Heat Analysis

Analysis of Heat Dissipation Performance of CVD Diamond Film’s Sink for 3D-

MCM

Kuojun Xie, Changshun Jiang, Haifeng Xu, Lin Zhu

School of Physical Electronics, University of Electronic Science and Technology of China

Chengdu 610054

Email: xkj@https://www.360docs.net/doc/331240925.html,, Tel : 86-28-83202603, 86-28-66839037

Abstract

3D-MCM may play a important role in microelectronics in next century, a key problem must be solved: how to remove internal heat to exterior effectively in practical use .This work describes the use

of CVD-diamond on stacked 3D-MCM thermal management, the symmetry of the model was utilized,

a three dimensional model of only 1/4 section of the model was built and numerical simulation based

on FEA was performed. A comparison was made between the calculated temperature distribution using

CVD-Diamond and that using other materials .

Internally generated heat is removed to the ambient environment through two paths :Internal and external paths; Internal path is that heat conducts from junction regions of chips to outer surfaces of the cases ;external path is that heat is removed from the outer surfaces of the cases to the ambient environment by convection and radiation .Presently, Three measures are taken to deal with heat dissipation problem ---using low thermal resistance substrates, lowering 3D-MCM temperature by air forced convection or liquid coolant, and removing heat to exterior by heat channels .According to heat dissipation requirements, one or several measures are determined.

CVD diamond, with its superior thermal conductivity (1000-1700w/m.k), is an attractive material for electronic packaging, people are interested in use of diamond in thermal management. Sanders et al [1] have demonstrated GaAs MMIC dissipating 30 watts (W) by diamond enhanced plastic package; Boudreaux et al [2] have demonstrated greatly improved thermal management performance by using diamond in conventional integrated circuit packages; David W.peterson et al [3] have investigated edged-cooled diamond-based 3D-MCMS,and so on.

In this work, Improved thermal management performance by using diamond has been investigated, comparison of CVD-Diamond to other materials for thermal management was made. Numerical simulation based on finite element method was performed .A three dimensional thermal model of a kind of stacked 3D-MCM was built with ANSYS to calculate the temperature distribution and power dissipation .

Numerical modeling:

Presently, In 3D-MCM packaging techniques, module structures include three primary types----Active-3D-MCM, Stacked-3D-MCM, Embeded-3D-MCM .In this work, a stacked 3D-MCM was built as shown in fig 1: the cross sectional structure of the model(a) and top view of the model(b). The 3D-MCM concept involves stacked substrates for electrical interconnection, chips attached to substrate, a CVD-Diamond interposed layer was inserted between two substrates, interposed layer and substrates protruded a little, substrate attached to PCB by solder bumps, identical flip-chips (8mm×8mm×0.65mm)attached to substrates in 2×2 array,1w power was input to each chip. Thermal improvement of stacked 3D-MCM was investigated by using CVD-Diamond with high thermal

conductivity.

Fig1 The cross-sectional structure of the model (a) and top view of the model(b)

FEA was used to evaluate the thermal and structural performance of the configuration, the modeling was performed using the FEA software ANSYS. Considering the symmetry, to reduce solution time and required memory space, one-quarter model was simulated .Solder bumps and solder balls were modeled as blocks instead of the actual truncated spherical shapes, adiabatic conditions were assumed on the planes of symmetry, heat transfer coefficients were assigned to all external surfaces, The value was assigned 20W/mm2.K under air free convection, the ambient environment temperature was 25℃,a uniform heat flux was applied on all top layer elements of silicon chips to simulate heat input. Fig 2(a),(b) show one-quarter model and the meshed model respectively, the finite element model contained 48121 elements and 76883 nodes.

0-7803-9449-6/05/$20.00 ?2005 IEEE. 2005 6th International Conference on Electronic Packaging Technology

Thermal conductivity values were assigned to each of material types in the model as shown in table 1[4-8] . Steady state thermal analyses were carried out to determine the temperature distribution on the model. Table 1.

module material

/w/m.K

PCB FR4 8.37,8.37,

0.32

Solder ball 37Pb/63Sn 50 substrate PI 0.2 Interposed-layer CVD-Diamond 1200 Solder bump 5Sn/95Pb

chip Si

80 Thermal grease

Thermal

grease

adhesive adhesive

1.1

Insulation -layer

AlN 170

(a) (b) Fig2. (a) one fourth model of 3D-MCM (b). Finite element mesh of the model

Results and discussions:

Calculated temperature contour pots of the model and

two chips were given in fig 3, reveal uniform temperature

distribution on chips .The maximum temperature was on the

chips, the value is 84.353℃ but not located at the center of

the chip, and close to the center of the model. The major

contribution of the temperature distribution comes from the

effect of heat-coupling of other chips on the substrate. The

minimum temperature was located at the corner of the PCB,

the maximum temperature was below the safe operating

limit of the chip.

（a ）Temperature distribution of the model

(b)Temperature distribution of the up-chip

Fig3. Temperature distribution of one fourth of the model

888888T h e m a x i m u m t e m p e r a t u r e o f t h e c h i p s /C

T h ic k n e s s o f C V D -d ia m o n d la y e r /m m

Fig4. Effect of the thickness of CVD-Diamond layer on the

maximum temperature of the chips

Table 1 shows CVD-Diamond has superior thermal conductivity, the effect of the thickness of CVD-Diamond

interposed-layer on the maximum temperature of the chips

is illustrated in fig 4. When the thickness increased from

1mm to 3mm, the maximum temperature of the chips decreased only by less than 2℃.Although the CVD-Diamond interposed-layer provides for a heat path and greatly improves the junction temperature of the chips, the

role of the thickness of the CVD-Diamond interposed layer

is less significant as we thought. In practical packaging,

packaging volume is taken into account .it can’t offer more

benefits by increasing the thickness.

