A couple more:

ADI Reliability Handbook
http://radhome.gsfc.nasa.gov/radhome/papers/RHA98.pdf

The following is a synopsis of a 1999 MicroChip corp presentation:

"
STRAIN MEASUREMENTS IN A THERMALLY-CYCLED FLIP-CHIP-ON-BOARD SOLDERBALL. Elizabeth 
Drexler , National Institute of Standards and Technology, Materials
Reliability Division, Boulder, CO. 

The mismatch between the coefficients of thermal expansion of the silicon chip and the 
organic substrate has been mitigated through the practice of using underfill in
flip-chip packages. The shear stresses on the solderballs furthest from the neutral 
point appear to be eased by coupling the chip to the substrate with underfill. Yet 
solder
fatigue and package failures still occur. This is particularly true for flip-chips on 
organic substrates that are thermally cycled to low (-55 C) temperatures, as well as 
elevated
temperatures (125 C). In this study we used electron-beam moiré to measure 
displacements and calculate strains in a solderball contained in a flip-chip-on-board 
package. A
pitch of 450 nm was used to allow detailed measurements of the displacements. Images 
were acquired of the solderball during ten thermal cycles of the package between
-55 C and 125 C. U-field and v-field images were collected. Initially elastic 
displacements were observed and measured, and the out-of-plane displacements were more
significant than the shear displacements. Subsequent cycles produced plastic 
deformations in the solderball. The source, magnitude, and progression of these plastic
deformations and the potential for failure will be discussed. 
"


I hope some of this is relevant...

aj

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