Electromagnetic Radiation Study of Intel Dual Die CPU with Heatsink Boyuan ZhuˈJunwei Luˈand Erping Li Griffith University, Brisbane, QLD 4111, Australia Electromagnetics and Electronics Division, Institute of High Performance Computing, Singapore 689048
[email protected] [email protected] [email protected] Abstract — This paper presents an advanced electromagnetic study of Intel Pentium Dual Die CPU. Leading beyond the previous work, an improved structure modelled for the novel generation of Intel Pentium Dual Die CPU is extracted which acts as a patch antenna with high radiation frequency. It is also figured as an upgraded structure for the IEEE challenging problem with multi-core processor on the radiative EMI. The model geometry is extracted from the data sheet of real chip with some approximation. With the help of HFSS, modelling and simulation are accomplished by means of FEM in frequency domain.
I. INTRODUCTION The continuing growth of fabrication process brings intensive integration and high working frequency of the integrated circuit. Taking the processor for example, there are billions of transistors integrated in a single die while the frequency goes up to more than 3 Giga Hertz so far. However, as the performance of ICs increasing thus significantly, the electromagnetic effect turns to be much important in the design. Offered by the joint IEEE/EMC Society Technical Committee (TC-9) and Applied Computational Electromagnetic Society (ACEM) [1], some specific standard challenging problems of electromagnetic are provided and widely studied. According to the previous research [2][3][4], a Pentium4 processor (shown in Fig. 1) with heatsink was modelled and simulated on the electromagnetic radiation emission problem which was developed from the conventional CPU and heatsink simulation model presented by the IEEE challenging model 2000-4. A range of working frequency between 1.40GHz and 2.0GHz are implemented with mPGA package of 478-pin.
Fig. 1 (b) Computer model of Intel Pentium4 processor with heatsink [4]
The model structure is shown in Fig. 1. It is modelled as a patch antenna of a little different from the real chip structure. With the Integrated Heat Sink (IHS) and Substrate on the top, a typical patch antenna structure was used underneath. With the model presented, it was found that a significant amount of radiated emission was collected from the heatsink at the resonate frequency of 2.6 GHz which means the heatsink could be predicted as a perfect antenna with a reflection coefficient of -8.3dB. In this paper, an improved structure of the novel Intel Pentium Dual Die CPU is extracted for the electromagnetic study. With modification for the different processor structure, it then could be used as an upgraded structure for the IEEE challenging problem from the multi-core processor of radiative EMI. Modelling and simulation are implemented using full wave simulator HFSS [9] (High Frequency Structure Simulator) with FEM (Finite Element Method) in the frequency domain. II. UPGRADED INTEL DUAL CORE MODELLING So far as the technique develops, the fabrication process is still following Moore’s Law where transistor number doubles every 18 months. However, due to the limitation of materials, the increasing performance meets a big obstacle with one single die. Thus, multi die integration technology is now implemented in the development of processors.
Fig. 1 (a) Configuration of Intel Pentium4 processor [4]
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A. Frequency domain EM modelling In this paper, modelling is mainly based on the full wave frequency domain simulation which is usually faster than time domain simulation and larger meshes could be used for lower
frequencies. Several frequencies could be investigated in a single time domain simulation. However, deciding the correct frequency range is quite important for the simulation results. Computational errors may be introduced if the solution frequency range is mismatched. The main governing equation for FEM is as follow: 1 (1) ( u E ) k02H r E 0 Pr where, k0 is the wave number in free space, μr and r are relative permeability and permittivity in complex form respectively. B. Prototype structure As there are more than one die inside the chip, radiation emission still exists and the traditional model should be updated. Fig. 2 is given a transverse section of the novel Intel Dual Die processor with heatsink, packaging with a Flip-Chip Land Grid Array (FC-LGA6, pins not shown). The die stands upon the substrate with help of die attach material. Sealing is the integrated heat spreader (IHS) covering the dies in order to protect them. Adhered by the thermal interface material (TIM), the heatsink is fully contacting the top of IHS.
Fig. 3 Extracted model for Intel Dual Core processor in HFSS
The structure specification is detailed in TABLE 1 [5]. Fig. 2 Transverse section of novel Intel Dual Die processor
TABLE 1
C. Extracted Model In the previous work, the chip was simply modelled as a patch antenna. Here, the model is more detailed on the chip itself. As illustrated in Fig. 3, the physical model consists of substrate, dies, IHS, heatsink and other adhesive materials. The whole structure is extracted following the released documents, nevertheless, with certain assumptions of some parameters which are classified. Modification and simplification are implemented to reduce the mesh complex which could save simulation time and resources. The bottom surface of the substrate is grounded and two lump ports are subtracted from it to give the internal excitations separately in order to simulate the two dies action inside the chip. Two probes are standing through the substrate and dies acting as the internal connections. How to find the position of feed point is explained in later part.
