fenrir_co wrote:
> --- In Homebrew_PCBs@yahoogroups.com, Russell Shaw <rjshaw@...> wrote:
>
>>derekhawkins wrote:
>>
>>>I'm attempting to debunk the following two myths at the same time;
>>>
>>>1. A collimated light source is needed for .005" to .01" rules
>>when photoetching.
>>>
>>>2. All vertical bubble etching system cause uneven etching. Board
>>size is 6"X4" hung vertically as shown.
>>>
>>>http://www.pbase.com/eldata/6_6_rules
>>
>>I've used a vertical bubble etcher for a few years and have no
>>uneven etching at all. These myths are in the same category such as "ferric
>>chloride is slow", "PRP doesn't work", etc.
>
>
> I've used vertical bubble etchers, both homemade, and commercial (but
> cheaper models), and both of them caused terribly uneven etching. I
> suspect that 1) the strength of the air pump and 2) the size and
> placement of the bubbles have a lot to do with this. So if you have a
> vertical bubble etcher that works perfectly, post the name and model
> number of it. I don't remember where I got the commercial one that I'd
> bought, I think it was Electronics Express but I could be wrong. I
> threw it away about two years ago. It etched much, much faster where
> the bubbles hit the metal, and one edge would etch faster than the
> other. So I don't think this is entirely a myth, I think it has to do
> with the quality of the bubble etcher you buy.
Look at the blue etcher tank on
http://www.kalex.net.auWhen the bubbles rise between the pcb and the tank side, a vacuum forms,
pulling the pcb against it. Then the reverse happens on the other side of
the pcb. This causes the hanging pcb to pendulum back and forth. The bubble
stream is quite weak, but the etching still happens evenly over the whole pcb.
I use ferric chloride 1:1 with water (use hot water for bonus speed if you're
mixing a new batch), and 1/4 - 1/2 cup of hydrochloric acid every few months.
I've been using the same etchant in the tank for the last year. Double-sided
35um pcb etches in 6mins at room temp with fresh etchant. More typically, it's
8-12mins, then put the pcb into a tray and do a small amount of brushing to etch
the last few stubborn bits.