Fellow Technetters,

We have a problem with a field failure on a flex circuit we manufacture.
This explanation is going to take a while so please bear with me.

The flex problem area is between two wire bondable gold pads. The wire bond
pads are approx. .008 wide with .006 between the pads. The stack from the
top down is 50-75 microinches of soft gold, 150 microinches electroplated
nickel, .0007 RA copper. .002 kapton, .0005 adhesive, .0005 kapton. After
electroplating,  the edge of the flex circuit where the wire bond pads are
is die cut. We have noticed some slivers coming off from the die cutting
(look like gold). The flex is electrically tested twice before shipment
(test voltage is 250V). The flex then goes for die attach. After die attach
another electrical test is performed. It then goes to the end customer who
assembles it into the final box and does another electrical test. The box is
then purged with nitrogen then sealed. After 5 months in the field (benign
office environment) some channels on the die failed. Maximum voltage in the
field is 190 volts.

Our theory is that one of these slivers somehow propagated over between the
wire bond pads and over time caused the short. And to make matters more
complex when the flex cable assembly was removed from the box it worked. We
have done SEM and EDS and do have some evidence of copper between the pads
but the questions are a) can we grow some kind of whisker in this
environment to cause this short b) why are only able to detect copper (no
nickel or gold) c) anyone ever seen this before.

 

Thanks in advance.

Regards Steve Kelly

 

Steve Kelly

(416) 750-8433 (work)

(416) 750-0016 (fax)

(416) 577-8433 (cell)

 


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------