Issue link: https://iconnect007.uberflip.com/i/1534385
from acidic cupric chloride to alkaline cupric chloride (alkaline etch). One may expect double the etch rate and better etch factors (although not necessarily), but not a smoother etch profile. is is more dependent on the physical rather than the chemical parame- ters of the etcher setup. ere are reasons one might contemplate changing etch chemistries but getting a better etch uniformity should not be one of them. Etch factors (the ratio of downward etch to sideways etch, or how straight the sidewalls are) have become more important with the trend toward narrower lines and spaces. Ideas to improve etch factors abound, but here are some of the more common misconceptions that are worth keeping in mind, as they could save you time. Ferric vs. Cupric An early misconception was that etching copper with fer- ric chloride produced better etch factors than cupric chlo- ride. Early on, almost all circuit boards etched copper using fer- ric chloride because that's how it had always been done. As circuit board production increased log- arithmically in the early years, most manufacturers switched to cupric as the etchant of choice because it could be regenerated, maintaining a constant etch rate and greatly reducing disposal costs. Almost immediately, the issue of which etchant pro- vided the best etch factor was raised and still comes up in dis- cussions today. However, in the mid-1990s, extensive design-of- experiment testing with a man- ufacturer of lead frames made it clear there was no difference in etch factor between the two. Later tests with circuit boards confirmed this. Sorry guys, simply switching to ferric chloride for your etch factor-critical boards will not solve your problem. Fan vs. Cone Nozzles Another misconception almost as old as the industry is that using fan nozzles rather than cone nozzles to deliver the etchant to the board surface results in better etch factors. Again, the lead frame tests showed no differ- ence between the two nozzles. A test using fan nozzles to etch from the top and cones from the bottom revealed no difference in etch fac- tor, either visually or microscopically. Again, sorry, but simply switching to a different noz- zle won't solve your etch factor problem. 36 PCB007 MAGAZINE I APRIL 2025