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JWBK119-15
232 Development of A Moisture Soak Model For Surface Mounted Devices
0.1
Residual 0.0
−0.1
−0.2
−8 −7 −6
(a) Fitted Value
0.1
Residual 0.0
−0.1
−0.2
10 20 30 40 50 60 70 80 90
(b) Observation Order
Figure 15.4 Residuals plots against (a) fitted values; (b) observation order.
current model is adequate for the experimental regime, (30--85 C and 60--85 % RH)
◦
under consideration.
15.3.4 Calculation of equivalent moisture soak time
Combining equations (15.10) and (15.12), we can express the location parameter of
the family of loglogistic distributions as
W t − W 0 RH
a = ln(t) − 2.564 ln = 125.64 + 0.0774 · P − 12.82 − 17.49 ln(T).
W 0 T
(15.13)
From (15.13), the estimate for the common scale parameter, b, for the family of loglo-
gistic distributions is 2.564 (= 1/0.39 from (15.12); see also (15.10) and (15.2)). The
location parameters and their respective standard errors under various experimental
conditions are given in Table 15.5. Using the same principle as in accelerated testing,
the acceleration factor between two testing conditions can be computed by taking the
