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January 2007

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Subject:
From:
"Todd, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Todd, Richard
Date:
Fri, 12 Jan 2007 09:22:34 -0500
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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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