Hidehiko Fujisaki

High-performance flip-chip BGA technology based on thin-core and coreless package substrate

A new organic build-up substrate packaging technology was developed in Fujitsu for high-end servers, where lower V-G impedance on substrate and thermal resistance are realized by applying metallic thermal injection materials. In the present paper, two important accomplishments in assembling process, eliminating voids with metallic thermal injection and controlling substrate flatness on mounting large LSIs, are investigated, and evaluated

Development of CPU Package Embedded with Multilayer Thin Film Capacitor for Stabilization of Power Supply

This paper proposes a method of improving power delivery in a CPU package substrate with multilayer thin film capacitors (TFCs). Because TFC embedded technology can reduce the inductance of power delivery path, it can stabilize the power supply to the CPU. Higher permittivity, thinner layer thickness and wider conductor plane area results in larger capacitance. To further stabilize the power supply, we developed a package structure with an embedded double TFC layer that can double the capacitance. The double TFC embedded package was formed by laminating two TFCs to the top and bottom of the core layers in a build–up substrate. Through verification using test vehicles, it was confirmed that electrical performance was significantly improved with the double TFC. Also, it was demonstrated that the criteria of the capacitance and insulation resistance were satisfied in the product reliability tests.

Development of Large Size CPU Package Structure Using Embedded Thin Film Capacitor Package Substrate

This paper reports on a large-size CPU package for UNIX servers which employs embedded thin film capacitor layers. The substrate of this package has two thin film capacitor layers in the surface of the core layer, which has a capacitance of 25 uF in total. In order to adopt this package substrate, we confirmed the effect of the thin film capacitor layers on the package assembly process. We actually measured mechanical characteristics and the coefficient of thermal expansion (CTE), and confirmed that we can use it like conventional package substrates. This package has passed the preprocessing and subsequent environmental test on JEDEC Level 4, and we think that a high-quality package has been developed this time. Fujitsu adopted a low melting point solder BGA from a previous-generation package. Its composition is Sn-57Bi-1.0Ag. However, this solder has an issue with deformation after a low-temperature reflow profile for the solder ball attachment process on the package. In this work, we were able to find the cause of this phenomenon, and by changing the Ag content from 1.0% to 0.4%, we achieved a complete low-temperature assembly process. In addition, BGA connection reliability was confirmed.