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decap:epoxy [2019/05/13 21:00] – [Light Ray] mcmaster | decap:epoxy [2020/02/27 20:57] – mcmaster | ||
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One problem from this lack of circulation is that it may create pockets of low concentration acid, leading to corrosion. | One problem from this lack of circulation is that it may create pockets of low concentration acid, leading to corrosion. | ||
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+ | ===== McMaster live 2019-11-10 ===== | ||
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+ | {{: | ||
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+ | Experiments trying to decap COB while keeping PCB intact | ||
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+ | TLDR best result | ||
+ | - Cut a polypropylene tube (ie from a microfuge tube) roughly the size you want to expose to acid | ||
+ | - Heat tube up to soften it | ||
+ | - Warm PCB | ||
+ | - Attach hot tube to PCB, letting plastic deform into place | ||
+ | - Let cool a little | ||
+ | - Seal outside of tube with silicone | ||
+ | - Let silicone cure | ||
+ | - Decap with gentle heat on hotplate (maybe 160F max) using 2 WFNA : 1 H2SO4 | ||
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+ | Above is a compromise between PP providing the best chemical resistance and silicone providing the best seal | ||
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+ | Silicone only experiment | ||
+ | * Made silicon dam by layering up | ||
+ | * Silicone surface cured, but internally didn't always | ||
+ | * Uncured silicone dissolved in WFNA and floated to top. This then cured and blocked the surface | ||
+ | * Interesting, | ||
+ | * Acid may eventually undermine the PCB, but eating the silicone itself came first | ||
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+ | Someone also suggested I should try PTFE gasket. In the past I had tried kapton which didn't work well (acid tended to wick into kapton). Maybe PTFE would repel acid better | ||