Whether an experienced user or a newcomer, people are always asking us how the Vis-U-Etch
process works. To start out, let's assume that you do not have a cupric chloride regeneration controller. With a fresh batch of cupric chloride, you start running panels through your etcher. After a short time, you notice the solution gets darker (more opaque). You also notice that the etch rate is slowing. Not having a controller, you realize that your etchant needs either acid or oxidizer or both for replenishment. A sample of etchant is removed from the etcher in a beaker. First you try adding acid to your sample to see if there is a color change. If the clear green color returns, you add acid to your etcher sump for replenishment. If no color change occurs, the sample is returned to the etcher. Taking a fresh sample from the etcher, this time you add oxidizer to see if the clear green color returns. Again, if this is correct, the sample is returned to the etcher and oxidizer is then added to the sump for replenishment. If no color change occurs in your sample, you then add acid as well. At this point a cor change will occur back to clear green. The sample is then returned to the etcher and both acid and oxidizer are added to the sump alternating back and forth between so as not to have a sudden release of chlorine gas. While this method of testing etchant is going to tell you which chemical(s) is/are necessary, it is not very practical to let your etchant vary that much between regeneration cycles nor is it practical to pay someone to stand there and watch it either. As to the addition of acid first, experience shows that when oxidizer is added and not necessary, some lightening will occur due to simple dilution whereas with acid, no color change will occur at all if it is not needed.
 When connecting a Vis-U-Etch to your etcher, this all becomes automatic. The Vis-U-Etch constantly monitors your etchant, "looking" for any darkening of the solution through the use of the input light cell. As the etchant starts to darken slightly, the regeneration cycle starts. As you would, the Vis-U-Etch tries the addition of acid first and "watches" for the result through the output light cell. If no color change occurs within 7 seconds, the Vis-U-Etch switches to oxidizer and again "watches" for color change through the output light cell. If no color change occurs within 7 seconds, it's back to acid. If the color change occurs with either chemical, the 7 second timing cycle is stopped and that chemical is added continuously until regeneration is completed (the input light cell indicates clear green) or the color change stops (output light cell indicates dark) and the other chemical is again tried. Since the etchant is monitored continuously, the variation in the color of your etchant is almost unnoticeable. This also means that your etchant is very tightly controlled.

 Let's look at what is happening chemically. From a simple perspective, the etchant can exist in several forms:

 cupric chloride
 cupric hydroxide
 cuprous chloride
 combination of above

 Cupric chloride is a clear green color and does the etching. Cupric hydroxide is a cloudy (opaque) green and requires the addition of acid to become cupric chloride. Cuprous chloride is a dark green and requires the addition of oxidizer to become cupric chloride. With a combination of cupric hydroxide and cuprous chloride, the etchant is now a cloudy dark green and requires acid to convert the cupric hydroxide to cupric chloride (partially lightening the etchant sample), and oxidizer to convert cuprous chloride to cupric chloride (partially lightening the etchant sample). When we were originally testing our sample in a beaker, we determined what we had by determining what was needed to return our etchant to the clear green cupric chloride state. From a Vis-U-Etch standpoint, it performs the same color test, addition of chemical when necessary and retest as you would. The difference between you and the Vis-U-Etch is that the Vis-U-Etch monitors the etchant continuously ensuring tightly controlled etchant while you would be sampling etchant occasionally causing wide variations in etchant state resulting in a non-uniform etch factor and etch rate.

What about Baume (sg), ORP and Normality?

 Spent cupric chloride (waste?)

Currently in the state of California, spent etchants are considered hazardous waste and are thus
required to be manifested. The sad part about this is that etchants are not waste to the companies that pick it up for recycling. To them spent etchant is a raw material to be used in the manufacture of a new product. Fortunately, the Federal and many State Governments have concurred with the recycling companies that these spent etchants are in fact raw materials used in the manufacture of a new product. Therefore, in more and more places, spent etchant can be collected under a Bill of Lading instead of being manifested as hazardous waste.

Ammoniacal vs. Cupric Chloride

Recently on the Internet and elsewhere, there has been a great deal of debate surrounding which is the better etchant. In our customer research, we have determined that of those board shops using both ammoniacal and cupric chloride etchants, the cost of using ammoniacal etchant is approximately 2 and a half times more expensive than cupric chloride. If this is the case, why use ammonia? The answer: Some processes can not be done in cupric chloride. If your company uses the pattern plate / strip / etch / solder strip process, ammoniacal etchant must be used due to the fact that cupric chloride will remove the tin or tin / nickel pattern plate applied as well as all of the copper. This pattern plate process is more expensive than panel plating and has its own problems with uniformity, etc. Panel plating / tent and etch is perfect with cupric chloride. Panel plating is far less expensive than pattern plating and thus contributes indirectly to the lower cost of cupric chloride. What about Gold plated boards? This can and is being done using cupric chloride. In fact, most of the noble metals can be used as an etch resist provided that they are pure (not an alloy) and plated sufficiently as you would using any other etchant. What about fine line etching? With very little effort and the most basic equipment, line and space sizes down to 6 mil can easily be achieved using cupric chloride. By using collumated light in the imager, more spray nozzles, independent oscillation of the spray bank from the conveyor and higher nozzle pressure in both the developer and etcher, 1 mil line and space can easily be achieved using cupric chloride. Since most of our customers that have both ammoniacal and cupric chloride do approximately 70% to 80% of their etching in cupric chloride, it stands to reason that the lower cost and lack of strong odor while etching are major factors.