Hi, Daan,

The old MIL-PRF-55110 permitted a reduction of up to 20% on the minimum
conductor pattern width for etching roughness, pin holes, etc. This is bang
on the 12 mils to 9.6 mils reduction you're uncomfortable with, and I would
be too.

I used a fab house once that ADDED this 20% to the designed width so they
could lose it later in their processing - result was that the conductors
ended up too wide and the spacing between too narrow. Another fab house
managed to reduce some pad widths to half of what they should have been
because of uneven copper plating. All were rejected.

Don't have my IPC spec to hand to see what that says, but I remember it
being much stricter in its requirements.

Peter




                    "d. terstegge"
                    <[log in to unmask]        To:     [log in to unmask]
                    GROUP.COM>                       cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by: TechNet                 Aero/ST Group)
                    <[log in to unmask]>                Subject:     [TN] Tolerance on padwidth


                    02/04/02 06:33 PM
                    Please respond to
                    "TechNet E-Mail Forum.";
                    Please respond to "d.
                    terstegge"






Hi Technet,

IPC-6012 mentions "when not specified on the master drawing the minimum
conductor width shall be 80% of the the conductor pattern supplied in the
procurement documentation".
This is fine for the tracks, but it may cause problems with the solderpads.
Quite often I see that the 12 mil designed fine-pitch pads have a width of
only 9.6 mil on the actual products, leaving a marginal process window for
assembly.
I can live with 11 mil instead of 12 mil, but 9.6 mil is too small for my
taste. The questions:
1)   Is there an additional specification for the etching tolerance of the
solderpads ?
2)   If we put additional requirements on the master drawing, what would be
an acceptable value ?

As always I'm very interested to hear your comments,

Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net

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