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November 2001

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Subject:
From:
"<Peter George Duncan>" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 21 Nov 2001 17:52:58 +0800
Content-Type:
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Hi, Steve,

The number of track repairs allowable is normally a matter between the
contractor and the customer and depends to some extent on the design and
its operating environment. I once had a customer who insisted on reviewing
the situation if the number of track repairs, cuts or jumpers went above 3,
and the board had to be re-routed if the number of track mods exceeded 5.
On the other hand, I have seen customer-owned card assemblies with a
veritable wiring harness of repair and mod wires, so there are no fixed
rules.

You have to assess the situation on its own merits, rather than relying on
specs to tell you the road out. All things being equal, though, if the
repairs are carried out well to a spec such as IPC-7721, and they don't
interfere with, or reduce the reliable mountability of components, you
should not have much of an issue. Having said that, and not knowing the
extent of the track repairs being proposed, I would not like to accept new
boards with long stretches of repaired track (greater that, say, half an
inch) or more than about 6 repairs, but that's just my personal view.

It's not always an easy call to make, but discuss it with the designers,
the customer if need be, and the assembly line. Repaired tracks are weaker
than original track, and this must be borne in mind for processing as well
as reliability in the field. If in doubt, let the fab house repair one or
two (best and worst case) and see how they fare through the production
cycle. Then you can better determine what level of repair you can accept.

Good luck!

Peter Duncan




                    Stephen Brown
                    <[log in to unmask]        To:     [log in to unmask]
                    RATEX.COM>                  cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by: TechNet            Aero/ST Group)
                    <[log in to unmask]>           Subject:     [TN] Raw Card Track Repairs


                    11/21/01 04:26 PM
                    Please respond to
                    "TechNet E-Mail
                    Forum."






People.

We get our PCB's assembled to IPC-610 class 2. We have recently been
approached by our vendor regarding track repairs on our raw cards. Now I
personally am not keen on allowing this, but is there a standard for raw
cards similar to 610 which states an allowable quantity of track
repairs, if any?

Regards.

Steve Brown.
Commodity Specialist
Xyratex.

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