Tom Ellison and John Burke will be discussing related issues at our CPMT
evening meeting March, 2006, Sunnyvale Ramada. Check <www.cpmt.org/scv>
in a few days.
--- Thomas Ellison <[log in to unmask]> wrote:
Harvey,
I think what might be beneficial is a talk about the compliance
challenges for small and medium sized companies. These challenges may
eventually impact the survival of these companies particularly if they
sell to customers in the E.U. Here are some of the challenges when you
get to the practical, implementation level of RoHS:
************************
Product Conversion Issues
There is significant expense in just reviewing every component of every
product for RoHS compliance. It is usually much more involved than just
re-specifying RoHS compliant parts on the AVL. At some point, you may
encounter a component where it is difficult to eliminate the offending
RoHS element (Cd, Pb, etc.) and still make your product work.
Major corporations have been very active in proposing exemptions to the
E.U. Steve Andrews (TAC repr for G.B.) indicated at the last San Jose
IPC/JEDEC Lead Free Conference that the bar would be raised in the
future for these proposals -- much more extensive and compelling data
would be required to get exemption consideration in the future. This
type of research, compilation and lobbying is expensive -- I fear small
companies do not have the resources to get their exemption added to the
list.
***************************
Compliance
Ensuring compliance is difficult when you have hundreds of part numbers
from multiple suppliers, the simplest of which have 5 or more
homogeneous constituent layers. The limits set by the E.U. appear to be
set at such low levels that extensive calibration with standards are
required to make screening with XRF equipment useful. While you can
always send samples from each supplier for each part number to an
outside lab for analysis, this gets expensive very quickly: 100's of P/N
X 4-5 Suppliers X multiple lots = $$$$. If you are a large customer, you
can "order" your suppliers to analyze everything and send you the
results (for free of course). This does not work so well if you are
smaller customer.
Just following the more popularly stated protocols are difficult and
expensive. (CoC from each supplier, audit testing of multiple lots,
documentation of the results, etc.) In addition to the analytical
chemistry involved, one has to set up some type of system for the folks
doing the screening to factor in the several pages of exemptions now in
place. They must know when it is "OK" to have Pb, Cd, Br and when it is
not. For example, Pb in the solder or terminations is "NOT OK" in a
resistor but Pb in the glass passivation of the resistor "IS OK" because
of an exemption for "Lead in glass of electronic components".
Perhaps the untold story in all of this, is what happens when the
samples reach the chemistry lab. For a piece of plastic, it's simple:
cryogrind it (without getting Cr from the stainless steel grinding
blades getting into the sample), take the powder and dissolve it in a
solvent and analyze it with ICP-AES. But how do you deal with a
resistor? Remember, Pb in the terminations is "NOT OK" but Pb in the
passivation oxide layer "IS OK" per Exemption 5 of the Annex of the
Directive. An 0402 resistor weighs perhaps, 0.5 mg in total. Most of
the methods require several grams of sample. Do you grind up a lot of
0402 resistors to get a couple of grams? But when you grind it up, the
Pb you find is a mixture of the good Pb (passivation layer oxide)and the
bad Pb (from the termination)!! Admittedly, I'm focusing attention on a
very small part on an assembly but the law does say 0.1% Pb in any
homogeneous constinuent layer.
What will an E.U. inspector do on August 2006?? Well, the point is,
we're not sure what he/she will do. I have asked this question of many
national RoHS Testing labs and even Steve Andrews (TAC representative
for Britain). So far I have received only answers such as "Hummm, we'll
have to give that further consideration and get back to you".
*******************************
Tin Whiskers
Everyone is rightfully afraid of tin whiskers from 100% tin plated
components. Various mitigation strategies are being advocated. Most
customers are now demanding extensive testing if a Cu/Sn termination is
used. Suppliers have done precious little testing -- at least that they
are willing to share openly. These tests are time consuming, expensive
and, as far as I know to date, don't really prove that a part will be
whisker free. The tests are the best that science has to offer at
present but, once again, multiply these testing requirements for 4-5
suppliers over hundreds of parts and you have a huge expense. Even if
all you try to do is collect and complile test data from each supplier,
the task is large when you have hundreds of part numbers and multiple
suppliers.
One mitigation stategy advocates switching to a nickel barrier between
copper and tin terminations to reduce the likelihood of Tin whiskers.
Over the last year we have seen a number of excellent papers raising
concerns about Kirkendahl voiding when Tin-Nickel interfaces are exposed
to extensive thermal aging. One wonders if we aren't replacing the
devil we know with the devil we don't? Are we really just substituting
"3 point bend" tests and "drop" impact tests for Tin whisker testing
when we request a nickel barrier?
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