Homebrew PCBs

DJ Delorie <dj@...> writes:
>
> I've got some preliminary (i.e. unetched) results.
>
> See: http://www.delorie.com/pcb/inkjet/

I looked at a 3200 dpi reflective scan of an LJ4 print very closely in 
Photoshop, printed on the cheap paper I normally use. The results aren't 
good. Some isolated, minor pitting is evident even without adjusting the 
gamma curve. There is also some faint smudging, not significant and also 
ignorable.

I then adjusted the bottom of the curve until it just began to clip the 
blacks, and progressively brought down the highlights. At the point the 
smudging disappeared, assuming etching is similar to a photographic process, 
the board would have been usable at that state. A few more pits became 
visible, but the fine details were still whole and intact. (I use 8 mil/8 
mil rules for most stuff, dropping down to 6/6 only around 0.4 mm pitch 
devices.) Continuing to adjust down the highlights, it began looking like 
the boards and traces I typically make. Pitting became significant in 
places, but not objectionably so until still higher levels of "over-etch". 
At extremes, the over-etch is obvious, and looks surprisingly exactly like 
copper on an over processed board. Many of my problem boards are from 
etching, but I already knew that.

The scanner is an Epson 3200, calibrated using Monaco EZColor. What it sees 
is pretty much what's there to be seen. I could try it again as a 
transparency, but I think I can extrapolate from this the effects of 
over-exposure on photo-resist. The only thing missing is a relative measure 
of the (visible light) transmissive density compared to a Stouffer wedge. 
I'm still curious, but don't have any transparency sheets laying about. (I 
use toner transfer.)

By mere coincidence, I have an HP P2015dn on order (1200 dpi). I'll check 
this again Tuesday when it gets here. (Its purchase is only peripherally 
related to PCBs. I've been wearing out the pavement between here and Kinkos 
the past few months, where I've been sending rather large print jobs. The 
printer will actually pay for itself before the year is out.)

Mike.