I don't think damage is caused by this trait. When profiling causes
unequal solder joints there is a higher rate of failure due to other
traits. Parallel components seem to have more unequal solder joints than
perpendicular. I don't force this issue in my design criteria and good
profiling should keep this to a minimum.
> ----------
> From: Hanamann, Peter[SMTP:[log in to unmask]]
> Sent: Tuesday, September 22, 1998 1:19 PM
> To: 'DesignerCouncil E-Mail Forum.'; 'Kimmey, Frank'
> Subject: RE: [DC] SMD Capacitors Cracking
>
> Frank,
> Could you elaborate a little more on item 2: orientation of
> components? What kind of forces would be causing damage?
> Thanks,
> Peter
> -----Original Message-----
> From: Kimmey, Frank [SMTP:[log in to unmask]]
> Sent: Tuesday, September 22, 1998 10:54 AM
> To: [log in to unmask]
> Subject: Re: [DC] SMD Capacitors Cracking
> Hi John,
> We too had the 1206 cap problem.
> Ours was a .33uF, 50V, Z5U
> We found many attributes causing failure.
> List is not in order of occurrence:
> 1. position of cap on PCB (close to edge)
> PCB flex from depanelization caused micro-cracks (some showing at
> test, mostly field failures)
> 2. orientation of components (we found stress when parallel to
> direction
> of flow)
> 3. Vendor compatability (we found some vendors parts to be borderline)
>
> 4. Profile (temperature ramp-up and cool-down can significantly
> effect)
> Also you may want to research John Maxwell's articles on cap
> failures.
> Please feel free to call me and we can discuss further.
> Hope this helped!
> FNK
>
>
> Frank N Kimmey C.I.D.
> EM Designer
> C&K Systems, Inc
> 916-353-5366
> [log in to unmask]
> > ----------
> > From: John Olivier[SMTP:[log in to unmask]]
> > Reply To: DesignerCouncil E-Mail Forum.;John Olivier
> > Sent: Tuesday, September 22, 1998 7:40 AM
> > To: [log in to unmask]
> > Subject: [DC] SMD Capacitors Cracking
> >
> > I was very interested to see that there are a number of people who
> > have
> > the same problem as we are experiencing regarding SMD capacitors.
> >
> > We have found a number of our 100 NF 50 Volt ceramic de-coupling
> > capacitors are going short circuit after 9 months or more. The
> > capacitors are not a dead short, but are pulling down the VCC line.
> >
> > We are using Kemet X7R 1206 caps. The caps are connected VCC to
> > Ground.
> > Once the cap or caps have been replaced the units work.
> >
> > The printed circuit board is FR4 and is 1.6 mm x 15 cm x 6 cm. The
> > boards go through 2 soldering stages ie. one for the SMD components
> > and
> > then for the conventional components.
> >
> > The printed circuit board once completed is coated with a urethane
> > MS472N conformal coating.
> >
> > I would appreciate any information or suggestions you could offer.
> >
> >
> > Thanks Very Much
> >
> > John Olivier
> >
> > Quality Assurance Manager
> >
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