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July 2001

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Subject:
From:
Dick Thompson/MKT/HQ/KEMET/US <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 23 Jul 2001 14:41:24 -0400
Content-Type:
text/plain
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Hello John,

You should be very careful in this situation if you are speaking of cracked
solder joints on SMT 0805 ceramic chip capacitors.  Flex cracking under the
terminations is generally regarded as one of the primary causes of failure
of ceramic chips.  If you can see cracks in the solder joints from board
flex, those chips are certainly strongly suspect, and there is possible
latent damage to other ceramic chips, where the damage may not be readily
apparent.  When flex stress is present, then cracks may occur under the
capacitor terminations, and may be nearly invisible on the exterior
surface.   As a result, visual sorting cannot be relied upon to remove all
damaged chips.

Such cracks may result in capacitor failure through increased leakage or
short circuits if they intersect opposed electrodes.  Some such damage may
be latent, not readily detectable during your in-house electrical or
environmental testing.

Ceramic chips mounted very near the edges of the board are often the ones
seeing the most mechanical stress.  Most SMT ceramic capacitor suppliers
have recommendations and guidelines with respect to minimizing flex stress.
Primary factors include part location/orientation with respect to the board
edge, depanelization techniques, connector mating, and general board
handling procedures/fixtures.

Regards,

Dick




John Fahey <[log in to unmask]>@IPC.ORG> on 07/23/2001 11:10:06 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to John Fahey <[log in to unmask]>

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:
Subject:  Re: [TN] Inspection Criteria


Kathy, et al,

Thank you for your detailed input. In regards to your first paragraph, I am
actually looking for some good quality photos of cracked solder joints on
capacitors. We are getting some cracks along the solder joint of an 0805
SMT
capacitor, probably due to board flex (these capacitors are located along
the board edge). Do you have any photos you could share with me so I can
show our inspectors what is acceptable/not acceptable.

Anything would be of help, I do not have the capabilities/equipment to take
photos of these defects in house.

Rgds,
John

John Fahey
Manufacturing Engineer
Echelon Corp

415 Oakmead Parkway
Sunnyvale
CA 94085
[log in to unmask]
Phone: 408 938 5330
Fax:     408 328 3804



-----Original Message-----
From: Kathy Kuhlow [mailto:[log in to unmask]]
Sent: Monday, July 23, 2001 6:48 AM
To: [log in to unmask]
Subject: Re: [TN] Inspection Criteria


I prefer to have the inspectors refresh train on the minimum requirements
annually.  I also am always looking for good photo's that I can put out to
the inspection group of minimum acceptable.  The IPC-610 Rev C has some
really good photo's and I back up this with actual photo's.  I make a lot
of
the minimum acceptable photo's and get lots of copies.  I have been doing
this since I first became an IPC-610 C instructor.  I also include these in
my outside training that I do for the local tech colleges.

A couple of things that are in place here are:
1. I double check defects noted by performing secondary inspections
periodically and on all first builds.
2. If a defect is questioned the person making the rejection has to prove
in
the IPC-610 why it is a defect exactly by clause.

I have an inspector that is always looking for the mole hill.  I appreciate
her toughness because the processes before her know that she will be
looking
at everything with a fine tooth comb and they do perform better knowing
that.  I also like the fact that she is so thorough in her inspections and
everything gets questioned.  Luckily she also really understands the
minimum
requirements and applies the criteria correctly. She provides a tremendous
amount of feedback for borderline processes.  This allows us to really
utilize minimum acceptable as a process improvement opportunity.

Kathy

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