STRUCTURE SPECIFICATION OF INTEL DUAL CORE PROCESSOR
Name Height of Heatsink (HH) Height of IHS (HI) Height of Dies (HD) Height of Substrate (HS) Depth of TIM Depth of Die attach material Depth of IHS sealant Length of Heatsink (LH) Width of Heatsink (WH) Length of Substrate (LS) Width of Substrate (WS) Length of IHS external (LIe) Width of IHS external (WIe) Length of IHS internal (LIi) Width of IHS internal (WIi)
Min (mm)
37.45 37.45 33.9 33.9
Typical (mm) 37 1.65 1.15 1.25 0.1 0.1 0.1 67.5 67.5 37.5 37.5 34 34 26 26
Max (mm)
37.55 37.55 34.1 34.1
III. SIMULATION AND RESULTS A. Applied Simulation Setup 1) Materials: The assignments of all materials are described in TABLE 2. TABLE 2 MATERIAL ASSIGNMENT OF SIMULATION MODEL
Name Substrate Die IHS Heatsink TIM Die Attach Material IHS Sealant
Materials polyimide silicon aluminum aluminum silicone silver epoxy
Permittivity 3.5 11.9 1 1 1.8 1 1.8
Radiation boundary is applied in the simulation of open problems where the infinite spread radiation waves need to be calculated. The second-order radiation boundary condition is used as follow: j j ( u E ) jk E u ( u E ) ( x E ) ( 3 ) tan
0
tan
k0
tan
tan
tan
k0
tan
tan
tan
where, Etan is the component of the E-field that is tangential to the surface, k0 is the free space phase constant, Z P0H 0 . B. Resonant Frequency The model built is shown as Fig. 5. Solution is setup with sweep frequency between 2GHz and 6GHz. From Fig. 6 to Fig. 9, several resonant frequencies are calculated for the lumped port 1 and 2 respectively.
2) Excitations: There are several types of excitation sources in the HFSS. In this model, in order to observe the scattering parameter in the close structure, two circle lumped ports with impedance of 50 ohm are defined separately to the two individual dies at the bottom of substrate. Connecting each lumped port, there is a copper probe standing through the substrate and die acting as fed line. The position of these probes is extracted from Fig. 4 where the hottest points represent the highest currents flow and activities [6][7][8]. Fig. 5 Simulation model of Intel Dual Core with Heatsink
(1) The resonant frequency at port1 found between 2 and 4GHz is 2.18GHz with S11 value of -20.94dB.
Fig. 4 Dual die hot spot locations [7]
3) Boundaries: Finite conductivity boundary and radiation boundary are applied in the model. As the real substrate is implemented with several layers, we simplified the structure with the bottom applied as the ground with finite conductivity boundary. The radiation boundary is used on the surface of surrounding air. A box shape model is employed instead of sphere for more suitable results. Finite conductivity boundary means imperfect conductor where the following condition applies: (2) Etan Z (ˆ n u H tan ) where, Etan is the component of the E-field that is tangential to the surface. Htan is the component of the H-field that is tangential to the surface. Zs is the surface impedance of the boundary.
Fig. 6 The reflection coefficient S11 sweep between 2 and 4 GHz at port1
(2) The resonant frequency at port1 found between 4 and 6GHz is 5.07GHz with S11 value of -15.31dB.
Fig. 7 The reflection coefficient S11 sweep between 4 and 6 GHz at port1
(3) The resonant frequency at port2 found between 2 and 4GHz is 2.18GHz with S11 value of -6.20dB.
Fig. 11 Radiation patterns (Phi=0, 0̰Theta̰360°) of 2.18GHz (Right) and 4.90GHz (Left) Fig. 8 The reflection coefficient S11 sweep between 2 and 4 GHz at port2
(4) The resonant frequency at port2 found between 4 and 6GHz is 4.90GHz with S11 value of -21.83dB.
IV. CONCLUSIONS In this paper, an upgraded structure of processor model for Intel Dual Die is introduced beyond the previous research work of Pentium4 processor. Comparing with Pentium4 which resonates around 2.6GHz with reflection coefficient of -8.3dB, the dual die processor resonates significantly around 2.18GHz and 4.90GHz with reflection coefficient of -20.94dB and 21.83dB respectively. With two dies inside a single chip, it tells the new structure of novel processor is also acting as an efficient antenna. Further optimization could be progressed in order to reduce the EMI by using optimized heatsink shape and size. REFERENCES
Fig. 9 The reflection coefficient S11 sweep between 4 and 6 GHz at port2
C. Radiated Emission As resonant frequencies found previously, 2.18GHz at port1 and 4.90GHz at port2 are mainly analysed. Fig. 10 illustrates the far-field distribution of these frequencies. The radiation efficiencies are found as 76.25% at 2.18GHz and 84.99% at 4.90GHz which are high enough for an effective antenna.
[1] [2]
[3]
[4]
[5]
[6]
[7]
[8] Fig. 10 The far-field distribution (E field) of Dual Core model at 2.18GHz (Right) and 4.90GHz (Left) with Phi=0
Radiation patterns of 2.18GHz at port1 and 4.90GHz at port2 are shown in Fig. 12.
[9]
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