# Thermal Contact Resistance - Example

In the electronic industry, chips are usually joined to substrates by a thin layer of epoxy. Similar situations are encountered in other industries. Modeling the epoxy layer as a separate component requires the use of a very small element size that can result in meshing failure or an unnecessarily large number of elements.

To consider the thermal resistance caused by the epoxy layer, you do not need to model it. Thermal contact resistance is implemented as a surface-to-surface contact condition. You can either specify the total resistivity or the resistivity per unit area.

## Modeling Thermal Contact Resistance

There are two ways of modeling thermal contact resistance:

• You can neglect the thin layer of epoxy when creating the geometry. In other words, the faces of the components that are separated by the thin layer in reality, will be touching in the model.

• You can consider the thin epoxy layer when creating the geometry. In this case there will be a gap between the faces of thermal contact. When using this approach, there are two points to consider:

• Results are most accurate when the distance between the two contact faces is less than or equal to the element size in the neighborhood. The below example may provide inaccurate results.

• Splitting the faces for proper pairing of thermal contact, although not necessary, improves the accuracy.

• To specify different thermal resistances between a large face and a number of smaller faces, you must first split the large face to a number of smaller faces before assigning thermal contact resistance for different pairs.

To define thermal contact resistance:

1. In a thermal study, right-click Connections and select Contact Set.

The Contact Set PropertyManager appears.

1. Set Type to Thermal Resistance.

2. In Faces, Edges, Vertices for Set 1 , select the desired entities associated with one or more components.

3. In Faces for Set 2 , select the desired faces from another component.

4. Select Thermal Resistance and do the following:

1. Set Units to the unit system you want to use.

2. Select Total or Distributed and type a value.

5. Under Advanced, select Node to surface or Surface to surface. The Node to node option does not allow you to specify a thermal resistance as connected nodes of touching faces will have the same temperature (perfect conduction).

6. Click .

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