Etchant Control/Monitor FAQ's

Our process and etcher give good boards without scrap or rework with etchant density anywhere in a range of +/- 0.5 degrees Baume from the set point. Why should I want a controller any better than +/- 0.5 degrees Baume?

  If your goal is to prevent scrap then your process monitor should alarm before your +/- 0.5 degrees Baume threshold for scrap is reached. You should want the alarm levels at +/- 0.3 degrees Baume to give some safety margin. In order to prevent annoying false alarms the process controller should keep the system well away from the alarm level in normal operation. Thus you need a control good to better than +/-0.2 degrees Baume for a process that can tolerate +/-0.5 degrees Baume worst case. Then the process monitor will sound a valid alarm before scrap boards are created.

Our process etchant control doesn't have monitor and alarm functions. What are we missing?

  Without continuous process monitoring your first indication of chemistry problems is likely to be a scrap board coming out of the machine. At this point there may already be eight more already etched boards behind it in the etcher. This can be very expensive. This means up to 4600 square inches of boards have been ruined if an alert operator catches the first bad board that comes out. At the final etch stage of the process boards have from $0.10 to $1.00 per square inch invested in them. This can be a very expensive way to detect chemistry problems.

Why are Optrol's Control/Monitors packaged in three separate units (Power Module, Control, and Monitor)?

  Each of these functions has distinct mounting requirements. The Power Module needs to be convenient to the line power and replenisher pump power line. The Control needs to have access to etchant solution and gravity drain back to the etcher sump. The Monitor needs to be convenient for the operator. It can be nearly impossible to satisfy all these requirements at a single location on an etcher. It is however very easy to put each piece where it needs to be and then plug them together with the cables provided. This scheme also means that line voltage is confined to the Power Module and exposed to neither etchants nor operators.

What solution chemistry problems do Optrol's monitors detect?

  Replenisher supply, plumbing and pump problems, operator mismanagement, leakage into the sump, defective squeegee rollers, and erratic sump mixing will all trigger the monitor alarm.

Why is Optrol's hydrometer float so large?

  The etchants to be controlled have many tiny gas bubbles similar to soda pop. These will cling to a float and cause a small bouyancy error. To minimize this error the bouyancy of the float volume must be much larger than the variable bouyancy of the surface bubbles. The volume to surface ratio is proportional to the float diameter. We use a large enough float diameter to easily give the +/- 0.1 degrees Baume precision needed.

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