By using the APDL of ANSYS, Comparison of using

CVD-Diamond interposed-layer as heat conduction layer

for thermal performance improvement to other materials

was made. Calculated results is illustrated in fig 5,the top

curve denotes the case with CVD-Diamond, additional three

curves stand for the cases without CVD-Diamond,it shows

that the maximum temperature of chips was very high

without CVD-Diamond layer, the maximum temperature easily exceeded the operating temperature limits, with CVD-Diamond layer the junction temperature decreased markedly, this proved that CVD-Diamond layer provided a

primary path for the removement of the internal heat to the outer surfaces of the cases.

T h e m a x i m u m t e m p e r a t u r e o f t h e c h i p /C

ow er input /w

Fig5.Effect of power input on the maximum temperature of the

chips

T h e m a x i m u m t e m p e r a t u r e o f t h e c h i p s /C

convection coefficient of case on the tem peratures of chips /w/m m 2

Fig6. Effect of convection coefficient of case on the maximum temperature of the chips

In practice, additional heat sink, air forced cooling

and liquid cooling are used in order to achieve a better

cooling performance. Numerical simulations were carried

out by different heat transfer coefficients assigned to external surfaces instead of simulating actual configurations [9] . Results is shown in fig 6, it indicates that

the maximum junction temperature of the chips decreases

markedly with the rise of heat transfer coefficient values, when heat transfer coefficients values increased from 20

w/mm 2.℃ to 50w/mm 2.℃,the maximum temperature

decreased from 84.353℃ to 61.513℃.so these measures

can enhance the thermal performance effectively.

With generated heat flux increasing, the development of thermal solutions trend from air free cooling to air forced

cooling and liquid cooling technique, even dielectric phase

change cooling technique .Primary disadvantages of utilizing a liquid cooling and air forced cooling system

include the size and cost associated with the bump, heat

exchanger, tube, fan, and so on . Considering size and cost,

advanced cooling solutions are utilized in large-scale and

high performance electronic equip systems, but small portable electronic productions have to take ordinary air cooling .By using high thermal conductivity materials such

as CVD-Diamond, altering packaging structures, improving heat dissipation efficiency it is a feasible approach to improve 3D-MCM thermal performance. Conclusions

This work primarily has investigated use of CVD-Diamond in 3D-MCM thermal management .it was shown that CVD-Diamond with high thermal conductivity can improve 3D-MCM heat dissipation performance effectively, and offer some references to utilize CVD-Diamond in thermal aspects. It may play a important role in the future. References

[1]Sanders,A Lockheed Martin Co. The thermal benefits of

diamond enhanced plastic packages for microwave applications,1998 IEEE MTT-S Digest 1099-1102. [2]P.J. Boudreaux,“Thermal benefits of diamond inserts and

diamond-coated substrates to IC Packages”1991 Digest

of Papers of the Government Microcircuit Application

Conference,V27,DTIC number GOMAC-91-B160081,PP.251-256,1991.

[3]David W.Peterson et al.“Demonstration of a high heat

removal CVD Diamond substrate edge-cooled multichip module”,MCM’94 Proceedings 624-630. [4]B.I. Chandran,M.H. Gordon,W.F. Schmidt, Comparison of CVD diamond to other substrate materials of thermal management,5th InterSociety Conference on Thermal Phenomena in Electronic Systems,1-Therm V,Orlando FL,29 May(1996) 226-232.

[5]Ninghui Zhu,Thermal impact of solder voids in the electronic packing of power devices,Fifteenth IEEE SEMI-THERM TM Symposium(1999) 22-29.

[6]Teoh King Long,Goh Mei Li,Seetharamu K N,et al.A

fresh look at thermal resistance in electronic packages

[A].Proceedings of IEEE 2000 Electronic Packaging

Technology Conference[C].2000.124.

[7]Lall Balwant S,Guenin Bruce M, Molnar Ronald J. Methodology for Thermal Evaluation of Multichip

packages[J].IEEE Trans Comp,Packg Manufa Technol Part A,1995,18(4):758. [8]Moghaddam S Rada M, Shooshtari A, et al, Evaluation

of analytical models for thermal analysis and design of electronic packages[J],Microelectron J,2003,34:223. [9]S.Kitajo,Y.Takeda,et al,“Development of a high

performance air cooled heat sink for multi-chip mokules”,

Eighth IEEE SEMI-THERM TM Symposium 1992 IEEE

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Acknowledgments This paper acknowledge support from NSFC (60371006)

Xie Kuo-jun was born in Hunan province, China, in 1965. He

received the B.Sc. degre e from the Sichuan University, Chengdu in 1987, and the M.Sc. degree from the Sichuan University,

Chengdu, in 1990. He is Associate Professor and Ph.D.

candidature of UESTC. His research activities have been

concerned with the applications of CVD diamond film’s in microwave and millimeter microwave. Jiang ChangShun , male, born in HuNan province,China,

in 1974. He received the B.S.degree in physics from Ji Shou

University in 1997. Since 2003, He has been a graduate

student, specializing in thermal analysis of electronic packaging for M.S. degree in University of Electronic Science and Technology of China.