16 Processing and Reliability of Solder Interconnections …
493
An important take-away from the cited studies is that it is not always possible to
control warpage by intuition or general, qualitative precepts. Rather, computational
modeling provides a better method to predict warpage because it can take into account
multiple variables—materials properties, geometries, and the process temperature
profile. Then, more limited empirical studies can be used to validate the model
predictions.
Lastly, most of the investigations addressing stacked packages have, as exemplified by even the limited list of citations in the reference section of this article,
considered largely PoP components. Computational modeling, together with validation experiments, will be absolutely necessary to develop assembly processes and
reliability predictions for PoPoP components, especially as individual packages grow
thinner, and the solder interconnections become smaller in size.
16.3 Solder Joint Reliability
This section examines the long-term reliability of solder interconnections associated
with stacked packages. Those interconnections include the first-level solder joints
between the individual packages and the second-level interconnections that attach
the bottom package to the PCB. A description is given of the environments that
affect PoP and PoPoP reliability, followed by a brief synopsis of current empirical
findings. The chapter is rounded out with a look at a reliability study that included
both computational modeling and empirical testing. Those studies have formed the
groundwork to support the implementation of stacked package technology in highreliability applications.
The fact that this chapter places a focus on solder joint reliability should not
be construed to imply that the reliability of the individual package components—
molding compound, wire bonds, die, and substrate (interposer)—are inconsequential or even of a lesser importance, to PoP and PoPoP technology. These structures
are sensitive to different specific conditions—e.g., moisture and corrosive contaminants—that do not necessarily impose a significant risk to the solder interconnections.
The current trend towards increasingly thinner packages implies that the molding
compound provides a reduced barrier to external environments, which may increase
the risk of failure to die attach or wire bond structures.
16.3.1 Environments
16.3.1.1 Use Conditions
The stacked package can be exposed to a considerable range of use conditions. The
discussion, below, will consider two general categories. A further breakdown of use
conditions is described in the current revision of the standard: “Performance Test
493
An important take-away from the cited studies is that it is not always possible to
control warpage by intuition or general, qualitative precepts. Rather, computational
modeling provides a better method to predict warpage because it can take into account
multiple variables—materials properties, geometries, and the process temperature
profile. Then, more limited empirical studies can be used to validate the model
predictions.
Lastly, most of the investigations addressing stacked packages have, as exemplified by even the limited list of citations in the reference section of this article,
considered largely PoP components. Computational modeling, together with validation experiments, will be absolutely necessary to develop assembly processes and
reliability predictions for PoPoP components, especially as individual packages grow
thinner, and the solder interconnections become smaller in size.
16.3 Solder Joint Reliability
This section examines the long-term reliability of solder interconnections associated
with stacked packages. Those interconnections include the first-level solder joints
between the individual packages and the second-level interconnections that attach
the bottom package to the PCB. A description is given of the environments that
affect PoP and PoPoP reliability, followed by a brief synopsis of current empirical
findings. The chapter is rounded out with a look at a reliability study that included
both computational modeling and empirical testing. Those studies have formed the
groundwork to support the implementation of stacked package technology in highreliability applications.
The fact that this chapter places a focus on solder joint reliability should not
be construed to imply that the reliability of the individual package components—
molding compound, wire bonds, die, and substrate (interposer)—are inconsequential or even of a lesser importance, to PoP and PoPoP technology. These structures
are sensitive to different specific conditions—e.g., moisture and corrosive contaminants—that do not necessarily impose a significant risk to the solder interconnections.
The current trend towards increasingly thinner packages implies that the molding
compound provides a reduced barrier to external environments, which may increase
the risk of failure to die attach or wire bond structures.
16.3.1 Environments
16.3.1.1 Use Conditions
The stacked package can be exposed to a considerable range of use conditions. The
discussion, below, will consider two general categories. A further breakdown of use
conditions is described in the current revision of the standard: “Performance Test