Pat,
Are X-outs causing you a problem or are you just looking to minimize the
number shipped?. The simple approach is to not allow X-outs. Unfortunately
depending on the technology level of your boards, that will cost you $. On
simple low tech boards the difference is typically little but on high tech
fine line boards, be prepared to pay.
In real life, shop yields probably run from 80 to 98% depending on the
degree of difficulty. Your best price per board will be as single boards.
Specifying an array will usually cost more because of wasted panel space
(depending on the shop's production panel sizes). Specifying an array with
no X-outs will cost even more because you are asking you shop to scrap the
good boards on a panel with X-outs. The lower the shop's yield, the higher
the 'no X-out' price.
In situations where you must go with a 'no X-out' policy, you need to
insure that the board you are buying fits the daily niche of that supplier.
This will keep your 'no X-out' price increase at a minimum.
If your insertion equipment is smart enough to avoid stuffing X-outs, it
would be my opinion that your best policy would be to allow them (possibly
add a max. percentage on the number shipped in a lot). X-outs can be very
useful as an educational tool. If you should have a supplier quality
concern, reviewing the X-outs
included in the shipment can be very enlightening. It can lead to a better
understanding of your supplier's manufacturing problems as well as
improvements in your board designs.
Norm Dill
----------
From: [log in to unmask]
To: [log in to unmask]
Cc: [log in to unmask]
Subject: Re: X-outs On Multiple Board Arrays
Date: Monday, December 16, 1996 12:37AM
Hello,
There are a couple of ways to look at x-outs. I have seen one
application
where the impact on yield is calculated by using the binomial
probability
distribution. You know the single-image yield and the number of boards
in
the array. From statistics, you can then calculate the overall yield
as a
function of maximum x-outs allowed.
I think this way considerably overstates the yield impact. For
example,
allowing a few x-outs max on a 20-image array where the single-image
yield
is 90% would drop the overall yield to a very low number using
binomial
probability distribution. It is unlikely that would really happen.
At the other extreme, the 20-image array could be treated as one large
board. How many board fabricators figure in the size of the board when
determining yields for pricing?
These are the two extremes; reality is somewhere in between. What's
reasonable depends on the difficulty and volume of the board. For an
array
of 20 images, 5% is only one image, which may be a bit restrictive for
the
fabricator. I personally think the greater of 20% or 1 image is
reasonable
unless there are circumstances that require more restrictive
specifications. As an additional spec, we sometimes specify the max
percent
of the arrays in a shipment that can have any x-outs. For example, on
an
array with five images, we might allow one x-out on 20% of the arrays
in a
shipment (the remainder would have to be 100% good). This is usually
the
spec we give our fabricators and I have not seen price increases
because of
it.
Regards,
Denis Mori, Materials Engineer
Hewlett-Packard Company
Roseville, CA
[log in to unmask]
______________________________ Reply Separator
_________________________________
Subject: X-outs On Multiple Board Arrays
Author: Non-HP-patb
(rosemail.rose.hp.com!relay.hp.com!simon.ipc.org!uunet.uu.net!zytec!owl!patb
) at
HP-Roseville,mimegw3
Date: 12/13/96 1:04 PM
I was wondering what policies others have regarding accepting x-outs on
multiple board arrays. We currently allow 50%, with the intent being we
would use a two up array with one x-out, but don't want to see 10 x-outs on
a 20 up array. We are contemplating going to something different, say 5%
or 1, whichever is greater. Or possibly no x-outs, but I'm concerned about
the cost ramifications of this (cost is a function of yield, right?). I
would appreciate any input from both fabricators and assemblers.
Regards,
Pat Bailey
Zytec Corporation
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