Dear Jana,
I've been lurking long
enough. Just have to put my 2 cents in.
What if:
you are not in the commercial market,
and
there are few companies capable of manufacturing your designs,
and
the design specifications are required for the end product, and
it's
a specialty product, so it is not IBM or Cisco volumes, hence your
vendor
pool is small, and
the supplier has not been able to meet the yields they
initially projected
for such designs, and
then on top of all that...it's
flex...
Without regard to the board
type - if you're trying to work with the supplier (DFM/CE - partnership,
etc.), you should sit down with them and determine why the yields are below
expectations. Based on that review there may be several outcomes.
Those outcomes include requests for design changes, supplier process
improvements, and/or an acceptance of the lower yields with a possible price
concession (if you want them to build more). It's essential that one is
aware of industry wide process capabilities (benchmarking) for that
product. There is competition in the low volume/tight tolerance
marketplace as well as the high volume market, and all suppliers do not have
identical capabilities.
A design can only be
tweaked (real word? spelling?) or DFM'd within the
required technology
design limits. If we designed for 100% yield, we could
not build the
products. I think that's real life for many people. We
accept,
and the manufacturer accepts, that the product yield will be greatly
less
than 100%. Okay, that's life with these products.
This is where the Moonman is
coming from with DFM/CE. The design process is iterative. That is,
you work with your supplier, built a prototype, evaluate the results, and make
adjustments. All parties must work to understand the root causes for any
problems. If a design is pushing the capability envelope, concessions
must be made.
So, then we go back to the basic question(s), what
is reasonable to expect
at incoming - a)100% good product in the door, b)
perform an AQL, c) perform
100% inspection, or d)other...?
From a quality perspective,
the answer depends on what the end user finds acceptable. You can expect
100% good product at the door but somebody has to take steps to ensure that it
really is 100% - even 6 sigma quality has a few parts per billion
defective. If you can't accept any defects, sampling inspection is not
acceptable. You must 100% inspect/test the incoming product.
Remember that AQL is the acronym for Acceptable Quality Level - by definition
the acceptable percentage of incoming defective product that is acceptable to
the production floor. Formulas exist to estimate the percentage of
defective product that the manufacturing floor will see given the percent of
defectives shipped from the supplier and the inspection plan used at incoming
inspection.
Perhaps something you've been saying has more impact
than I realize, as I
think about it - contract negotiations. If the
supplier signs up to meet
design/product criteria and doesn't, my options
are:
a)change suppliers,
b)if a is not possible, negotiate incremental
improvements with the goal of
meeting the specifications?
IMO one must do one or the
other (unless the corporation enjoys suffering). The process where one
determines the best practices available is called benchmarking . Once
the best capabilities available are determined, the choices are living
with the status quo, working with the current supplier base to improve
capabilities, or changing suppliers. The caveat is that perfection does
not exist - the lowest absolute purchase price (not total cost of ownership)
and the most capable process do not often reside within the same walls.
When they do, the world beats a path to their door.
At what
point/product type/product complexity does expecting the supplier
to
provide 100% good parts fail or become unreasonable?
As you might surmise from the
previous comments, this is a very complex question with the cost of detecting
defective material and the cost of shipping defective material becoming part
of the answer. This means that the answer is individualized for each
situation.
I hope that these additional
mental morsels provide nourishment for you. (Translated - I hope that
this gives you some food for thought.)
Don Vischulis