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AUGUST 2024 I PCB007 MAGAZINE 29 so the standard controls with most stripping equipment are adequate for the process. One can use pH control to extend the time between stripping bath changes, but this has caused maintenance problems in the past; pH is now used mainly to monitor the bath. Most opt for a simple panel counter to add fresh stripper to the bath every few panels. As with the developer, make sure to check the pH probes daily with an independent meter, and run breakpoint panels every day before use. e takeaway is that you don't need to spend much time worrying about super-tight con- trols for developing and stripping equipment. e working windows for the process parame- ters are wide enough that the standard controls with the equipment will provide all the neces- sary control. PCB007 Don Ball is a process engineer at Chemcut. To read past columns or contact Ball, click here. 10.8. is is good enough to maintain a steady conveyor speed and development rate. Some things need to be checked even with a pH controller. Most people are unaware that the developer solution can buffer aer a while, which means it will read the same pH no matter what state the bath is in. e only sign of this will be undeveloped resist on the panel, even though the pH appears to be in the correct operating range. To prevent this, one should check the pH oen with an indepen- dent meter and the probe recalibrated if the divergence is too high (although a person with one pH meter always knows what the pH is; a person with two pH meters is never sure). Run- ning a breakpoint panel daily before use is also necessary, regardless of the pH meter reading. Like the developing process, the stripping process has generous working windows for most process parameters. Most dry film sup- pliers recommend a 50% breakpoint for clean resist removal, but ±10% makes little differ- ence. Minor deviations in conveyor speed, spray pressure, or bath temperature have lit- tle effect within the 40-60% breakpoint range, Electronics that bend and stretch need batteries with similar properties. Most researchers who have attempted to build such batteries created them with woven conductive fabric or rigid components folded into expandable shapes, similar to origami. But for a truly malleable battery, every part—the electrodes that collect charge and the charge-balancing middle elec- trolyte layer—must be elastic. Now, researchers in ACS Energy Letters report a lithium- ion battery with entirely stretch- able components, includ- ing an electrolyte layer that can expand by 5000%, and it retains its charge storage capacity after nearly 70 charge/ discharge cycles. So far, truly stretchy battery prototypes have moderate elasticity, complex assembly processes or limited energy storage capacity, especially over time with repeated charging and discharging. The latter can be due to a weak connection between the electrolyte layer and electrodes or instability of the fluid electrolyte, which can move around when the battery changes shape. So, rather than using a liquid, Wen-Yong Lai and cowork- ers wanted to incorporate the electrolyte into a polymer layer fused between two flexi- ble electrode films, to create a completely solid, stretchy bat- tery. (Source: ACS) Completely Stretchy Lithium-ion Battery for Flexible Electronics