508
P. Vianco and M. Neilsen
Fig. 16.15 Optical
micrographs shown the
microstructural changes to
non-homogeneous, mixed
Sn–Pb/SAC305,
second-level (bottom) solder
joints of PoPoP packages as
a function of thermal cycles
(−55/125 °C; 10 min hold
times; and 6–8 °C/min ramp
rates): (a) as-fabricated;
(b) 600 cycles; (c) 2500
cycles; and (d) 5000 cycles
data, which were obtained from the accelerated aging tests of PoP components
confirmed that the “pooled” conformal coating did not affect the TMF of the
interconnections. The graph in Fig. 16.16 shows the Weibull plots for PoP packages,
which were covered with a conformal coating and having either 100% SAC305
second-level solder joints (open magenta symbols) or mixed Sn–Pb/SAC305 bottom
joints (open blue symbols). The first-level interconnections were all SAC305 alloy.
The corresponding baseline data are also presented, which represented the assemblies
without the conformal coating: 100% SAC305 bottom joints, closed red symbols
and mixed Sn–Pb/SAC305 interconnections, black closed symbols. The graphs
confirmed that the conformal coating had a negligible effect on the characteristic
lifetimes of the PoP solder joints. The corresponding Weibull parameters are listed,
below:
100% SAC305: η = 2090 ± 70 cycles; β = 12.0 ± 3.3
Conformal coating