Thermal Greases Application Method
Function & Purpose
Finely polished metal surfaces have micro-grooves and/or slight convex or concave curves that make thermal transfer ineffective. When two smooth surfaces are placed together without the use of coatings, actual surface contact is approximately 10%. The microscopic peaks and valleys create air gaps that minimize actual surface contact and cause poor cooling efficiency, causing premature device failure. Thermal compounds and greases work by filling in uneven contact surfaces of heat generating and cooling devices. The purpose of the thermal compound/grease is to fill the air gaps and reduce the interfacial thermal resistance. This procedure provides up to 100% surface contact.
Selection of the correct Thermal Interface Material (TIM) is critical to the performance for each device. Proper selection is based on various material properties; Thermal Resistance, Voltage Isolation, Service Temperature and Wetting Properties.
Initial Preparation :
Open the container, if you notice settling of the filler or oil on top of the surface, material should be stirred thoroughly with a spatula before use. Stir the material side by side and top to bottom to make sure material is homogenously mixed.
The smoother the matting surfaces, the thinner the layer required. Micro processors and/or heat sinks with normal irregularities require a layer of 0.003” to 0.005” film to fill the fabricated gaps.
Approximately amount of material required.
1 mil (0.001”)
5 mil (0.005”)
- Clean mating surfaces thoroughly with a low residual solvent; Heptane, Mineral Spirits or 99% Pure Isopropyl Alcohol. Use a lint free cloth. Oils or Petroleum based cleaners should not be used such as WD-40, Citrus Based Cleaners and most automotive type degreasers.
- Surfaces must be completely dry. Surfaces must be kept free of all foreign materials. Do not touch surfaces since oils from fingers can adversely affect the performance. Fingerprints can be as thick as 0.005”, preventing the micronized particles from directly contacting the metal surface.
Application Tools :
Small Surfaces – A new clean razor, flat edged knife or similar smooth edged tool.
Large Surfaces - Clean putty knife or similar flat edged tool. Small rubber rollers can be used for larger areas.
Small Surface Areas: (CPU’s, Diodes, Transistors, etc.)
Squeeze small amount of thermal grease onto the center of the device. Using the proper application tool spread the grease evenly over the whole device surface area.
With the use of a clean plastic bag, thoroughly rub the compound over the surface using both clockwise and counter clockwise finger motions. This procedure will insure optimum filling of the microscopic valleys in the metal.
Squeeze another small amount of grease, enough to apply a thin film on the center of the device. Using the proper application tool spread the grease evenly over the whole device contact surface. The smoother the matting surfaces, the thinner the layer required. Micro processors and/or heat sinks with normal irregularities require a layer of 0.003” to 0.005” film to fill the fabricated gaps. Properly lapped heat sinks with mirror finishes require only a translucent haze over the entire surface.
Press the two surfaces together, minimizing any “twisting” or lateral “sliding” actions to avoid forming small air voids in the grease film that increase thermal transfer resistance. Secure the two surfaces with the supplied clips, screws or other hardware. Using a lint free cloth, clean all edges, removing any excess grease that has been squeezed out.
Large Surface Areas; (Large Heat Sink, IGBT’s, SCR, TEC, etc.)
Squeeze small amount of grease on the center or corner of the device in a “bead” or “string” form. Using the proper application tool spread the grease evenly over the whole device surface.
The correct, measured amount of applied grease and film thickness for each design application is determined through a series of test experiments. Thermal resistance will be increased if the grease layer is too thick. When the correct amount is accurately established, a very small amount of compound should appear around the perimeter of the device as it is slowly torque down or clip mounted to the heat sink.
The excess compound should be carefully removed, as indicated above.
Alternative Application: “SILK SCREEN” or “STENCIL” and Automated dispensing methods are available for faster and cleaner applications. Please contact Timtronics for further details.
Thermal Pads & Gap Fillers Application Method
Thermal pads and solid gap fillers are manufactured and supplied with protective plastic or paper liners. Remove the liner from one side; apply on part and remove the liner from other side.