Dr. Dereje Agonafer Senior Engineer System 390 Division, IBM 522 South Rd., MS P520 Poughkeepsie, NY 12601-5400 Dept. B02, Bldg. 3-3 Poughkeepsie
Technology advances in integrated circuits have resulted in sizeable increases in density of electronic components. As a result, much greater amounts of memory are available for product developers. One major problem which is a by-product of the advances in computing power, is a very large increase in heat load. For example, the heat flux at the chip level on IBM mainframes has increased by over an order of magnitude compared to the early IBM 303X mainframes. The performance of the electronic components is very much related to temperature values in the components. If the maximum temperature exceeds some value (typically 85:f.degree:ef.C), a severe degradation in performance will result. Consequently, heat transfer is playing an ever increasing role in packaging technology.
The presentation will begin with a brief background of cooling challenges in IBM high end systems. This is followed by a presentation on an integrated approach for modeling of thermal problems related to electronic cooling. In particular, the use of an interface program that enables the extraction of mechanical related information (geometry, material property, ..) from a 2D circuit board design resulting in an automatic creation of 3D CATIA(CATIA is a registered trademark of Dassault Systems) solid models is presented. The required CFD model is then constructed in CATIA using a special function key developed in CATIA by Agonafer and Vimba (1991). The rest of the presentation will focus on applications of CFD to electronic packages, and will conclude by highlighting some of the CFD challenges that are of special interest to applied mathematicians.
The first problem is the solution to a system-level benchmark problem in electronics cooling consisting of a box with covers, floppy drive, hard file, power supply, planar, fans, feature cards and Single In-line Memory Modules (SIMM's) is described. The benchmark problem, proposed in an earlier paper (Linton and Agonafer), is solved using an integrated solid model based pre-processor coupled with a commercially available Computational Fluid Dynamics (CFD) package.
The second problem is the computation of the internal resistance of a TCM. A numerical model of an entire TCM module (without resorting to symmetry conditions) is presented. The model includes a 10x10 array of pistons, and a hat. All the chips (10x10) are included in the model by using thermocoupling technique to introduce the interface resistance between the chip and the piston. This presentation is based on a paper by Agonafer and Free at the 1995 IMECE.
The third problem is a conjugate model of 9x9 pinned fin heat sink for both parallel and impinging flow. The conduction problem is solved using a network model, and the convection problem is solved using a Finite Control Volume (FCV) technique. This presentation is based on a paper by Agonafer and Free at the 1995 Euro Therm.
The last problem is a turbulent modeling challenge in electronic cooling applications. Most of the flow regimes in electronic cooling lie in the transitional regime. A number of investigators have used k-e model; unfortunately, the model is best suited for much higher Reynolds numbers. The low-Reynolds number version of the k-e model, employing damping functions on the k and e equations, has been widely used for resolving the low-velocity near-wall region (Patel et.al (1985)). to a high computational time which makes it impractical. In this last section, the use of LVEL (a scheme that requires a knowledge only of the wall distances and the local velocities) is described. The model performs as well as the older Lam-Bremhorst-Yap and 2-layer-k-epsilon models, but is considerably less computationally expensive. The presentation is based on a paper entitled "The LVEL Turbulence Model for Conjugate Heat Transfer at Low Reynolds Numbers" by Agonafer, Gan-Li, and Spalding, to be presented at 1996 ASME Intl Mech Engr Congress and Exposition in Atlanta.The talk will conclude by summarizing some of the challenges in CFD applications in electronic systems which could be of interest to applied mathematicians. The presentation will be based on panels entitled "Current Problems in Computational Modeling" moderated by Agonafer and Wirtz at the 1989 ASME Winter Annual Meeting in San Francisco, "CFD Benchmark Definition for Electronic Packaging" moderated by Agonafer and Fahgri at the 1992 National Heat Transfer Conference in San Diego, and entitled "Future Directions of Commercial CFD Packages with Emphasis on Elec Pkg" to be moderated by Agonafer and Chen at the 1996 ASME Intl Mech Engr Congress and Exposition in Atlanta.