16 Processing and Reliability of Solder Interconnections …
501
with location on the PWA. In other words, the failure mode of PoP components, and
likely also PoPoP components, is very sensitive to the orientation and magnitude of
the shock load, per se.
Clearly, the complexity of stacked package structures and associated interconnections make it difficult to assign general precepts or guidelines to predict the reliability
of the solder joints as a function of mechanical shock. Computational modeling can
take into account the constitutive properties of the PoP and PoPoP materials sets
and solder alloys as well as the geometric configuration of the PWA and shock load
properties. Modeling provides the optimized approach towards predicting solder joint
reliability when being confronted by such a complicated problem.
16.3.3.2 Temperature Cycling
The attributes of stacked packages have garnered the attention of designers in the
high-reliability systems community. Mechanical shock environments are a concern
in some, but not necessarily a majority, of electronics for those applications. Moreover, many of the methods to mitigate the effects of mechanical shock discussed
above—e.g., encapsulation—already have a long history of use in military and satellite payload programs. However, high-reliability hardware is subjected to considerably wider temperature fluctuations, which places an emphasis on the impact of
temperature cycling on long-term reliability.
Temperature Limits
The span of service temperatures is −40 to 85 °C [24]. Use conditions are somewhat more severe for automotive underhood environments (upper limit of 125 °C).
Accelerated aging temperature minimum and maximum values cited in Ref. [24] are:
• 0, 100 °C
• −25, 100 °C
• −40, 125 °C
• −55, 125 °C
• −55, 100 °C.
The most-often used cycles are [0, 100 °C] and [−55, 125 °C] for high-reliability
electronics. Dwell times at the temperature limits ranges from ten to 30 min and
ramp rates must be less than, or equal to, 20 °C/min to avoid thermal shock effects.
The general precept is that, the wider the temperature range, designated as T,
the greater is the acceleration factor. Thus, fewer cycles are needed to bring about the
failures required for a reliability analysis. However, the complex structures of stacked
packages require that careful consideration be given to the accelerated aging test
temperatures versus the T g of the organic materials—molding compound, die attach,
substrate (usually epoxy), underfill materials, encapsulants, and conformal coatings.
If the temperature cycles in service do not cause any of these materials to pass
501
with location on the PWA. In other words, the failure mode of PoP components, and
likely also PoPoP components, is very sensitive to the orientation and magnitude of
the shock load, per se.
Clearly, the complexity of stacked package structures and associated interconnections make it difficult to assign general precepts or guidelines to predict the reliability
of the solder joints as a function of mechanical shock. Computational modeling can
take into account the constitutive properties of the PoP and PoPoP materials sets
and solder alloys as well as the geometric configuration of the PWA and shock load
properties. Modeling provides the optimized approach towards predicting solder joint
reliability when being confronted by such a complicated problem.
16.3.3.2 Temperature Cycling
The attributes of stacked packages have garnered the attention of designers in the
high-reliability systems community. Mechanical shock environments are a concern
in some, but not necessarily a majority, of electronics for those applications. Moreover, many of the methods to mitigate the effects of mechanical shock discussed
above—e.g., encapsulation—already have a long history of use in military and satellite payload programs. However, high-reliability hardware is subjected to considerably wider temperature fluctuations, which places an emphasis on the impact of
temperature cycling on long-term reliability.
Temperature Limits
The span of service temperatures is −40 to 85 °C [24]. Use conditions are somewhat more severe for automotive underhood environments (upper limit of 125 °C).
Accelerated aging temperature minimum and maximum values cited in Ref. [24] are:
• 0, 100 °C
• −25, 100 °C
• −40, 125 °C
• −55, 125 °C
• −55, 100 °C.
The most-often used cycles are [0, 100 °C] and [−55, 125 °C] for high-reliability
electronics. Dwell times at the temperature limits ranges from ten to 30 min and
ramp rates must be less than, or equal to, 20 °C/min to avoid thermal shock effects.
The general precept is that, the wider the temperature range, designated as T,
the greater is the acceleration factor. Thus, fewer cycles are needed to bring about the
failures required for a reliability analysis. However, the complex structures of stacked
packages require that careful consideration be given to the accelerated aging test
temperatures versus the T g of the organic materials—molding compound, die attach,
substrate (usually epoxy), underfill materials, encapsulants, and conformal coatings.
If the temperature cycles in service do not cause any of these materials to pass