Source: Gabriela Bogdan/SANMINA-SCI (Tel Aviv)
Date: May 2003
This story and images
were offered for posting to
the NASA Tin and Other Metal Whisker www site. The field failure
experience was documented in May 2003. It
describes electrical failures within an RF electronics assembly where
TIN WHISKERS growing from the matte tin-plated RF enclosure (package lid) became
dislodged. As loose debris, the whiskers were able to create short
circuits across exposed conductors (components) within this
enclosure. Click on the Images Below to Enlarge and Read
About This Experience as Told by the RF Assembly Manufacturer
"Dear NASA Whisker Investigators:
When we ordered fences and covers for a RF assembly, our
customer specified matte tin, and hoped for the best. We had
a supplier in Taiwan and one at home. I don't remember how things
developed, but surely not in the right direction. A week ago, our customer brought us failed assemblies
which returned from - anonymous location - after working ~ 1 year. They were puzzled by the
following:
One of the fine pitch components showed electrical
failure
When the lid was opened, and the component changed with a
new one, everything was OK. Then, one smart guy-luckily for me-thought
about resoldering the old component, and again-everything was OK. Now they
come to us and say-
"Your solder joints are bad, see, the same one
turned ok after resoldering. Try to find bad solder joints on those two which
are dead too."
Now, I know these guys, and know that they did not perform
any other tests, and are pretty sure that they can blame the solder
joints. I took the assembly to the microscope and looked at the solder
joints of the component-good shiny ones. Then I tried to find cracks. You
know how hard it is to find them, and I used maximum magnification, turned
the assembly around, focused on each joint- and then I had a call. When I returned to the microscope and tried to focus
again, I suddenly saw "things" all over the place,
and they were metallic, and they were not a result of our process.
Whiskers galore!
Not from the components, not attached to
them, but just laying across everything. Remember the fences and lids?
The fences are reflowed around the area during assembly.
The lid is attached over the fences by the customer after receiving the
assembly from us. Whiskers fell from the lid all over the place in the
enclosure.
But what to do now?
SCARY!!!! Assemblies are returned now. Today I checked 2 years old fences under the microscope. SCHWARZWALD!
("Black Forest") Please look at the pictures. You will enjoy them."
