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OTE/SPH
OTE/SPH
August 31, 2006
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JWBK119-15
Moisture Soak Model 233
Table 15.5 Predicted values of location parameter.
Relative Location
◦
Package Temperature C humidity (%) parameter, a SE of a
1 30 60 23.1608 0.0501
1 60 60 21.7372 0.0378
1 85 60 20.6315 0.0481
1 85 85 19.7348 0.0503
0 30 60 23.0834 0.0421
0 60 60 21.6597 0.0263
0 85 60 20.554 0.0398
0 85 85 19.6573 0.0424
−1 30 60 23.0059 0.0501
−1 60 60 21.5822 0.0378
−1 85 60 20.4765 0.0481
−1 85 85 19.5799 0.0503

ratio of their respective times taken in achieving the same weight gain; which, in turn,
can be expressed as the exponent of the difference between the respective location
parameters. For the same package type, the acceleration factor, AF, is given by

17.49

T 2 RH 1 RH 2
AF = exp(a 1 − a 2 ) = exp −12.82 − . (15.14)
T 1 T 1 T 2
From (15.14), the relative acceleration factor for the four testing conditions can be
computed. The results are shown in Table 15.6. It should be noted that the point
estimate of AF is independent of package type; however, the interval estimates are
dependent on package type due to different standard errors (see the last column of
Table 15.5). Given the AF, the equivalent soak time under a higher temperature--RH
combination can be estimated. For example, if a level 3 package is subject to 60/60
soaking condition instead of 30/60, the soak time will be 46.3 hours instead of 192
hours as recommended by the JEDEC -- a reduction by a factor of 4.15.
An approximate confidence interval for the acceleration factor could be obtained
from the confidence interval for a 1 − a 2 using normal approximation. Specifically,
fromTable15.5,thestandarderrorsforthedifferencesbetweenthelocationparameters

Table 15.6 Acceleration factors for the current testing conditions with 95% confidence limits.
Testing conditions in C/%RH
◦
Temp( C)/%RH combination 85/85 85/60 60/60
◦
30/60 (levels 3,4,5,6) 30.75 (26.76,35.34) 12.54 (10.95,14.37) 4.15 (3.67,4.70)
60/60 7.41 (6.55,8.38) 3.02 (2.68,3.41) 1.00
85/60 (level 2) 2.45 (2.14,2.81) 1.00 --
85/85 (level 1) 1.00 -- --