Gaetano P. Messina

Internal Thermal Management of IBM P-Server Large Format Multi-Chip Modules Utilizing Small Gap Technology

The large Multi-Chip Modules (MCM) used in the IBM p-Server computer systems, and their predecessors, have required rather unique cooling solutions and module hardware designs in order to meet the thermal, mechanical and reliability requirements placed on the package. The module internal thermal solution has evolved from a spring-loaded metal contact technology to a thermal compound based design using a novel gap adjustment technology employing a soldered conduction component. This current MCM makes use of a novel technology called Small Gap Technology (SGT). This technique makes it possible to control thermal compound interface thicknesses or gaps to a very tight tolerance from chip-to-chip and module-to-module. Heat flux values that have been handled vary from approximately 20 to 53 W/cm2 depending on the type of chip and the system performance level. Even higher heat fluxes have been projected for next generation products. The hardware and processing techniques employed to manufacture these modules are quite unique. These products are typically on the order of 100mm chip carrier size or 140mm overall module footprint on a side (approximately 90 cm2 of carrier area) and contain 8 chips and numerous discrete devices. The process fixturing and equipment must be able to handle the relatively large thermal mass of the components. The sequence of processing steps must take into account limitations on the material properties of the various module components. This paper will describe the SGT thermal management solution. The hardware and process employed to make the gap adjustments and the thermal interface material used in these high heat flux applications will be discussed. In addition, supporting thermal/mechanical modelling, thermal performance data and reliability data will be presented.Copyright

Hermetic Encapsulation Technique Developed for the IBM Z-Server Multi-Chip Module

The large MCM developed to package the main processor unit used in the IBM z9 Server makes use of a novel sealing design that imparts many desirable characteristics to the module assembly process, performance and reliability. These packages consist of a large ceramic chip carrier encapsulated using a copper cooling cap and a metal sealing ring. The sealing technique not only provides the hermetic environment needed to protect the non-underfilled devices contained within the module, but also allows for easy rework of the assembly. The seal used can withstand the thermally induced stresses and strains driven by the thermal expansion coefficient mismatch between the carrier and the cap. Depending on the system requirements or application, it can do this and reliably maintain the level of hermeticity needed to protect the encapsulated devices over a thousand or more thermal cycles. In addition to this, the seal and module design must compensate for mechanical tolerances of the carrier and devices that affect the assembled condition of the module. In the z-Server module design these considerations, as well as thermal performance factors, are all taken into account. This paper will cover the various aspects of the module design, focusing on the novel application of the hermetic seal employed. The seal will be described and its design parameters will be discussed. Seal, component and module level qualification testing that is performed to insure that the assembly meets the package reliability requirements will be presented.Copyright