Charlie,
        My ceramic experience is a few years old but here goes.  We had
standardized on 0.035" thick substrates.  Since we had in-house laser
capabilities for active trimming of resistors, we also had lasers for
scoring/scribing.  The scoring process consisted of drilling holes
approximately 1/3 through the thickness of the substrate.  I don't
recall the spacing of the holes but I would make a guess of 1 diameter
or 0.5 diameter spacing between holes.  I know you can buy the
substrates pre-scored if you want but now you may have registration
problems when doing the thick film.  We were in the process of moving
the laser scoring to the last operation just prior to singulation
because of all the unavoidable breakage and cracking during normal
handling and automated processing.  The trick with the depth of the
laser scoring is that if the holes are not deep enough, the units don't
break correctly and if they are too deep, the units break too easy and
can fall apart during normal forces such as pick-n-place, screen
printing, etc.
        Regarding reflow, this was easy compared to FR4.  The ceramic
distributes the heat more evenly.  Your zone settings can probably stay
pretty much the same but you may need to slow things down to provide
time to stabalize the temp across the board.  I had 12 zones ovens so I
was a bit 'spoiled', but we needed this for 12 second cycle times.

Regards,

Wade Oberle
[log in to unmask]

        -----Original Message-----
        From:   <Charles Barker> [SMTP:[log in to unmask]]
        Sent:   Tuesday, February 02, 1999 5:33 PM
        To:     [log in to unmask]
        Subject:        [TN] Ceramic Boards

        We are faced with creating a "hybrid" made with an ASIC on one
side and a
        custon Ceramic device (abt 0.50" square) on the opposite side.
The ASIC
        will be mounted up-side down to the ceramic "interboard." The
"hybrid" will
        then be attached to an FR-4 board in the conventional manner.

        We will be building these in panel form. The ceramic between the
two parts
        after de-paneling will be .040" thick, and about .6" by .6"
square.  There
        will be .25" spacing between rows of parts. Each panel will be
about 4"
        square.

        I am lookig for suggestions in a couple of areas:
        1. What is the best way of "scoring" the ceramic so things don't
get broken
        and people don't get hurt when snapping the panels apart.
        2. What would be the suggested elevation of temperatures in a
seven-zone
        oven to compensate for the ceramic as compared to an FR-4 board?

        TIA for any input.

        Charlie B.

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