Application Tips
Thermoelectric cooler (TEC) is a semiconductor device which is characterized by unique heat pump performance with high efficiency, compactness and durability. The unique ability of TECs to heat and cool, permits them to lower temperature of an object below ambient as well as to stabilize temperature of objects in widely varying ambient conditions.
Here we mention some application tips that can help in optimal use of TECs.
PROPERTIES OF MATERIALS
Proper mounting of TECs requires taking into account properties of materials in target assembly.
- Thermal conductivity is preferably as high as possible to minimize thermal resistance in assembly which generally reduces performance of TECs.
- Coefficient of thermal expansion (TCE) of all materials in connections must be adjusted (to be close to each other) to minimize thermal stress, which can lead to damage of TECs and considerable reduction of TEC lifetime.
- Thermal properties as melting point and temperature stability must be coordinated to provide correct mounting procedures (particularly soldering and adhesive bonding methods) and long operation of TECs.
Some useful properties of commonly used materials regarding above mentioned are listed below.
Materials of TEC
Material |
Density g/cm3 |
CTE x10-61/K |
Thermal Conductivity W/mK |
Specific Heat J/kgK |
Ultimate Strength MPa |
Young's Modulus GPa |
Bismuth Telluride |
7.85 |
12.9 |
1.5 |
188 |
20-40 |
50 |
Ceramics Al2O3 - 100% |
3.9 |
7.2 |
30 |
800 |
150 |
280 |
Ceramics Al2O3 - 96% |
3.75 |
7.0 |
24 |
800 |
150 |
280 |
Ceramics AlN |
3.3 |
4.5 |
170 |
920 |
n/a |
350 |
Ceramics BeO |
3 |
7.0 |
230 |
1088 |
105 |
330 |
Commonly used materials for heat sinks and holders for TEC mounting
Material |
Density g/cm3 |
CTE x10-61/K |
Thermal Conductivity W/mK |
Specific Heat J/kgK |
Ultimate Strength MPa |
Young's Modulus GPa |
Aluminum |
2.7 |
22.5 |
237 |
900 |
50 |
70 |
Copper |
8.96 |
16.7 |
400 |
385 |
215 |
120 |
Kovar |
8.36 |
5.5 |
17 |
460 |
n/a |
n/a |
Cold-Rolled Steel (CRS) |
7.85 |
11.5 |
50 |
460 |
210-240 |
200-210 |
Stainless Steel |
8.01 |
17.1 |
14.5 |
460 |
580 |
n/a |
Cu-Mo(15%-85%) |
10 |
6.9 |
190 |
280 |
540 |
280 |
Cu-Mo(25%-75%) |
9.8 |
8.0 |
175 |
283 |
n/a |
n/a |
Cu-W(10%-90%) |
17 |
6.7 |
180 |
163 |
560 |
330 |
Cu-W(20%-80%) |
15.65 |
8.5 |
200 |
n/a |
490 |
280 |
Brass |
8.49 |
18.0 |
110 |
343 |
240-400 |
102-115 |
Solders
Material |
Melting Point °C |
Density g/cm3 |
CTE x10-61/K |
Thermal Conductivity W/mK |
Specific Heat J/kgK |
Electric Conductivity 106 1/Ohm |
Bi50% Sn25% Pb25% |
94 |
9.44 |
20 |
16 |
151 |
1.7 |
In52% Sn48% |
117 |
7.3 |
24 |
73 |
233 |
9.4 |
Bi57% Sn43% |
138 |
8.58 |
19 |
41 |
180 |
1.7 |
Sn50% Pb32% Cd18% |
145 |
8.8 |
26 |
35 |
205 |
7.5 |
In100% |
157 |
7.31 |
29 |
86 |
243 |
13 |
Sn63% Pb37% |
183 |
9.3 |
26 |
50 |
170 |
7.2 |
Sn91% Zn9% |
199 |
7.27 |
25 |
61 |
256 |
3.9 |
Sn95% Sb5% |
230 |
7.25 |
31 |
63 |
221 |
6.9 |
Thermal Greases (typical)
Material |
Thermal Conductivity W/mK |
Resistivity Ohmcm |
Temperature range °C |
Lifetime years |
Silicone (ZnO) |
0.7 |
>5x1014 |
<150 |
5 years @25C |
Non-Silicone (Al2O3) |
2.0 |
>1013 |
<150 |
1 year @25C |
Non-Silicone (AlN) |
4.0 |
>1013 |
<150 |
1 year @25C |
Epoxies (typical)
Material |
Thermal Conductivity W/mK |
Resistivity Ohmcm |
Die-Shear kg/sm2 |
CTE x10-61/K |
Temperature range °C |
Epoxy (Ag) |
1.35 |
0.05 |
45 |
49 |
-55...+125 |
Epoxy (Al2O3) |
1.73 |
>1x1014 |
105 |
140 |
-20...+130 |
Epoxy (Al2O3) |
1.73 |
n/a |
105 |
140 |
-20...+130 |
Epoxy (AlN) |
3.6 |
n/a |
125 |
120 |
-25...+130 |
Epoxy (Ag+ceramics) |
>7.5 |
n/a |
n/a |
n/a |
-40...+150 |