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January 2007

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dehoyos, Ramon
Date:
Fri, 12 Jan 2007 10:56:26 -0500
Content-Type:
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text/plain (408 lines)
	Something to check, if it was sheared off, there should be scuff
marks on the board. A consistent clean shear is very unlikely. Do not
forget to use high magnification to look for this sign.
	Ramon

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, Michael
Sent: Friday, January 12, 2007 10:32 AM
To: [log in to unmask]
Subject: Re: [TN] SMD Capacitor Shear Strength

Rick: Yes, it definitely can be caused by operator handling or better
worded mishandling. 

Let me add to some of the comments made by others. It usually occurs on
parts located towards the outer edge of the board. Also smaller parts
simply do not have as much soldered surface area as larger parts so the
are more easily knocked off with less force. 

The three primary areas we have seen this problem are at: 

*	The exit end of the reflow and/or wavesolder conveyor. Operators
not paying attention, allow boards to stack up and slide over one
another, shearing off components. To alleviate this we poke oke'd it by
installing a proximity switch and alarm. So if the first board is not
removed before the second board arrives it activates an audio visual
signal.

*	Operators sliding boards into transfer carts with sharp edges or
protrusions. These sharp edges act like a guillotine and break off the
part. We have switched to carts that do not have this style of
construction or we have modified them to eliminate it.

*	Transport totes with vertical dividers. If operators are not
careful in how they load or place the board in the tote they can catch a
part on the edge of the divider and knock it off.  We install a rolled
soft rubber edging over the dividers to minimize the impact.


The best way to find out where it is happening is to work your way
backwards from the end of the process until start seeing missing parts.
Example, look at the end of the reflow for parts on the floor and
surrounding area. Look at were they are loading boards into carts or
totes are there components in the bottom or on the floor, etc.



	
Regards
	
Michael Barmuta
	
Staff Engineer
	
Fluke Corp.
	
Everett WA
	
425-446-6076
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Todd, Richard
Sent: Friday, January 12, 2007 6:46 AM
To: [log in to unmask]
Subject: Re: [TN] SMD Capacitor Shear Strength

Ramon,

 

I couldn't agree more.  I have looked at the solder joint areas.  I do
not see any evidence that the solder joints did not wet properly nor had
voiding.

I am trying to build a case against this being caused by operator
handling.
Something more nefarious is at work.

Regards,

Rick 

Panasonic Automotive Systems

 

            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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