Mounting with Thermal Conducting Adhesives
A Better Solution for Mounting Parts to the Heat Sink
Thermally conductive adhesives offer a new solution to replace traditional mechanical assembly. These adhesives allow for the permanent assembly of similar and dissimilar substrates and simplify the assembly procedure.
Advantages of thermal conducting adhesives:
- Simple and reliable
- Repeatable in production
- Cost advantage over clip & screw
- Improved reliability of power supplies
- Applicable to a variety of packages
Typical Package Mounting Examples
 Liquid adhesive |
 Double-sided tape |
General Application Guidelines
When evaluating thermally conductive adhesive there are some basic attributes that need to be taken into account:
- Thermal conductivity
- Bond line thickness
- Adhesion strength
- Curing conditions
- Storage and shelf life
Adhesives with higher thermal conductivity offer better thermal performance. It is suggested to have a thermal conductivity in the range of 3-5 W/m-K.
A typical bond line is in the 2-7 mil thickness range. For improved thermal performance (lower Thermal Resistance), a thinner bond line is suggested. A thinner bond line can reduce the adhesion strength, so each application needs to be tested to find the correct balance between bond line thickness, thermal resistance and adhesion strength.
It's important to have a uniform bond line thickness for optimal adhesive performance. Good bonding strength is necessary when attaching the IC with the adhesive. A product with higher viscosity offers superior adhesion strength. Curing has to be done according to the data sheet recommendations. If the part does not get cured correctly, it can lead to higher thermal resistance of the assembly, resulting in poor thermal performance. It's also important to take into account the storage temperatures and shelf life specifications of the material selected.
Comparison of Double-Sided Tapes
| Vendor | MPN | Tape Thickness (mm) | Thermal Conductivity (W/m-K) | Dielectric Strength (kV/mm) | Adhesion Peel Strength (N/cm) |
|---|---|---|---|---|---|
| 3M | TM-670SA | 0.25 | 0.6 | 24 | 5.5 |
| 3M | TM-671SA | 0.375 | 0.6 | 24 | 9.3 |
| 3M | TM-672SA | 0.5 | 0.6 | 24 | 11.6 |
| 3M | 8805* | 0.125 | 0.6 | 26 | 7.5 |
| 3M | 8810* | 0.25 | 0.6 | 26 | 13 |
| 3M | 8815* | 0.375 | 0.6 | 26 | 19 |
| 3M | 8820* | 0.5 | 0.6 | 26 | 26 |
Shelf life: 2 years
Comparison of Liquid Adhesives
| Vendor | MPN | Thermal Conductivity (W/m-K) | Shelf life (mos.) |
Storage Temp. (°C) | Dielectric Strength (kV/mm) | Operating Temp. Range (°C) | Curing Temp. (° C) | Curing time (min) |
|---|---|---|---|---|---|---|---|---|
| Dow Corning | DA-6534 | 6.8 | 4 | -10 to -25 | -40 to 200 | 150 | 120 | |
| DA-6524 | 2.1 | 6 | -10 to-25 | -40 to 200 | 150 | 60 | ||
| TC-2030 | 2.6 | 12 | <40 | -40 to 200 | 130 | 60 | ||
| Timtronics | 813HTC | 2.7 | 4 | 25 | 20.07 | 270 | 150 | 30 |
| 816HTC | 2.7 | 24 | 25 | 16.53 | 150 | 25 | 2880 | |
| Aremco | 556-HT-SP | 3.5 | 6 | 25 | 230 | 177/149 | 60/120 | |
| Creative Materials | 116-04A / B-187 | 2.63 | 12 | 20-25 | 18.7 | 100 | 30 | |
| 122-07 (SP) | 5.5 | 2 | 25 | 17.32 | -55 to 230 | 150 | 60 | |
| 109-12 | 5.65 | 1.5 | 25 | 19.48 | 121 | 240 | ||
| Bergquist Company | Hermitage | 5 | 150/160 | 20/6 | ||||
| Springtime Blue | 3 | 150/160 | 20/6 |
Mounting with Double-Sided Tape
1. Clean device back surface with alcohol |
2. Clean heat sink surface with alcohol |
3. Cut the tape according to required dimensions |
4. Apply the tape to one substrate |
5. Peel off the liner on other side |
6. Attach the device to the heat sink and apply clamping pressure |
Mounting with Liquid Adhesives
| 1. Clean device back surface with alcohol |
2. Two part epoxy syringe |
3. Two part epoxy (Part A & Part B) |
4. Mix adhesive solution |
5. Apply thin layer of adhesive |
6. Attach device to heat sink with clamping pressure and allow sufficient time to cure |
Effect of Adhesive to Thermal Resistance
The thermal conductive adhesives tend to affect the effective thermal resistance of heat sink assembly. Refer to the following table comparing the thermal resistance between junction of the device to the heat sink of different thermal conducting adhesives as compared to that mechanically mounted with the clip and screw with thermal grease. The thermal resistance of the device is calculated using the device junction temperatures, heat sink temperature and total power dissipated on the device.
| Mounting Method | ||||||
|---|---|---|---|---|---|---|
| Device Thermal Resistance | Thermal Grease with Mechanical Clip | 8805 (Tape) |
8810 (Tape) |
Hermitage (Epoxy) |
Springtime Blue (Epoxy) |
816HTC (Epoxy) |
| Thermal Resistance MOSFET Junction to Heat Sink (°C/W) | 2.955 | 7.057 | 9.589 | 2.733 | 3.018 | 3.776 |
| Thermal Resistance Diode Junction to Heat Sink (°C/W) | 2.034 | 6.042 | 7.839 | 1.784 | 2.157 | 3.097 |
Recommended vendors:
| Vendor | Contact Information |
|---|---|
| Dow Corning Corporation | Corporate Center PO Box 994 MIDLAND MI 48686-0994 United States General Inquiries/Reception Direct Dial: +1 (989) 496-4400 Product/Price Related Inquiries +1 (989) 496-7875 Toll Free: 1-800-248-2481 http://www.dowcorning.com |
| Timtronics | 35 Old Dock Road Yaphank, NY 11980 USA +1 (631) 345-6509 info@timtronics.com http://www.timtronics.com |
| Aremco Products Inc. | 707 Executive Blvd. Valley Cottage, NY 10989 USA +1 (845) 268 0039 +1 (845) 268 0041 (FAX) http://www.aremco.com |
| Creative Materials Inc. | 12 Willow Road Ayer, MA 01432 USA Toll Free: 1-800.560.5667 +1 (978) 391-4705 (FAX) International +1 (978) 391-4700 info@creativematerials.com http://www.creativematerials.com |
| Bergquist Company | Thermal Interface Material 18930 W. 78th Street Chanhassen, MN 55317 USA Toll-Free: (800) 347-4572 http://www.bergquistcompany.com |
| 3M | 3M Corporate Headquarters 3M Center St. Paul, MN 55144-1000 USA Toll-Free: 1-888-3M HELPS (1-888-364-3577) http://solutions.3m.com |
