John S. Corbin

Finite element analysis for solder ball connect (SBC) structural design optimization

Solder Ball Connect (SBC) is a second-level surface mount electronics packaging technology in which ceramic modules containing one or more chips are joined to a circuit card (FR-4) by means of an array of nonhomogeneous solder columns. These columns consist of a high-temperature-melting 90%Pb/lO%Sn solder sphere attached to the module and card with eutectic solder fillets. The solder structures accommodate the bulk of the strain (which is due to the thermal-expansion mismatch between FR-4 and the 9211 ceramic of the modules) generated during power cycling. If the solder structures are not properly designed, the thermal strain can be a source of premature fatigue failure. In this work, finite element analysis is used to characterize the plastic strains that develop in the SBC interconnection during thermal cycling. Since plastic strain is a dominant parameter that influences low-cycle fatigue, it is used as a basis of comparison for various structural alternatives. Designed experiment techniques are used to systematically evaluate the thermal strain sensitivity to structural variables. Results are used to identify an optimally reliable structure that is robust in terms of assembly-process variables.

Land grid array sockets for server applications

The design and performance of land grid array (LGA) sockets are discussed with respect to high-performance server applications. Motivations for the use of this technology are presented, and the specific challenges associated with its application are discussed from a mechanical perspective. A variety of mechanical performance considerations are identified for LGA socket technologies, and a detailed evaluation of competing socket-actuation designs is presented using finite element structural analysis. Some design approaches are shown to suffer from excessive mechanical flexure, which can consume the allowable range of motion of the contact, resulting in excessive contact load variation within the LGA. Statistical considerations for the mechanical deflections and tolerances that contribute to range-of-motion consumption are developed using Monte Carlo techniques, and a parametric study of the mechanical design variables that influence contact load variation within the LGA is presented.

Packaging the IBM eServer z990 central electronic complex

The z990 eServerTM central electronic complex (CEC) houses four multichip-module-based processor units instead of one, as in the previous-generation z900 eServer. The multichip module (MCM) input/output pin density in z990 processor units is more than twice that of the MCMs in z900 processor units. This increase in packaging density and the consequent tripling of the current drawn by the processor units were accommodated by the first-time use of land grid array (LGA) MCM-to-board interconnections in an IBM zSeries® eServer. This was done by using innovative refrigeration cooling of the MCM with air cooling as backup, and by a new mechanical packaging and power distribution scheme. This paper describes the mechanical engineering of the CEC cage, the LGA MCM-to-board interconnection scheme, and the mechanical isolation of the MCM evaporator-heat-sink mass from the LGA contacts. The paper also describes the electrical power and the cooling solutions implemented to meet the more demanding requirements of the denser CEC package.

Development of a 50mm dual Flip Chip Plastic Land Grid Array package for server applications

For many years, the Flip Chip Plastic Ball Grid Array (FC-PBGA) has been the preferred packaging solution for microprocessors and high performance ASICs. IBM has developed a dual chip Flip Chip Plastic Land Grid Array (FC- PLGA) package to support low and mid range server solutions. This organic 50 mm times 50 mm lead reduced package solution uses a 6-4-6 build-up laminate with two large chips consisting of a processor (22 times 16 mm) and a memory cache (15 times 13 mm) in a single piece lid capping solution. In this paper, we will summarize development activities performed in order to achieve a reliable product while dissipating up to 200 Watts mostly from the microprocessor chip. One of the many key issues to overcome was the assurance of good package thermal stability with such large silicon area coverage over the flexible organic chip carrier. Special chip and module test vehicles were designed and fabricated in order to evaluate the mechanical, electrical, and thermal behaviour of the package post assembly and throughout stress testing. The assembly process development activities performed to support the desired application will be discussed in conjunction with mechanical modeling results. In addition, thermal data will be presented showing the positive results obtained as well as good correlation to the thermal and mechanical models.

Modular server frame with robust earthquake retention

Adequate retention of computer systems during earthquake events is important because it can not only prevent human injury and potential system damage, but also ensure system availability by limiting to acceptable levels the transmitted accelerations to critical system components such as hard drives. This paper discusses the design of an IBM frame structure and related hardware, and the retention methods used, to provide a robust mechanical installation in both raised- and nonraised-floor environments, capable of surviving severe seismic events. The development of the frame structure and the retention hardware involves extensive earthquake simulation testing, in which the responses of the system under different earthquake test profiles are recorded and analyzed in both the time and frequency domains. Industry standards such as the Bellcore NEBS GR-63-CORE and IBM internal specifications are reviewed and compared, and the transient responses of competing frame designs subjected to various earthquake profiles are investigated to ensure compliance. Finally, the concept of modular design, in which various frame components are utilized to create a flexible family of frames, is discussed.