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OCTOBER 2024 I PCB007 MAGAZINE 77 width specifications while the panels exposed in our lab and passed through the new DES line all passed with flying colors. A technician from the exposure unit supplier was reluctantly called in and, aer careful test- ing, found a slight crack in the vacuum line. Sometimes it sealed itself when the vacuum was drawn and gave the phototool good con- tact with the etch resist. Sometimes the crack didn't seal tightly, allowing some slight off-con- tact with the resist even though the pressure gauges said the seal was good. at vacuum line was replaced, and everything was good. You may wonder how they got good pan- els off the other developer if the exposure unit was the problem. Well, the other DES line had a different exposure unit, something I should have checked but didn't think of. I could have saved a lot of travel time (six hours each way) if I had thought about it. Conclusion I have many more such examples, but the point is to think rationally when confronted by a process problem and not succumb to the urge to panic and throw every possible solution at it, hoping one of them will work. Contact your suppliers (and not just your equipment suppli- ers); they've probably seen more weird prob- lems than you can imagine and may have some insight. Finally, remember that these process problems don't just jump out at you for no rea- son. ere is a cause that can be found and fixed if you use reason and logic. PCB007 Don Ball is a process engineer at Chemcut. To read past col- umns or contact Ball, click here. Researchers at EPFL have discovered that by shining different wavelengths of light on a material called magnetite, they can change its state, making it more or less conducive to electricity. Magnetite is the oldest and strongest natural mag- net. It is used in electronics and has unique proper- ties that have made it interesting in the field of spin- tronics—devices that run on the spin of electrons rather than their flow (which is what we know as elec- trical current). Beyond all that, magnetite has played a crucial role in understanding magnetism, attracting the interest of Einstein and other famous scientists. Recently, research on exploiting its out-of-equilib- rium switching properties has gained momentum, highlighting its potential for advanced technologies. "Some time ago, we showed that it is possible to induce an inverse phase transition in magnetite," says physicist Fabrizio Carbone at EPFL. "It's as if you took water and you could turn it into ice by put- ting energy into it with a laser. This is counterintui- tive, as normally to freeze water you cool it down, which means you remove energy from it." Now, Carbone has led a research project to elu- cidate and control the microscopic structural prop- erties of magnetite during such light-induced phase transitions. The study discovered that using spe- cific light wavelengths (colors) for photoexcitation the system can drive magnetite into distinct non- equilibrium metastable states ("metastable" means that the state can change under certain conditions) called "hidden phases", thus revealing a new pro- tocol to manipulate material properties at ultrafast timescales. (Source: EPFL) Controlling Electronics With Light: The Magnetite Breakthrough