> Using thin track as fuse is a well-known bad idea, precisely because of
the
> problems noted above plus a few, though, again, even bad ideas can have
> their day.
Thin tracks work OK as a fuse if you size them (track width, copper weight,
AND plating thickness) correctly. You don't have to throw the board away if
you also take the effort to put a leaded fuse (i.e. picofuse) footprint on
the board and connect both pads together with the fuse track. If some bozo
blows the track, just solder a leaded fuse across the footprint to repair
the board. Simple, cheap (free until you blow the track), and effective.
Best regards,
Ivan Baggett
Bagotronix Inc.
website: www.bagotronix.com
----- Original Message -----
From: "Abd ul-Rahman Lomax" <[EMAIL PROTECTED]>
To: <Protel EDA Forumm>; <[EMAIL PROTECTED]>
Sent: Thursday, June 14, 2001 10:27 PM
Subject: Re: [PEDA] AW: Spiral trace construction?
> At 01:15 PM 6/14/01 -0500, David Cary wrote:
> >In my case, I
> >finally got enough documentation to prove that PWB traces varied in
resistance
> >far more than the 1% we wanted in our current-sense resistor. (Mostly due
to
> >variations in the tin plating over copper, I hear).
>
> Actually I'd be surprised if that was the major contributor. This is an
old
> figure, but Lund shows a thickness on 1 ounce copper thickness of 35
+10/-5
> um. That is a *huge* variation for a sense resistor. There is also the
> problem of etch control which would affect the width of a trace, but the
> thickness variation would be a much larger error source. Add to that the
> plating variation: It appears that foil plus plating on a 1 ounce plated
up
> 1 ounce board is specified as not less than 35 um. The maximum does not
> seem to be a matter of concern, as long as the board meets other
requirements.
>
> But half ounce copper was specified as 17.5 um +/- 5 um. That's a little
> better, and plating could be avoided in various ways. Still, the
resistance
> is going to vary by +/- 35% or so.
>
> That might be usable as a sense resistor, even for accurate measurements,
> if it could be trimmed or calibrated. The variation of resistance with
> temperature would need to be considered. There might be applications where
> this would make sense.
>
> Using thin track as fuse is a well-known bad idea, precisely because of
the
> problems noted above plus a few, though, again, even bad ideas can have
> their day.
>
> [EMAIL PROTECTED]
> Abdulrahman Lomax
> P.O. Box 690
> El Verano, CA 95433
>
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/subscrib.html
* - or email -
* mailto:[EMAIL PROTECTED]?body=leave%20proteledaforum
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Browse or Search previous postings:
* http://www.mail-archive.com/[email protected]
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
