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2020 / 11 / 16

Comparative Study on Mechanical and Thermal Performance of eWLB, M-Series™ and Fan-out Chip Last Packages

Meng-Kai Shih

In recent years, Fan-Out (FO) packages have become widely used in handheld, mobile consumer and internet of things (IoT) devices. FO packaging allows greater I/O density as well as the ability to pack multiple components in the same package compared to conventional wafer level chip scale package (WLCSP). Several types of FO packaging are offered in the market today, for example; embedded wafer level BGA (eWLB), M-Series™ as well as a flip chip based structure referred to as Fan-out Chip-Last Package (FOCLP).

We have investigated the mechanical and thermal performance of these FO packages. Finite element analyses were carried out to examine mechanical performance metrics, including warpage, stress in the extreme low-k (ELK) interconnect and board level solder joint reliability. Thermal simulations were completed to compare the thermal dissipation differences among the FO package types. We also applied the optical profile measurement facility advanced metrology analyzer (aMA) to investigate the correlation between in plane strain and out-of plan warpage of fan-out packages at various environment temperatures. A three-dimensional computational model has been developed to compare mechanical and thermal performance of different fan-out package types.

The aMA measurement results have shown that the warpage quantity of M-Series™ structure is lower than eWLB. Besides, the dimension change of eWLB is higher than M-Series™. The performance of the fan-out packages FE model has been verified by comparing the simulation results for the package in-plan dimension change with those obtained experimentally.

In addition, the numerical simulation results show that:

  • The maximum warpage of all types are less than 25um. FOCLP has higher warpage due to high CTE mismatch between thin coreless substrate and compound. Besides, the M-Series™ has lower warpage quantity because backside coating film help to balance CTE mismatch to reduce warpage.
  • The ELK stress of FOCLP and M-Series™ are similar and lower than other package types. This is the result of the molding compound RDL above the copper pillars acting as a stress buffer.
  • The solder ball with maximum Creep strain energy density (CSED) occurs on the outermost solder joint located on package edge at the
    UBM edge. eWLB and M-Series™ packages have similar CSED, while FOCLP has lowest CSED
    value. This is due to less CTE mismatch between the PCB and the FOCLP package.
  • The different types of fan-out packages have similar thermal performance and, overall, dissipate heat better than WLCSP.

More information can be found in the ECTC article entitled “Comparative Study on Mechanical and Thermal Performance of eWLB, M-Series™ and Fan-out Chip Last Packages“.

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