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62 PCB007 MAGAZINE I JUNE 2022 ricators is that cupric chloride is incompati- ble with most metallic resists. For this reason, cupric chloride etching is oen dedicated to the manufacturing of inner layer PCBs. Alkaline is on the opposite end of the spectrum because it can be used with most metallic resists, but it has a drawback of being incompatible with many alkali strippable photoresists (dry film). Since these etchants cover two completely dif- ferent ends of this spectrum, most PCB man- ufacturers will adopt both etchants into their etch shop so they can make both inner and outer layers. Summary Each etchant clearly has their own strengths and weaknesses. Table 2 shows a side-by-side comparison of the differences between the two etchants. From Table 2, it can be concluded that cupric chloride may be the better etchant to go with if you are given the choice. With its simplicity in chemistry and required maintenance, it makes up for any of its shortcomings. Using alkaline etchant does not seem necessary unless you are a PCB manufacturer who is running pro- duction every day, needs tight lines and spaces on your PCBs, and/or needs to use metal- lic resists. If that does not describe you as a PCB manufacturer and yet you still desire to use alkaline, it is recommended that you get a chemist or process engineer experienced in maintaining the alkaline etch chemistry. PCB007 References 1. "Process Guidelines for Alkaline Etching," Chemcut.net, October 2001. 2. "Process Guidelines for Cupric Chloride Etch- ing," Chemcut.net. 3. "Happy's Tech Talk: Regeneration of Copper," by Happy Holden, PCB007 Magazine, May 2022. Christopher Bonsell is a chemical process engineer at Chemcut. To read past columns or contact Bonsell, click here. Researchers have pioneered a technique that can dramatically accelerate certain types of com- puter programs automatically, while ensuring pro- gram results remain accurate. Their system boosts the speeds of programs that run in the Unix shell, a ubiquitous program- ming environment created 50 years ago that is still widely used today. Their method parallelizes these programs, which means that it splits program com- ponents into pieces that can be run simultaneously on multiple computer processors. This enables programs to execute tasks like web indexing, natural language processing, or analyzing data in a fraction of their original runtime. The system also makes it easy for the program- mers who develop tools that data scientists, biolo- gists, engineers, and others use. They don't need to make any special adjustments to their program commands to enable this automatic, error-free par- allelization, adds Vasilakis, who chairs a commit- tee of researchers from around the world who have been working on this system for nearly two years. This new system, known as PaSh, focuses on pro- gram, or scripts, that run in the Unix shell. A script is a sequence of commands that instructs a computer to perform a calculation. Correct and automatic par- allelization of shell scripts is a thorny problem that researchers have grappled with for decades. (Source: MIT News) Faster Computing Results Without Fear of Errors

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