16 Processing and Reliability of Solder Interconnections …
475
of the solder joints can be entirely different between the first-level and second-level
interconnections due to the different material sets and structural definitions.
The solder joint arrays will often differ between the first-level and second-level
interconnections. The first-level joints are typically arranged in perimeter arrays (two
rows) around the package perimeters. The second-level solder joints are patterned as
perimeter array (three or four rows) or full arrays on the bottom package. The added
capacity is required of the second-level joints since all of the signals, ground, and
power are routed to the PCB through these interconnections.
16.1.3 Applications Drive PoP and PoPoP Component
Requirements
The performance and reliability requirements that are placed on PoP and PoPoP are
determined by the application. Applications have been categorized by two product
regimes: consumer electronics and high-reliability electronics. Consumer electronics
includes hand-held devices (smart phones, laptops, tablets, etc.) as well as desktop
computers, digital storage media, and entertainment systems. The high-reliability
sector has products such as automotive electronics, telecommunications, high-end
servers, avionics as well as military, space, and satellite electronics. In the case
of consumer electronics, short product cycles and relatively benign use environments (generally offices and homes) allow performance and cost to drive the requirements placed on stacked packaging technology. The primary reliability concern is
mechanical shock caused by dropping hand-held devices to the ground.
High-reliability applications have different requirements for electronic packaging
and associated interconnections. Shock conditions are not unlike those of dropped
personal electronics—some hostile environments can have higher magnitude shocks.
Vibrations have longer durations such as experienced in launch cycles or the constant
flow of forced air in a cooling system. The particular concern posed by vibration loads
vis-à-vis PoP and PoPoP components is not so much degradation to the individual
packages or first-level interconnections between them. Rather, vibration-induced
flexure of the PWA exposes the second-level solder joints to high-cycle fatigue that
can lead to the latters’ failure.
Another concern in high reliability applications is temperature cycling. Aside from
potential thermal degradation of materials at the elevated temperature portion of the
cycle, there is the concern for low-cycle fatigue damage to the solder joints caused the
mismatch of coefficients of thermal expansion (CTE) between the various materials
that comprise the packages, the solder, and the PCB. The degradation scenario is
referred to as thermal mechanical fatigue (TMF), which can lead to a cracked solder
joint and thus, an electrical open.
The TMF condition presents a particularly complex problem for PoP and PoPoP
due to the multiple materials and structures comprising these components. Besides
the molding compound and substrate (interposer) of each individual package, there
475
of the solder joints can be entirely different between the first-level and second-level
interconnections due to the different material sets and structural definitions.
The solder joint arrays will often differ between the first-level and second-level
interconnections. The first-level joints are typically arranged in perimeter arrays (two
rows) around the package perimeters. The second-level solder joints are patterned as
perimeter array (three or four rows) or full arrays on the bottom package. The added
capacity is required of the second-level joints since all of the signals, ground, and
power are routed to the PCB through these interconnections.
16.1.3 Applications Drive PoP and PoPoP Component
Requirements
The performance and reliability requirements that are placed on PoP and PoPoP are
determined by the application. Applications have been categorized by two product
regimes: consumer electronics and high-reliability electronics. Consumer electronics
includes hand-held devices (smart phones, laptops, tablets, etc.) as well as desktop
computers, digital storage media, and entertainment systems. The high-reliability
sector has products such as automotive electronics, telecommunications, high-end
servers, avionics as well as military, space, and satellite electronics. In the case
of consumer electronics, short product cycles and relatively benign use environments (generally offices and homes) allow performance and cost to drive the requirements placed on stacked packaging technology. The primary reliability concern is
mechanical shock caused by dropping hand-held devices to the ground.
High-reliability applications have different requirements for electronic packaging
and associated interconnections. Shock conditions are not unlike those of dropped
personal electronics—some hostile environments can have higher magnitude shocks.
Vibrations have longer durations such as experienced in launch cycles or the constant
flow of forced air in a cooling system. The particular concern posed by vibration loads
vis-à-vis PoP and PoPoP components is not so much degradation to the individual
packages or first-level interconnections between them. Rather, vibration-induced
flexure of the PWA exposes the second-level solder joints to high-cycle fatigue that
can lead to the latters’ failure.
Another concern in high reliability applications is temperature cycling. Aside from
potential thermal degradation of materials at the elevated temperature portion of the
cycle, there is the concern for low-cycle fatigue damage to the solder joints caused the
mismatch of coefficients of thermal expansion (CTE) between the various materials
that comprise the packages, the solder, and the PCB. The degradation scenario is
referred to as thermal mechanical fatigue (TMF), which can lead to a cracked solder
joint and thus, an electrical open.
The TMF condition presents a particularly complex problem for PoP and PoPoP
due to the multiple materials and structures comprising these components. Besides
the molding compound and substrate (interposer) of each individual package, there