AMMONIACAL ETCHANT CONTROL QUICK TEST

For Controls Without Digital Display:

A quick way to evaluate the precision of an etchant solution replenishment control is to observe the panel area fed into the etcher during the time the pump is OFF. During that interval the sump is picking up copper from it's lower control value to it's upper control value. For example, if the etcher has an 80 gallon sump and is being fed one ounce copper boards with half copper and half space areas then one ounce of copper goes into the sump from the two sides of a square foot of double sided board. If four 24x24 inch boards turn the replenisher back ON then the 16 ounces of copper added to the sump raised solution copper 16/80 = 0.2 ounces per gallon indicating pretty tight solution control. If on the other hand the etcher handled 40 of these panels before the control turned the replenisher pump back on then the sump accumulated 160/80 = 2 ounces per gallon between pump OFF and pump ON indicating poor precision. For some of the economic advantages of tight solution control see Savings With Good Etchant Control and FAQ.

For Controls With Digital Display:

In addition to the method described above, another way to detect poor precision is to observe the control's density display. Jumps in the displayed value are a tip-off to sensor sticking or sensor instability due to large surface gas bubble releases. The jump values are added to the controller's inherent imprecision to get its total imprecision. Stable digital display readings by themselves are not proof of stable control. Most controllers derive both their control information and their display information from the same density sensor. If that sensor drifts then the control point and a display error drift together so that the displayed number stays constant. It is still necessary to periodically test the solution in a quality control lab to verify control stability. For some of the economic advantages of tight solution control see Savings With Good Etchant Control and FAQ.

Optrol's Control/Monitor Catalog
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