My money is also on electrical/mis-application failure, unrelated to your
solder process, since you've already ruled out the obvious process issues.
Maybe this one designer always uses this part in an unsuitable application.
And he carries the same piece of circuitry over from one design to the
next.
We once had a customer who reported field failures of a 35V Tantalum cap on
a 5V line. After much trouble-shooting, we ultimately discovered that the
part was designed in with the wrong polarity. And the lay-out correlated
to the design, so the board showed (+) and (-) incorrectly as well. As a
result every single part placed on that circuit location was in reverse,
but since the part polarity matched the layout polarity we never suspected
reverse voltage as the cause of failure. Until the customer finally
tracked all the way back to the design error. To make matters worse, that
piece of circuitry had been a standard building-block used on many
products. They still have the occasional field failure even today although
the design was corrected many years ago.
I have no knowledge of film cap failure mechanisms, but I am sure that they
have certain weaknesses just like other components. If this designer is
using this part incorrectly in a design that he uses over and over, that
could be a potential explanation why only his part fails. Maybe he uses
different derating guidelines than the other designers and consequently,
his parts see higher stresses. Suggest you get your quality folks and the
design engineer and the Roederstein applications experts in a room
together to see if they can figure it out.
Good luck!
Nancy Reynolds
Phil Nutting <[log in to unmask]>@IPC.ORG> on 10/11/2001 12:53:40
PM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: Re: [TN] failing capacitors
I'm not sure if this is an electrically induced failure. I can tell you
that when the cap is replaced the system works well and the cap no
longer shows signs of failing.
An interesting thought... used in an application it cannot support. I
don't have the answer to this one or the knowledge to analyze the
design.
Well, the EE specified what parts to use and the board layout designer
placed the components with the approval of the EE. So I guess they are
both at "fault".
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Thursday, October 11, 2001 10:09 AM
To: [log in to unmask]
Subject: Re: [TN] failing capacitors
Are we sure that this is not an electrically induced failure? Is the
component serviing in an application that it cannot support? By designer
are
we talking EE or board layout designer?
Guy Ramsey
Senior Lab Technician / Instructor
E-Mail: [log in to unmask] <mailto:[log in to unmask]>
Ph: (610) 362-1200 x107
Fax: (610) 362-1290
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Phil Nutting
Sent: Thursday, October 11, 2001 10:17 AM
To: [log in to unmask]
Subject: [TN] failing capacitors
Here is an interesting question.
We use Roederstein film capacitors (through hole configuration) in many
of our boards. Typically all boards are run through our wave solder
machine with the same recipe. The weird thing is that some of these
caps fail either open or shorted but only on the boards belonging to one
design engineer. Is this "full moon residue", a circuit design issue or
is it possible a regular failure that no one else is complaining about?
We keep track of our test failures and if this were happening on many
other boards we should be seeing the data, but there is none.
I'm interested in what your thoughts may be.
Thanks in advance.
Phil Nutting
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