| May 17, 2012
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Circulation Over 51,000
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| February 22, 2012 |
| IPC-A-610 Criteria |
How did the Class 3 pass/fail criteria in IPC-A-610 come about? Was there field testing and or life cycle testing to support these requirements? If our products need to meet Class 3, but the heel fillets on one gull wing component do not comply with Class 3, but do meet Class 2, and if we do not rework the components, can we meet Class 3 if we conduct additional testing and the product passes the tests? What tests would we need to conduct?
B.P.
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The criteria
for all of the IPC standards are gathered from all over the industry. The data
comes from extensive testing and years of practical experience.
To your
question of, "can we meet class three criteria through testing?" the short
answer is, "No". In order for an assembly to "meet the criteria of the
IPC-A-610" it must do just that; have observable conditions that falls within
the scope of the stated criteria.
Now that's not
to say your customer can't take exception to the criteria. In the opening pages
of the IPC-A-610 you'll find the order of precedence. At the top of the order
of precedence is the customer requirements (contract). If the customer contract
says that the assembly must be built in accordance with the IPC-A-610 criteria,
then that is what you need to follow, no exceptions. If the customer states
something along the lines of, "… built in accordance with IPC-A-610 unless
testing can prove the reliability of the assembly", then you have room for
testing.
If you customer
allows testing for exceptions to the criteria, the customer will have to
specify what tests are allowed.
If you’d like to be
involved in the standards development process, Please join us at one of the
committee meetings held periodically throughout the year. Anyone who uses the
criteria can benefit from knowing where the criteria originates and how the
standards are developed. Check out http://www.ipc.org/Committeepage.aspx
for a list of all the IPC committees and the documents they develop.
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Kris Roberson
Manager of Assembly Technology
IPC
Kris Roberson has experience as a machine operator, machine and engineering technician and process engineer for companies including Motorola, and US Robotics. Kris is certified as an Master Instructor in IPC7711 / 7721, IPC A-610D and IPC J-STD 001D.
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The heel fillet requirement has its history in MIL-STD-2000 and
previous versions of military and NASA standards and has been verified by test.
Unfortunately, those tests were done so long ago finding the data is probably
impossible.
The heel fillet is accepted as the important part of the
connection’s strength, so there is some concern depending on the expected
operating environment. Thermal excursions and mechanical stimuli
(vibration/shock) will stress the connection more than if the hardware resides
in a benign environment.
Additional testing
can be a way to reach a "comfort factor", but you must keep in mind that the
additional testing can also shorten the life of the connection.
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Garry McGuire
Sr. Engineer
NASA/Marshall Space Flight Center
Garry McGuire is a manufacturing process engineer and Chair of the IPC J-STD-001 and IPC/WHMA A-620 Space Addendum committees.
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This response to this
question could take forever; however, let me try to answer it this way.
The plated through hole and
wire wrap sections are based upon historical and best manufacturing practices
which have been in place for the last 50 years. Although the base laminate
materials have changed over the years along with the introduction of lead-free
material some changes had to be made to the manufacturing processes. Those
lead-free changes were incorporated after many tests were designed and round
robin tests were conducted by member companies of IPC. Those results were
submitted to the various task group membership committees, reviewed, expanded
and finally accepted and incorporated into the documents.
As for the surface mount
section which was introduced in the 80’s in revision A, all those examples were
submitted with the appropriate test results defining their goodness and
reliability. The Class 3 customers and users were part of this acceptance
process and if the back up information was not sufficient to satisfy their
requirements, additional testing was conducted to prove the technology. All of
this was conducted along with the reliability people and reliability task
groups who supported the various specifications.
It must be kept in mind the
total quantity of solder joints created during the period of time where this
document was created. The major companies contributing to the original document
were companies like Bell Labs, IBM, Motorola, Martin Marietta, Northrup
Grumman, Lockheed Martin, Hughes, JPL, NASA, Digital Equipment, Raytheon,
Harris, Collins Radio, Rockwell, Texas Instrument, Tektronix, Boeing, AT&T,
Northern Telecom, General Electric, Westinghouse, Magnavox, Honeywell, Trace
Labs, Litton Guidance, E.I Dupont, Sanders Associates, Singer, Naval Avionics,
Canadian Marconi, Nelco, Enthone, Unisys, Sandia Lags, SCI, Pace, Hexacon,
Lawrence Livermore Labs, Computing Devices,
plus many more. The number of solder joints created and the technology
provided by these companies, has been the baseline for the 610 specifications.
So the bottom line is, the
work was done to prove the point of reliability and goodness.
Now
to answer the question as to what happens when one lead does not have the
fillet height to meet the requirement of class 3 which is a heel fillet which
is equal to thickness of the lead. Is this lead reworked or is it dispositioned
to use as is? This can only be answered by the customer who has the knowledge
of where the product is going to be used and the environment where the product
will be used. Would I generate a test to check it out would depend upon how
much money do you have. We can tests these solder joints to failure and still
not know how they will survive in their operational life. My recommendations
would be to check the manufacturing process, measure the amount of solder paste
applied to those locations, define the solderability of the components, and if
these things are acceptable then I would use the component as is with some
ongoing monitoring.
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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
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