Gap filler vs. Gap padJohn Moot
Gap filler vs. gap pad
In a variety of applications, materials must be used to dissipate heat: New electronic devices and components, for example in the automotive industry or consumer electronics, are becoming smaller and smaller. At the same time, more and more functions are being realised in the smallest possible space.
Thermal management is the keyword for optimisation in this area. Thermal conductive materials can be found in household appliances as well as in commercially available smartphones and tablets or in LED lighting technology. Other areas of application are motor construction, power electronics applications or battery systems in hybrid and electric cars.
Attempts are always made to dissipate the heat from electrical components via improved contacts into a heat sink or into an assembly that functions as a heat sink.
In order to close larger gaps and thus improve heat dissipation, two products are available in principle: Gap fillers and gap pads
What is a gap filler?
Gap fillers are thermally conductive, liquid-applied materials. These thermally conductive gap fillers are often applied by metered mixing of a two-component system with a metering system. Silicone-based, polyurethane-based or acrylate-based systems are often used as a base. Silicone-free gap filler systems based on polyurethane or arcylate are increasingly being used.
Once these materials have been applied, the gap filler cures. Once cured, the material forms a solid but compliant interface that conducts heat away from the electronic components, resulting in longer life and higher performance.
They are often used as a replacement for thermal pads because they achieve lower thermal impedance and offer more design flexibility. Gap fillers are also well suited for high volume production of electronic components such as batteries, inverters/converters, motors and power electronics.
What is a gap pad?
Gap pads are soft, elastic, relatively thick mats with thermally conductive properties. Gap pads compensate for height differences between components through their material thickness and elasticity. Here, too, silicone-based, polyurethane-based or acrylate-based systems are often used as a basis. Silicone-free systems based on polyurethane or arcylate are increasingly being used.
The low self-adhesion of the gap pads, which can be achieved by special settings, enables simplified pre-assembly in many cases. Where stronger adhesive forces are required, self-adhesive versions of the Gappads can also be used. Here it is important to ensure that the adhesive matches the system, i.e. silicone-based, polyurethane-based or acrylate-based adhesive systems are used.
Gap fillers are often applied by mixing a two-component system that is applied to one of the two substrates (e.g. electronic component). This component is then brought together with a heat sink until a certain thickness is reached. The material then forms a solid but compliant interface. It is also possible to fill existing cavities with gap fillers so that no pressure needs to be applied.
Thermal pads, on the other hand, are pre-cut into a desired shape, applied to a substrate, compressed to the set thickness and fixed in place.
The applied compressive load forces the firm but compliant pad to make intimate contact with the rough surfaces of the heat sink, PCB or component. Gap fillers, unlike solid thermal pads, flow into the small valleys, closing surface roughness and creating closer contact with the surface of each component. This allows for more efficient heat transfer between the top and bottom substrates through the use of the gap filler.
Comparing the key characteristics of the two types, the relative cost of using thermal pads is high due to the costly scrap that is created. Gap pads, unlike gap fillers, are first manufactured in mat form and then die-cut or plotted. This inevitably results in more waste. Air entrapment is more common with gap pads because they cannot reach the tiny spaces created by surface roughness.
Gap fillers are the answer for design flexibility because the hardness and application time can be adjusted by the mixing ratio of the two parts of the gap filler. And when it comes to applying the product, the large form factor gap pads can be difficult to apply without trapping air, and automation is difficult. On the other hand, gap fillers are well suited for high volume production.
However, it should also be noted that automating gap filler processing also comes at a cost. Often our customers decide to use prefabricated gap pads as a first step, and then later rely on automated gap filler processing in a large-scale production project.
How can the curing speed of a gap filler be increased?
To increase the cure speed of most gap fillers, potting materials and/or adhesives, the temperature of the part to which the materials are applied must be increased. This can be done with an oven, heat lamp or induction heating. Parts can be preheated to the desired temperature, or the material can be applied first and then the part heated.
As a general rule of thumb, the curing rate approximately doubles for every 10 degrees Celsius increase in temperature. It should be noted that with rigid materials, increasing the curing speed increases the risk of creating high internal stress in the material, which can affect its mechanical strength and its ability to withstand thermal and/or mechanical shock.
In general, we recommend being very careful in determining the temperature profile, as damage to the electronic components may occur in addition to damage to the actual gap filler materials.
What thermal conductivities can be achieved with gap fillers or gap pads?
The gap fillers available on the market have thermal conductivities of up to 7 W/mK with different Shore hardnesses. The Gap Pads are supplied with thermal conductivities of up to 17 W/mK.
Silicone-free and silicone gap fillers and gap pads
The standard delivery programme includes silicone-free gap fillers and gap pads as well as silicone-containing gap fillers and gap pads. There are a number of selection criteria as to which solution is the most suitable.