Hi JaMi!
We didn't discuss other product lines...I was just worried about the parts I
was dealing with. These were cracking during assembly, and yes, it just
appears to be just the case (so far). We're not doing any lead-free stuff here,
so the reflow profile is pretty normal. As far as I know, all my profiles
comply with everything that is published about good reflow profiles. I have a
Electrovert Omniflo-10, with 10-zones to work with, so I can do just about
anything I want to do.
The board was finished with ENIG, and double-sided SMT....no wave solder.
That's why you still see the vias shiny...
-Steve Gregory-
Steve,
First, thanks for the heads up.
Did Coil Craft say that the problem extended to any other product lines?
Are the inductors cracking in the assembly process (i.e. due to the heat
encountered
in the soldering and other processes), or are they cracking during actual
use?
Based on the picture, I would say that the cracking appears limited to the
"case" or
shield, but that may not be the case in every instance. Did Coil Craft say
whether
or not the crack in the "case" affected the coils electrical performance or
the
shielding capability?
Notwithstanding Coil Craft's admission of a problem, I would still ask the
following
two questions.
Are you possibly cooking these puppies a little too much during a Lead Free
soldering process with possibly an improper profile?
If they are cracking in use, I would think that an additional engineering
evaluation
would be in order just to make sure that there wasn't too much current being
pumped
thru the inductors which could cause them to heat up far beyond their
intended
design use or anything encountered during the assembly process.
As a side issue, I just couldn't help but notice that the two diodes shown
in the
picture happen to be packaged such that when oriented with the case
positioned so
that the part number text was "right reading" that there are two "polarity
indicators", a notch and a band, obviously both identifying the Cathode, and
that
the "polarity indicators" are on the left. These guys must have been
anticipating
IPC-7351. ;^)
Just out of curiosity, one can not help but notice all of the bright shinny
vias in
the picture, are they unprotected bare copper?
JaMi
----- Original Message -----
From: "Steve Gregory" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 29, 2004 2:04 PM
Subject: [TN] Cracked Cases on SMT Power Inductors from Coil Craft...
> Hi All!
>
> I just discovered a problem with some SMT Coil Craft Power Inductors, it's
their
MSS1260 series. The problem is that the cases are cracking. I don't know if
any of
you have experienced this, or know anything about this issue, so I thought I
would
share what I just learned this afternoon. Take a look at:
>
> http://www.stevezeva.homestead.com/files/CrackedCoil.jpg
>
> We just discovered these on assembled product..naturally :^(
>
> I called Coil Craft and spoke with their Quality representative, and they
said
that they are aware of the issue, and have changed their assembly processes
back on
September 16th to address the issue.
>
> The reason that the coil cases were cracking, was because they were
filling the
entire cavity between the surface of the winding around the coil, and the
inside
surface of the case with potting compound. During subsequent heating, the
expansion
of the potting compound would stress the case and cause it to crack. I was
told that
inductors made after September 16th would only have potting compound in the
> corners to allow for expansion.
>
> So if any of you have any of these sitting around in your stockroom, I
wouldn't
use them without inspecting them to see if the cavity is completely full of
potting
compound.
>
> -Steve Gregory-
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