correction. It's actually quite hard to do because you have to match what you see from the cameras to preset libraries of curves, like third order equa- tion curves. Then, you have to pick an equa- tion that distorts the data, so you get perfect registration. You need to do all this within sec- onds. It's very subtle and not as well-known or published just how much has been done on the software side to get the amazing amount of registration, regardless of what the image of