Silicone's Functional Attributes

When it comes to choosing a sealant, the sensitive components of electronics applications have very specific operational goals. Will fine wires or dense components be endangered by thermal cycling? Will the component be exposed to moisture or dust? Is a printed circuit board meant to withstand intense vibration or impact? Whatever the variables, silicone’s modifiable characteristics make it the ideal material for the job.

 

Hardness

Whether the need is for a material that is very soft to minimize stress to the component, or for an element to be encapsulated with a harder surface coating to protect the sensitive electronics within, silicone is up to the task. Silicones are measured using a durometer and assigned a value on the Shore A scale. The lower the value, the more flexible the material.

 

Tensile Strength

How much stress on your material will cause it to fail? Silicone properties can be calibrated to match the necessary tensile strength to the specific application. A typical range is between 50 psi and 450 psi.

 

Elongation

By modifying the filler composition, silicone can elongate between 50 to 900%.

 

Rheology

Adjusting the thixotropic ratio provides maximum control over a silicone’s viscosity under shear and at rest. A high thixo ratio ensures that once dispensed, the silicone holds its shape until cured.

 

Adhesion

It’s important to discuss adhesion requirements with a silicone supplier to ensure the right adhesion promoter is selected for the metals and plastics most commonly used in electronics applications as well as substrates such as: FR4, PET (Mylar), PBT, polypropylene, copper, aluminum, brass, gold, and stainless steel.

 

Electrical Conductivity

Silicones have excellent electrical insulating (dielectric) properties that help protect electronics from shorting or arcing.

 

Thermal Conductivity (TC)

Silicones can be modified with conductive fillers to encourage heat transfer and mitigate thermal cycling effects. Using standard thermal filler packages, materials with TC up to 5.0 W/mK are possible. Exotic filler packages can extend this performance range well beyond 5 W/mK.

 

Optical Properties

Translucent silicone sealants and conformal coatings look slightly opaque when applied, but cure clear. If tracking during spraying is desired, a UV tracer agent can be added, as can a color filler to conceal sensitive information or meet additional security requirements.

 

At Novagard, each of the above properties can be customized in the lab to meet precise and exacting requirements.