Solder Joint Crack Initiation and Crack Propagation in a TSOP Using Strain Energy Partitioning
D. Barker, V. Gupta, and K. Cluff
Modern electronic packages are required to function under severe environments
where temperatures can range form ?5ºC to 125ºC. Severe
temperature cycling between power off and power on conditions can lead
to an early failure of solder joints. Many empirical and mathematical
models based on stress, strain, fracture mechanics, strain range partitioning
etc. are available to find the fatigue life. A new strain energy-partitioning
model is used in this paper and is felt to more accurately predict the
response of the solder. The strain energy partitioning model is used
to determine the potential crack initiation sites and then the model is
extended to follow these cracks as they propagate through the solder joint.
A 40 lead, 20 mil pitch TSOP is used as an example application of the method
and the results are favorably compared with experimental data. The
local CTE mismatch between the lead-solder interface and the PWB-solder
interface is found to significantly affect the fatigue life. This
local CTE mismatch has raised reliability concerns that were previously
not considered to be a dominating issue.
article is available to CALCE Consortium Members.