I understand that themal cycle considerations are well documented and have good predictors of performance.  However, in harsh environments, drop shock and vibration are also failure mechanisms.  These have received relatively little performance prediction.  Seems to me, those factors are still in the "build some prototypes and try them out" stage.  

Any studies of equivalent BGA and LGA components in high stress or combined environments?   The LGAs will have very low solder joint height, but may perform better due to less component mass (weight of solder balls) in vibration and drop.  

Comments?

Denny Fritz










-----Original Message-----
From: Thayer, Wayne - IIW <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, May 20, 2010 4:17 pm
Subject: [TN] Solder joint height


Should there be a spec for minimum solder joint height for leadless components?  
n old paper from Werner (mid 90's, I believe) popped up on the Internet when I 
ueried this, and Werner has a statement in it that joints less than about 50 
icrons thick are basically all intermetallics, but that is not necessarily a 
ad thing since the intermetallics are stronger than the solder (but more 
rittle).
I figured since we often try to get additional height for BGA joints to improve 
eliability, we should be concerned about QFNs and LCCs.
I grabbed a 1.5mil (37 micron) tungsten rod out of our cleanroom (used for 
learing clogged wirebond capillaries)and started seeing if I could get that 
nder my leadless components.  Couldn't get it under any of them, likewise with 
he QFNs.
Checked Technet archives and didn't see an obvious thread, but maybe I didn't 
ave the correct search parameters--if you just enter "height" you get a couple 
f thousand hits.
Wayne Thayer
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