Thermal Management Solutions for Darlington

Semiconductors’ MicroprocessorsScott Hulbert, Robert Kim, Nicholas Montes, Swetha Viswanatha

Introduction

Procedure

Results

Conclusions

References

• The purpose of our study was to identify thermal

management strategies for a semiconductor chip

• In particular we sought strategies to keep the

temperature rise in a chip below 35 °C as it

generates 2W of heat.

• We tested the thermal behavior of the chip and

obtained a thermal coefficient of resistance, α.

• We obtained contact resistance for each heat sink

• We developed a predictive heat transfer model and

analyzed the effects of heat sinks and air flow

velocity on chip temperature for 2W of heat.

• Finally, we used our model to determine the

feasibility of dissipating 10W of heat while meeting

the same temperature requirements.

• Thermal circuit model reasonably reproduces

experimental data within ±5% accuracy.

• The recommended heat sinks can be used to

manage a 2W power dissipation will maintaining

device temperature < 60 °C.

• Scaling the power dissipation to 10W with tested

strategy is not feasible; alternative strategies should

be investigated.Figure 1: Aluminum heat sinks used in lab,

three 5 pin staggered and one 16 pin aligned

[1] ME 495, 2013, ME 495 Lab 2_Lec3,

https://ctools.umich.edu/portal/site/b88d1bc5-2a10-455b-

8c6c-02618cfa137c/ page/c1ffb53e- 7828-4cee-b406-

c6f54e55f2f2 accessed on October 28th, 2013

[2] University of Waterloo Microelectronics Heat Transfer

Laboratory, 1997, Fluid Properties Calculator,

http://www.mhtl.uwaterloo.ca/old/onlinetools/airprop/airprop.ht

ml accessed on October 26th, 2013

[3] Simons, R., 2003, Estimating Parallel Plate-Fin Heat Sink

Thermal Resistance, Electronics Cooling,

http://www.electronics-cooling.com/2003/02/estimating-

parallel-plate-fin-heat-sink-thermal-resistance/ accessed on

Oct 17th, 2013

Recommendations

Predictive Thermal Model

Thermal Management Solutions

for 2W Power Dissipation

Figure 2: Test bench setup for evaluating chip

with heat sinks

Figure 3: The maximum allowable QH to keep Tchip below

60 °C is shown for each heat sink at the tested air velocities.

Data points that are above QH = 2W meet the thermal

management criteria. Error in QH,Max is too small too be seen

on the graph.

• We characterized the chip thermal coefficient of

resistance.

• We mounted a heat sink on the chip and found the

chip temperature using α at various fan speeds.

• We tested three 5 pin (staggered pattern) heat

sinks and one 16 pin (aligned pattern) heat sink

(shown in Fig. 1), we tested four different air flow

velocities for each heat sink in a small wind tunnel

and measured the fin base temperature with the

thermocouple.

• Total thermal resistance would have to be less

than 3.5 °C/W.

• Current heat sink designs incapable of keeping

the chip temperature below 60°C if the power

dissipation were to increase to 10W.

Tchip

Rconvective, fin

T∞

Rconvective, base

Rcontact

qb

Nqf

Complete thermal circuit model for a heat sink

with heat transfer over the base and the fins.

1. Use 16 pin aligned heat sink

QHMax= 2.50 ± 0.02 W

2. Increase the 5 pin heat sink fin

lengths to 27mm

QHMax= 2.00 ± 0.11 W

3. Use heat sink with 6 parallel

plates

QHMax= 2.35 ± 0.12 W

27m

m

8

13

18

23

28

33

0 0.5 1 1.5 2 2.5 3

(Tc

hip

-T∞

)/Q

H(°

C/W

)

V∞ (m/s)

1

2

3

4

Red – Model

Blue – Experimental

Horizontal error =±0.21

Vertical error =±0.75

Figure 4: Relationship between the chip-to-ambient thermal resistance and air flow velocity for each

heat sink, from experimental and from model outputs. We found our model is accurate within ±5%. Feasibility of 10W

Power Dissipation

Silicon chip with

heat sink

Cooling fan run

at 6-12V

1 2 3 4

Base Thickness: 2.7mm

0

0.5

1

1.5

2

2.5

3

3.5

1 1.5 2 2.5

QH,M

ax(W

)

V∞ (m/s)

5 Pin Short

5 Pin Med

5 Pin Long

16 Pin

4 Plate

(theoretical)

Horizontal error bars removed for clarity

Horizontal error = ±0.21

Vertical error = ±0.12

1

2

3

4

7.3

4 m

m

10

.77

mm

14

.15

mm

17

.98

mm

9.2

1 m

m

Heat Sink Average Rcontact (°C/W)

1 2 3 4

6.07±0.62 6.07±0.62 6.70±0.30 4.05±0.51