Mr. Gendreau makes a good point. Copper edges always have been allowed.
There is section 3.3.8 that allows on Class 3 boards a .031"  gap between
the gold of an edge connector and a tinned trace.
I don't see a picture of this in IPC-A-600.
There is a picture of skipping solder mask which is allowed on Class 1 (
shows bare copper), but not on Class 3.

Maybe the big question is " are they going to conformal coat the board after
assembly?".
There has always been the added expense for SMOBC of stripping all the tin
off and then HASL. This was done because the Military believed the exposed
copper would be a reliability problem because the trace would corrode away.
Where tin plated copper runs and component leads would last for 20 years.
Steve Bakke C.I.D.
President , Midwest Chapter, IPC Designers Council.


        ----------
        From:  C. Don Dupriest [SMTP:[log in to unmask]]
        Sent:  Tuesday, September 05, 2000 9:10 AM
        To:  [log in to unmask]
        Subject:  [IPC-600-6012] FW: Exposed copper
        Importance:  High

        Greetings all,
        We have an urgent request from a 6012 user.  Product is being held
up for
        shipment.

        The email below and attached photo is a request for interpretation
        concerning a manner of exposed copper.  Does anyone recall the
original
        thinking behind the 3.5.4.6 on how to property apply the percentage
of
        conductor surface.  My notes show no prior discussion on this
paragraph.
        See the question below in the original email.

        I believe the cause resulted from a combination of selective tin
strip and
        solder mask clearance.   A small portion of the conductor is exposed
with
        bare copper.  Touchup would be cost prohibitive.  Does the specified
        paragraph best cover this issue?  Anyone crossed this bridge before?

        " 3.5.4.6 Final Finish Coverage Final finish shall meet the
solderability
        requirements of J-STD-003. Exposed copper on areas not to be
soldered is
        permitted on 1% of the conductor surfaces for Class 3 and 5% of the
surfaces
        for Class 1 and Class 2. Coverage does not apply to vertical
conductor
        edges. "

        The bottom line is: "is this an acceptable condition"??????

        Please reply to "all" to capture the discussion.

        Thanks, hope everyone will be able to make Miami next week.


                C. D. (Don) Dupriest
                Lockheed Martin Missiles and Fire Control - Dallas
                Electronics Manufacturing Engineering
                Mgr. - PWB Process Development
                Ph. 972/603-7724 fax: 972/603-3548
                Email: [log in to unmask] <mailto:[log in to unmask]>


        ----------
        From:  Cirtech [SMTP:[log in to unmask]]
        <mailto:[SMTP:[log in to unmask]]>
        Sent:  Friday, September 01, 2000 12:13 PM
        To:  [log in to unmask] <mailto:[log in to unmask]>
        Subject:  FW: Exposed copper




        -----Original Message-----
        From:   Mark Alexander
        Sent:   Friday, September 01, 2000 8:30 AM
        To:     'Don Dupriest'
        Subject:        Exposed copper

        Don,
        I've attached a picture of an area that is typical of an exposed
copper
        area. This is The trace that leads into a SMT pad that is not
covered by
        soldermask. The actual dimension of exposed copper is approx. .003
to .005
        mils. According to ipc-6012 section 3.5.4.6 there is an allowable
amount of
        exposed copper of 1% or 5% depending on what class the board is
called for.
        My question is, how do you calculate this. How do you translate 1%
or 5% of
        conductor surfaces. Is it total square inches of copper on board
multiplied
        by 1% or 5%? If so then the formula for a board with a total of 5
square
        inches multiplied by 1% = .050". What then do you do with the
.050'.? If it
        was 5% then = .250'. What do you do with that?
        Please fill me in
        Thanks,
        Mark Alexander
        Engineering Mgr.
        Cirtech Inc.
        Orange, Ca.
        714-921-0860 ext. 220
         <<copper.bmp>><<File: copper.bmp>>