510
P. Vianco and M. Neilsen
Fig. 16.16 Weibull plots show the thermal cycling results (−55/125 °C; 10 min hold times; and
6–8 °C/min ramp rates) of PoP components, which were covered with a conformal coating and
having either 100% SAC305 second-level solder joints (open magenta symbols) or mixed SnPb/SAC305 bottom joints (open blue symbols). The first-level interconnections were all SAC305
alloy. The corresponding baseline data are also presented, which are assemblies without the
conformal coating: 100% SAC305 bottom joints, closed red symbols and mixed Sn–Pb/SAC305
bottom interconnections, black closed symbols
Temperature Cycling—Effect of Underfill
The effect of adding the underfill material on the TMF of PoP components is
illustrated in Fig. 16.17. Here, both first- and second-level solder joints were SAC305.
The Weibull parameters are listed, below:
100% SAC305: η = 2030 ± 90 cycles; β = 7.1 ± 1.4
No underfill
100% SAC305: η = 2390 ± 210 cycles; β = 4.0 ± 1.0
Underfill, bottom gap
100% SAC305: η = 1680 ± 170 cycles; β = 3.5 ± 0.8
Underfill, bottom and top gaps
When underfill was placed in the bottom gap, only, the higher characteristic
lifetime was accompanied by a decrease of β due to failures occurring earlier in the
cycle count. When underfill was placed in both gaps, a further decrease of β occurred,
which was accompanied by a smaller characteristic lifetime value (η). Therefore, the
use of an underfill to mitigate solder joint degradation due to mechanical shock is
P. Vianco and M. Neilsen
Fig. 16.16 Weibull plots show the thermal cycling results (−55/125 °C; 10 min hold times; and
6–8 °C/min ramp rates) of PoP components, which were covered with a conformal coating and
having either 100% SAC305 second-level solder joints (open magenta symbols) or mixed SnPb/SAC305 bottom joints (open blue symbols). The first-level interconnections were all SAC305
alloy. The corresponding baseline data are also presented, which are assemblies without the
conformal coating: 100% SAC305 bottom joints, closed red symbols and mixed Sn–Pb/SAC305
bottom interconnections, black closed symbols
Temperature Cycling—Effect of Underfill
The effect of adding the underfill material on the TMF of PoP components is
illustrated in Fig. 16.17. Here, both first- and second-level solder joints were SAC305.
The Weibull parameters are listed, below:
100% SAC305: η = 2030 ± 90 cycles; β = 7.1 ± 1.4
No underfill
100% SAC305: η = 2390 ± 210 cycles; β = 4.0 ± 1.0
Underfill, bottom gap
100% SAC305: η = 1680 ± 170 cycles; β = 3.5 ± 0.8
Underfill, bottom and top gaps
When underfill was placed in the bottom gap, only, the higher characteristic
lifetime was accompanied by a decrease of β due to failures occurring earlier in the
cycle count. When underfill was placed in both gaps, a further decrease of β occurred,
which was accompanied by a smaller characteristic lifetime value (η). Therefore, the
use of an underfill to mitigate solder joint degradation due to mechanical shock is