Issue link: https://iconnect007.uberflip.com/i/1525368
42 PCB007 MAGAZINE I AUGUST 2024 Temperature Control All too oen, while process engineers and technicians focus on wet analysis, the operat- ing temperature checks are overlooked. Rins- ing and developing are typical processes that are more effective with tempered rinses. Too frequently, when rinsing uses incoming water (e.g., during the winter months in very cold climates), the water temperature is quite cold unless heaters are in place. An increase of 10°K at temperatures not far from room temp will increase the reaction rate by a factor of 2 to 3 (see chart below). °F °C °K Rate Increase 72 22 295 -- 90 32 305 2-3x (200-300%) 108 42 315 1 ½x (150%) 126 52 325 1x (100%) At some point, the reaction rate increase starts to level off. What's the point? Temper- ature has a significant influence on chemical reactions and rinsing. Summary Certainly, most operators and engineers worry about controlling the wet chemistry of the various processes of the printed circuit board fabrication process. Yet, they are oen surprised and disappointed that the quality of the finished product is not meeting stringent requirements and key workmanship standards. Further examination will find that other, oen overlooked aspects of the process were not controlled and maintained. It only makes sense that in addition to wet chemistry, other non- chemical factors be monitored and controlled. ese include rinsing, filtration, agitation, and temperature controls. Ignore these best prac- tices at your own peril. PCB007 Michael Carano brings over 40 years of electronics industry experience with special exper- tise in manufacturing, perfor- mance chemicals, metals, semiconductors, medical devices, and advanced packaging. To read past columns, click here. Scientists from Tokyo Tech and EM Labs, Inc. report that the dielectric properties of polyimides could aid the development of 6G wireless commu- nication technologies. Using a device known as a Fabry-Pérot resonator, they measured the dielectric constants and dissipation factors of various types of polyimides at frequencies up to 330 GHz. One challenge for both 5G and 6G is that near the terahertz range, signal attenuation and interfer- ence are more prominent; maintaining signal integ- rity becomes much harder. Some of these issues are mitigated by glass- and ceramic-based insulat- ing materials, which currently dominate the scene, but their high cost and fabrication complexity make them unsuitable for mass-produced devices. A research team from Tokyo Institute of Tech- nology studied polyimides (PIs). "Polyimides have excellent thermal stability, mechanical toughness, flexibility, and favorable dielectric properties. But the correlation between the molecular structure and dielectric properties isn't clear," explains Pro- fessor Shinji Ando. " The research team analyzed the dielectric prop- erties of 11 PIs with different molecular structures. They measured the polyimides' dielectric con- stant (Dk) and dissipation factor (Df). All of the 11 PIs showed typical Dk and Df curves. Notably, PIs con- taining higher fluorine content exhibited lower Dk values. Perfluorinated polyimides exhibited signifi- cantly lower Dk and smaller Df than the other poly- imides, with a small frequency dependence of Dk and Df. (Source: Tokyo Tech and EM Labs, Inc.) A Deep Dive into Polyimides for High-frequency Wireless Telecommunications