The Essential Guide to Large-Volume TIM Dispensing
Thermal Interface Material
As electronic devices continue to get smaller and the
amount of heat they generate increases, cooling and
temperature control have become critical. Dispensable
Thermal Interface Materials (TIMs) are an excellent
solution for these applications because they provide
outstanding thermal conductivity and greater process
flexibility when compared to thermal pads.
Thermal gap fillers can fill gaps between a heat source and a heat sink to lower overall thermal resistance in a range of automotive, 5G telecommunications, consumer electronics applications, and more.
You’ve selected the right material for your application. Now it’s time to finish strong by choosing the right equipment to dispense it and the right partner to help develop your application.
This guide walks you through essential process considerations and includes popular configuration options to get you started
Effecient Heat Transfer
Bond Line Thickness
Upon close inspection, heat-generating devices and heat sinks do not mate up completely because their surfaces are not perfectly flat.
There are small area(s) of physical contact, but there are many gaps where the air is trapped between the heat sink and the heat source – these pockets of air act as insulation, preventing efficient heat transfer. Thermal interface materials with fillers that provide better thermal conductivity than the air are applied between the surfaces to facilitate heat transfer and avoid this issue.
The bond line describes where a material contacts two surfaces, typically where it is pressed between them. As a rule, the essential quality of a bond line is its thickness. In general, thinner bond lines reduce the distance heat must travel to escape the heat source. Therefore, a thin bond line is preferred over a thick one to minimize thermal resistance.
Filler Materials
Thermal conductivity is expressed in W/m.K (k, λ, or κ). Unfilled polymers have a thermal conductivity of approximately 0.1 W/m.K.
Filler materials offer thermal conductivity between 1-1000 W/m.K. Inorganic particle fillers include aluminum, oxide, magnesium oxide, aluminum nitride, boron nitride, and diamond powder. Metal fillers, notably silver, are also used to enhance thermal conductivity.
Polymers with fillers typically range between 1-10 W/m.K.
| Thermal Conductivity at 77°F (25°C), (W/m K) | |
| Vacuum | 0.000 |
| Air | 0.024 |
| Paper | 0.050 |
| Cork | 0.070 |
| Rubber, natural | 0.130 |
| Water | 0.580 |
| Stainless Steel | 16.000 |
| Zinc Oxide | 25.200 |
| Aluminum Oxide | 30.000 |
| Lead Pb | 35.000 |
| Tin Sn | 67.000 |
| Platinum | 70.000 |
| Aluminum | 205.000 |
| Gold | 310.000 |
| Copper | 401.000 |
| Silver | 429.000 |
| Diamond | 1000.000 |
Large- and Micro-Volume TIM Dispensing
GLUDITEC GCC Series offers large- and micro-volume dispensing of thermal gap filler (gels and pastes). We’ve provided the following tables that outline key process considerations and common equipment types for both large- and micro-volume dispensing solutions for contextual reference. This guide focuses on large volume dispensing of thermal gap fillers. For information on micro-dispensing solutions for thermal grease and thermal adhesives, contact GLUDITEC.
| Material | Typical bond line thickness | Abrasiveness | Typical Volume Dispensed | One component (1K) | Two component (2K) | Reworkable |
| Thermal Grease | < 250 µm | Moderate | *Low | Yes | ||
| Thermal Adhesive | < 250 µm | Moderate | *Low | No | ||
| Thermal Gap Filler (Gels and Pastes) | > 250 µm | High | **High | Yes (Typically one component) |
Equipment
| Material | Time-Pressure | Auger | PCP | Positive-Rod Metering |
| Thermal Grease | ||||
| Thermal Adhesive | ||||
| Thermal Gap Fillers (Gels and Pastes) |
One component |
One & Two component |
Two component |
How much material will you need?
You’ll need enough material to cover the component – or bond area – with a bond line that ensures proper adhesion and performance after the material is compressed. The amount of material to dispense is a simple calculation:
Dispense Volume = Final Bond Line Thickness x Bond Area
However, you’ll need to consider other external factors such as viscosity differences, substrate material composition, and mechanical tolerances that could cause variation in the final bond line thickness. To compensate for those factors, calculate the volume using the upper tolerance limit for your application. When you calculate the volume using the thickest acceptable bond line measurement within tolerance, you’ll ensure that a sufficient amount of material is dispensed between the heat source and heat sink, whether the processed part is at the lower or upper end of the mechanical tolerance spectrum.
When calculating volume, consider the:
- Dimensions of the component generating heat
- Required bond area coverage
- Upper tolerance limit for your application
- Desired final bond line thickness after the material is compressed
Tip: When mechanical tolerances result in a bond line at the lowest acceptable thickness within range, inspect the bond carefully to learn how it could fail and whether performance is affected. Adjust the bond line thickness as necessary.
Choosing a Dispense Pattern
Dispense pattern geometry has a significant influence on process efficiency. Choose a dispense pattern that balances the:
- Dispense speed
- Force required to achieve bond line thickness
- Material usage
- Dispensing equipment capabilities and wear
Make strategic choices. For example, you might choose a more complex spiral pattern that takes more time to dispense if you’re dispensing on a part that has a low tolerance for mechanical stress. In this case, the gain in quality could out weight the impact on UPH.
Our expert applications engineers can help you navigate the options and develop your application to achieve the perfect balance.
| Pattern | Air Entrapment Risk | Programming Difficulty | Common Use |
| Dot | Low | Easy | A single dot per component |
| Line | Low | Easy | A single line covering one or more close-set components |
| Cross | Low | Easy | A combination of two lines covering a large component |
| Wave | Moderate | Moderate | A wave-shape line covering a large area, often between a heat spreader and a heat sink |
| Spiral or Serpentine | Higher | More Complex | These patterns are used to limit mechanical stress on parts. The dispensed shape immediately covers the part, requiring minimal force to achieve the target bond line thickness. |
For more information, please contact us:
Hotline: (+84) 969 469 089
Email: info@gluditec.com