Homebrew PCBs

-------- ORIGINAL MESSAGES:   

Date: Fri, 04 Feb 2005 09:46:09 +0100
   From: "Stefan Trethan" <stefan_trethan@...>
Subject: Re: Re: Home PCB kit

On Fri, 4 Feb 2005 03:28:39 -0500, Thomas P. Gootee <tomg@...>  
wrote:

>
> Hmmm...  Well...  OK.   But I routinely use 6.67/1000ths-inch  
> (2/300ths-inch) tracks and spacing, with toner
> transfer, with very close to a 100% success rate. I have also routinely  
> used 6.67/1000ths-inch tracks (2/300ths-
> inch) with 3.33/1000ths-inch (1/300th-inch) spacing, with no problems  
> (with an HP LJ 4 @ 600DPI, in both cases).
> And, in very-limited tests, I have even had almost 100% success with  
> 1.67/1000ths-inch tracks (i.e. 1 dot wide
> printed with an HP LaserJet 4 at 600 dots per inch (i.e. 1/600th-inch  
> wide, on screen), with HP toner on
> Staples' "Picture Paper", as before) (but unfortunately didn't test the  
> same size-range for the spacing limit).
> Tom Gootee


- Good to hear there is still some room in it. My HPIIID just isn't up to it.

- Don't you have problems with toner spreading? if i make a 10mil track and  
- 10mil space they turn out not exactly the same width.

- ST

----------Current RESPONSE:

Stephan,

Yes.  It does look like there's still room for better toner transfer performance, i.e. smaller and closer traces and pads.

But yes, I DO have problems with toner spreading.  But I usually EITHER use large-enough spacings for trace separation (2/300ths-inch seems like about the minimum, to have basically no worries about developing a short between two 2/300ths-inch-wide traces), OR only use 1/300th-inch spacing where it won't really matter too much if a short develops, such as when I have several parallel traces that all return to a common ground point, which might have small (1/300th-inch) spacing when they are getting close to their common connection point.  (Gee, I almost hope that someone asks me WHY I would want to run multiple ground traces, in parallel, when they're all going to the exact same place, anyway; heh heh.)

I remember trying some surface-mount types/sizes of patterns, once, just as a test, and having some very close-together pads that I tried to run traces between, which really had problems from toner-spreading.  I think I was using pads that were 7x14 dots, at 600 dpi, with 7 and 8 dots spacing tried, between some of them, and tried putting one and two traces between them (e.g. two one-dot-wide lines at dots 3 and 6 of an 8-dot space).  I guess a solution might be to allow some space for the toner spreading, i.e. draw the pads narrower.

-Tom Gootee

http://www.fullnet.com/u/tomg/gooteepc.htm

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