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FEBRUARY 2021 I PCB007 MAGAZINE 67 tion with the ink. Our customers benefit from our expertise with a recommended ink. How- ever, being able to choose between multiple ink suppliers is an attractive feature of our system. In principle, the PiXDRO JETx-M is ink inde- pendent thanks to its highly chemically passive materials and components along the ink path. erefore, if jetting and curing are correct, the machine can print it. However, as you can imag- ine, the inks on the market today and in the fu- ture will contain the most disparate compo- nents. is introduces unknowns and, for what you do not know, you cannot prepare. Luckily, we learned early in the development about such challenges. From that time on, to remain on the safe side and still enable robust processing, we created a material compatibility kit to run stress tests on future alternative inks. is will avoid bad situations like a chemically attacked gas- ket resulting in litres of ink spilling out, more subtle situations like inexplicable shis in per- formances, or sudden increases of maintenance time "to get it working." Negative results from stress tests enact specific changes in the ink path that will hence ensure a robust process. anks to agreements with our components suppliers and the modularity of the system, these data- driven changes are quick and effective. Starkey: Luca, I understand you have devel- oped the in-house capability to characterise and qualify inks. Could you tell us something about how it works? Gautero: At first, a few years back, there were just a couple of available printable, curable inks. So, qualification was only about results repeat- ability. In the last couple of years, however, a wealth of companies stepped up their game and prepared interesting formulations for sol- der mask. Since we are technicians at heart, we started trying some of them. However, aer a first, goofing test, we adopted a rigorous struc- ture of milestones to qualify all these incoming ink alternatives. ree milestones keep it small and simple: Each milestone is the gateway to the next one. e first gateway is information; written documentation needs to cover safety, rheology, wetting behaviour on PCB surfaces, standard operating procedures for printing and maintenance operation (i.e., filling and draining the system as well as the results of the material compatibility kit), and the ink suitability as sol- der mask. For the latter, we refer to tests stated in IPC-SM-840. We know that it is only part of the story, though it's a minimum requirement. e second is the real deal: An R&D print- er in our PrintLab becomes the test vehicle for the ink. Our printing strategies, together with the candidate ink's curing and post-treat in- structions, are applied. e resulting panels (Figure 4) are then characterized, either man- ually or automatically, to define the ink process suitability. e last phase involves the PiXDRO JETx- M in our PrintLab and a commercial aspect. e ink reaching this level is good enough to print, though we ask the material supplier to introduce a willing, independent PCB manu- facturer as supplier of halffabricated large sub- strates and judge of the final inkjet coated sol- der mask. is third party will then, indepen- dently from us or from the material supplier, validate the effort performed so far. Starkey: What parameters determine how an ink will perform in practice? Figure 3: Example of serialization of panels in clear sight, hidden or absent.

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