WOW. 
This brings me back to the days gone by of Ceramic Leadless Chip Carriers, CLCCs.  When they were 16 pin (or terminal or castellation...) they were fine, soldered great. Then they got bigger and heavier, lowered solder joint thickness and we saw failures.  There were neat "stand-offs" to ensure height and even clever dry soldermask stackers to maintain the .003 min solder joint height.  We would bond our components prior to reflow; white was standard epoxy and pink had .004 ceramic balls to ensure that min condition.  Then came the gull wing friendly passives and the issue pretty much went away, came back with BGAs again and again went away.

If your components are displacing the paste and sitting right on the copper check the process.  Maybe some is has a heavy hand on a semi-automatic pick and place.  Also buy a COTS board and look at that, just as a sanity check.  I don't think I answered your question, hopefully rendered some insight.

Thank you for your service and diligence to solid product.  

Boston Brad
  ----- Original Message ----- 
  From: Hart, Dale L CTR USAF AFMC AFRL/RXSA<mailto:[log in to unmask]> 
  To: [log in to unmask]<mailto:[log in to unmask]> 
  Sent: Tuesday, July 20, 2010 9:23 AM
  Subject: [TN] solder joint height




  We have been doing a some analysis of cca's for the Air Force consisting of
  SMT.  The visual inspection of the solder joints looks very good all
  characteristics above the suggest minimum for class 3 of 610.  The solder
  fillets in some instances could be characterized as being robust.  In
  cross-sectional analysis however, the solder joint height of the components
  electrical termination above the land has been perhaps 0.025 mm to the point
  of needing a SEM to look at the land-solder-component lead interface.
  Closer examination in these areas revealed small cracks in the grain
  boundaries.  I used the term grain boundaries because the solder in these
  areas do not resemble the colonies observed in the bulk solder of the
  fillet.  In some of these instances the land is often deformed in the shape
  of the component lead.  

   

  Would these joints although stronger be more susceptible to fatigue or
  overload failure?

  What are the implications if these cca's are encapsulated?

  What suggestions could be offered to the manufacturer?

   

   

  Dale L. Hart

  Universal Technology Corporation (UTC)

  Failure Analysis

  1270 North Fairfield Road

  Dayton, Ohio  45432-2600

  (937) 656-9165

  Fax (937) 656-4600

  Email:  <mailto:[log in to unmask]<mailto:[log in to unmask]>> [log in to unmask]<mailto:[log in to unmask]>

   


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