Hi Rick:
Take a look at the missing component area on the board.
Look at the solder joint areas. Look for voids or signs of poor wetting.
Make sure that the components have a good metal wettable termination
finish. I suspect that those caps are old and oxidized. A well soldered
cap would not pry off easily when someone is trying to remove it by
force.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Todd, Richard
Sent: Friday, January 12, 2007 9:23 AM
To: [log in to unmask]
Subject: Re: [TN] SMD Capacitor Shear Strength
Hi Werner, Hi John, Hi Steven -
Thank you for your responses.
I regards to the question of "Why?" We are experiencing some capacitors
that are broken off of the PCB; not a lot, just a few. The prevailing
wisdom is that during physical handling of the PCB, an operator is
inadvertently breaking the parts off the board. This suggestion
prompted me to think about the shear (or peel) force required to break
the solder joint of a 0603 capacitor.
My original question was not prompted by a concern for the reliability
of the solder joint, but simply whether or not an operator, under normal
conditions, can exert enough force on a low-profile device to break the
solder bond.
By the way, I failed to mention that our surface finish is HASL.
Regards,
Rick Todd
Senior Engineer
Process Quality Engineering
Panasonic Automotive Systems Company of America
Division of Panasonic Corporation of North America
776 Highway 74 South, Peachtree City, GA 30269
770-515-1087 Direct
678-458-2887 Cell
770-486-2248 Fax
[log in to unmask] <mailto:[log in to unmask]>
_____
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, January 11, 2007 9:37 PM
To: [log in to unmask]; [log in to unmask]
Subject: Re: [TN] SMD Capacitor Shear Strength
Hi Rick, hi John,
I am indeed on line-are not all consultants working 24/7?
Whenever the shear/pull stength question comes up, my first reaction is
'Why?'
Here is my standard answer:
No standards on shear/pull tests exist-nor should they exist. And there
are good reasons none exist.
First, there cannot be such thing as a true 'shear/pull test;' while you
are of course stressing the solder joint, what you are doing to the
solder joint in most cases is primarily peeling it-the proper reference
would be a 'peeling' test.
Second, the solder joint strength, as determined by a lead peeling test,
has no bearing on the reliability of the solder joint, provided the
peeling test does not reveal inadequate wetting or poor metallization,
e.g., 'Black Pad.'
Third, in a peeling test you always need to observe the whole peel-load
history for the whole peeling process; e.g., with a leaded solder joint
the largest load will be at the initial portion of peeling through the
heel fillet, with lower loads subsequently depending on whether or not
(or to what extent) side fillets are present.
Fourth, the fracture surfaces of the peeled solder joints give typically
more information than do the peel-load histories, because the ONLY
really important finding is whether or not adequate wetting has taken
place, i.e.
the separation is mostly in the solder vs. being interfacial; or whether
or not the metallization is the 'weakest' link, i.e. the separation is
between metallization layers. Good quality solder joints frequently
cause failure between the soldering pad and the component/PCB resin
matrix.
Fifth, for leaded solder joints, the reliability in actual use does to a
large extent depend on the heel fillet and the 'bottom flat' wetting; if
the foot length is <3W, than also on the presence of a toe fillet,
because short feet 'rock' during thermal cycling. Side fillets are less
important, unless you have wetting problems.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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