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TECHNOLOGY TRENDS

Enhancing the quality and reliability of 2.5D IC packages

By Sajay Bhuvanendran Nair Gourikutty, Lin Ji, Ratan Umralkar, Surya Bhattacharya
[A*STAR Institute of Microelectronics]
Xueren Zhang, Kok Keng Chua [Xilinx Asia Pacific]
I n r e c e n t y e a r s , 2 . 5 D mostly done under time zero conditions, character ization testing into the

integrated circuit (2.5D IC)
i.e., without thermal aging. As a result,
modeling, the swell-strain model can
pa ck ag i ng t e ch nolog ie s
by the material shrinkage due to both
failure caused by material degradation
h a v e s e e n s i g n i f i c a n t it is not possible to predict the product successfully predict the stress caused
commercial success. The increasing under thermal aging conditions. This thermal shrinkage and the shrinkage
input/output (I/O) count, I/O density, imposes great challenges for the product that occurs because of thermal aging at
and the large package size needed for reliability performance assessment. the same time.
high-performance and networking With the aim of providing a better With a strong culture of continuous
applications for 2.5D ICs, and for understanding of the thermal aging- improvement, Xilinx ensures that
ensuring quality and long-term reliability induced polymeric material degradation, its products are always compliant to
of 2.5D IC packages, continues to be ne w m at e r i a l c h a r a c t e r i z at i o n the demanding quality and reliability
a focus in terms of manufacturing methodologies and a new modeling needs of the markets they serve. The
operations. To address these concerns, approach were developed. These developed material characterization
A*STA R’s I M E a nd X ili n x have ef for t s we r e i mp or t a nt b e cau se and modeling methodologies have
successfully demonstrated improved Xilinx’s products serve markets with therefore been implemented into the
methodologies for: a) material testing a broad range of quality and reliability reliability assessment study on a 2.5D
and mechanical reliability modeling, and requirements and as such, the products IC package with a TSV interposer as
b) nondestructive fault localization for must be qualified to ensure that they shown in Figure 1. The study focused
2.5D IC packages. have sufficient reliability margin on the underfill material as it is the key
in the most stringent application material to bridge die, interposer and
Material testing and mechanical conditions with the appropriate level substrate, thereby reducing the solder
reliability modeling of quality. The developed material bump stress. Its performance during the
Thanks to the excellent electrical, characterization methodologies are whole life cycle is important to maintain
chemical, and mechanical properties, able to capture the shifts in material the overall package reliability. First of
polymeric materials have been widely thermal-mechanical properties under all, material characterization tests are
applied in large-volume manufacturing thermal aging conditions for modulus, performed on bulk underfill samples.
for advanced packaging. In Yole’s coefficient of thermal expansion (CTE), The underfill material property shifts
report [1], the polymeric materials and the volume shrinkage after high- under different thermal aging conditions
market revenue is predicted to double temperature storage (HTS) testing. are measured and are compared with the
over the next five years. Polymeric Meanwhile, in order to predict the results for time zero samples. It is found
mater ials ca n be fou nd i n ma ny thermal aging-induced package failure that the thermal aging effect on the
integration process steps: redistribution as early as in the design stage, a novel underfill CTE is not significant because
l a y e r ( R DL), bu m p / u n d e r bu m p numerical finite element analysis (FEA) the underfill samples show an only
metallization (UBM), through-silicon approach using a swell-strain model slightly lower CTE after thermal aging.
via (TSV), and assembly levels, as was developed. By incorporating the With respect to the modulus, thermal
well as at the bonding interface. They measurement results from material aging reduces the underfill storage
have shown increasing importance in
manufacturability, performance, and
reliability in advanced electronics
applications because the package
materials strongly affect the product
performance and reliability. Despite the
superior properties, polymeric materials
usually degrade under thermal aging
conditions. Such material degradation
will adversely affect the package
reliability performance. However, in the
past, the material characterization was
Figure 1: Schematic of a 2.5D IC package with a TSV interposer.

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