A quick summary:
1) Entek does not offer permanent protection for copper. Any surface
coated with Entek will eventually become exposed copper, and will oxidize.
2) Based on the limited studies I recieved, exposed oxidized copper traces
do not appear to perform any differently than exposed solder coated traces,
At least as far as failure data is concerned. Studies used relatively
clean boards.
3) Concerns with the final cleanliness of the boards were made. A salty
potato chip finger print from the final cabinet level assemblier placed on
the backplane as he closed and sealed the cabinet could become the root
cause of a failure in 6 - 18 months.
4) Conclusion: The practice is acceptable when the cleanliness of the
assembly can be assured through out the manufacture, test, delivery, and
installation of the end item.
5) Application: Since the major contamination is likely to be from
handling, areas not easily handled would fare well. An good application
would be around surface mount components where component spacing is
typically much less than finger width. A poor application would be in open
areas within 2" of the board edges where other post-circuit assembly
personnel would be expected to handle the board.
6) Disclaimer: It should be stated that no input from Enthone was recieved.
The thoughts are those of the author, not Raytheon/E-Systems. Although we
plan on going forward with this, you may be witnessing the Genesis of yet
another Printed Circuit horror story, circa 1998.
Thanks to all who responded.
Original posting follows:
Good day!
We are considering using SMOBC (tented vias) and Entek on a press fit
connector backplane. The assembly process will not coat the Entek with
solder or conformal coat. The boards will go into the field with only
Entek as an oxidation barrier for the copper.
The use environment is in a non-temperature controlled external buildings
(shacks), ie ambient temperatures and humidity. Installations are expected
in high humidity and in arid areas, near oceans, in both hot and cold
climates, basically any metro area.
Question: What level of protection could I expect from the Entek in these
environments? Using IPC definitions of Performance Classes (eg
IPC-RB-276), Would yuo use this for class 2 boards?, Class 3?
Are there any success stories, horror stories, or maybe even data?
I would not be upset to receive a phone call from an Enthone Techie on the
subject.
Thanks for your help.
====================================================================
George Franck
PWB Product Assurance Phone (703) 560-5000 x2648
Raytheon E-Systems M/S N408 Fax (703) 280-4613
7700 Arlington Blvd E-Mail: [log in to unmask]
Falls Church Va 22046 E-Mail: [log in to unmask]
====================================================================
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
|
