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November 2003

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Subject:
From:
Bruce D Stilmack <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 18 Nov 2003 05:54:08 -0500
Content-Type:
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text/plain (177 lines)
We deal almost exclusively with military applications and have always used
tweezers and irons for SMT rework or hand installation.  In fact, we have a
few CCA's that we install approximately 30 SMT ceramic caps to the bottom
side after wave, all with tweezers or an iron.  I have yet to see a
documented failure of any of these components during initial Test and have
never seen a return for a cracked cap that was not physically damaged  (by
outside forces).  I have seen absolutely no decrease in reliability nor
increase fall out at Test on hand installed surface mount components.

Bruce Stilmack
GDLS-TO Manufacturing Engineer
(850) 574-4773
[log in to unmask]


                                                                                                              
                    "Morse,                                                                                   
                    Carrie"              To:     [log in to unmask]                                              
                    <CMorse@CIRTR        cc:                                                                  
                    ONICS.COM>           Subject:     Re: [TN] Not that our process is out of control or      
                    Sent by:             anything, but --                                                     
                    TechNet                                                                                   
                    <[log in to unmask]                                                                             
                    ORG>                                                                                      
                                                                                                              
                                                                                                              
                    11/17/2003                                                                                
                    04:52 PM                                                                                  
                    Please                                                                                    
                    respond to                                                                                
                    "TechNet                                                                                  
                    E-Mail                                                                                    
                    Forum.";                                                                                  
                    Please                                                                                    
                    respond to                                                                                
                    "Morse,                                                                                   
                    Carrie"                                                                                   
                                                                                                              
                                                                                                              




Eric,
How about Rework techniques for SMT components?
Any recommendations?  (I'm desperate)
Do you use irons or hot air tools?

-----Original Message-----
From: Eric Laroche [mailto:[log in to unmask]]
Sent: Monday, November 17, 2003 4:50 PM
To: [log in to unmask]
Subject: [TN] Not that our process is out of control or anything, but --


It is the preheat it the wave that is controlled (the infamous 2C/sec)
to prevent thermal shock.  Once the chip has achieved a specified temp,
all the materials have expanded equally and after this point the rapid
thermal change of hitting the wave does not affect the chip.  It is the
different expanding properties of the two materials that cause the chip
to crack.  Once they have both expanded to their maximum state, the
temperature curve is irrelevant.

-----Message d'origine-----
De : TechNet [mailto:[log in to unmask]] De la part de Charles Caswell
Envoyé : 17 novembre, 2003 16:46
À : [log in to unmask]
Objet : Re: [TN] Not that our process is out of control or anything, but
--

Our Space customers require us to use hot air to preheat chips before
soldering with an iron. With wave solder the parts go through preheat
and do not see the temp. change as with a soldering iron. We had a
difficult time convincing some customers of this many years ago.

-----Original Message-----
From: Morse, Carrie [mailto:[log in to unmask]]
Sent: Monday, November 17, 2003 2:27 PM
To: [log in to unmask]
Subject: [TN] Not that our process is out of control or anything, but --


Just wondering what would be considered the "Industry Standard" on
rework method (remove and replace, or touch-up) for ceramic chip caps?
We are currently using Metcal Irons or Tweezers and periodically a hot
air tool (hand held wand)

We have a customer asking us to use ONLY the Hot Air Tool.  He feels
that the thermal shock of bringing the cap from room temp to liquidous
causes stresses within the cap which may cause a failure in time.  To
minimize the rapid temp changes the irons introduce, we have been asked
to use the Hot Air Tool only.

I was surprised at this request as we build some boards for this
customer that have ceramic chip caps that get wave soldered.  I can only
imagine the rapid temp changes those caps see.

Any input or feedback concerning this customer's request would be
appreciated.

Thanks,
Carrie

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