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PCB007-Dec2023

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84 PCB007 MAGAZINE I DECEMBER 2023 Ferric chloride is a dirty etchant when etch- ing copper and steel alloys. e sludge con- sisted mostly of insoluble metallic chlorides from the alloying metals in the steel. Free acid levels are difficult to determine in ferric because the alloying metals interfere with the acid titration. Even when the free acid levels are properly maintained there are always insol- uble chlorides precipitating from the etch solu- tion to the bottom of the sump. It is generally recommended that the etcher be drained at least once a month and the bot- tom of the sump hosed out. In this case, the etchant was used as long as possible, then drained and the sump filled with new etchant but w ithout ho sing out the bottom (it took too long). More than a week of production was lost simply because they did not want to spend an extra 10 minutes cleaning out the bottom of the etch sump every time they refilled the etcher with fresh etchant. And so it goes. Every equipment supplier can probably come up with many stories of major problems and expenses caused by failure to do even minimal equipment maintenance in the name of getting more product out the door. e time spent devising and running even a minimal daily check and maintenance pro- tocol will quickly pay for itself by reducing downtime caused by easily preventable fail- ures. It may be difficult to think about drain- ing the swamp when you're up to your butt in alligators; just remind yourself that when the swamp is drained, the alligators tend to disap- pear. PCB007 Don Ball is a process engineer at Chemcut. To read past columns or contact Ball, click here. free acid. is meant that the cuprous chloride byproduct from the etch reaction was not being kept in solution by the free acid and was pre- cipitating to the bottom of the etch sump. e ORP, which is a ratio of cupric ions to cuprous ions in the etch bath, continued to increase as cuprous ions were removed from the etch solution. us, the regeneration unit did not add oxidizer or HCl to the system to regener- ate the cuprous ions back to cupric ions. As the concentration of cupric ions decreased, so did the etch rate. Over the weekend, as the bath cooled down, any remaining cuprous chloride finished precipitating out of the etch solution to the bottom of the etcher sump, block- ing the pump intakes. Why did the free acid drop so much? The main- tenance person responsible for checking the acid supply drum for the regeneration system took that Friday off and no one else was respon- sible for checking the drum. By the time the problem was diagnosed, and remedies taken to redissolve the cuprous chlo- ride and bring the chemistry back into specifi- cations, the customer lost four days of produc- tion simply because they did not have a main- tenance protocol to check the free acid level at least once in the morning and once in the early aernoon. A somewhat similar problem occurred a few months ago to a customer etching copper and steel using ferric chloride as the etchant. We got a panicked call one day saying that the heaters in the etcher had "blown up" and they needed someone there immediately to identify the problem and fix it. e problem was evident once the ferric chloride was removed from the etcher. ere was six inches of muddy brown sludge in the bottom of the sump that covered the heaters, causing them to overheat and short out in a rather spectacular fashion. It is generally recommended that the etcher be drained at least once a month and the bottom of the sump hosed out.

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