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CONSIDERATIONS FOR EPOXY AND URETHANE POTTING/CASTING
COMPOUNDS
The following are key considerations in selecting materials for potting or
casting components.
Casting or Encapsulating is a process where a specific device, such as a coil
or a printed circuit board, is placed into a mould. The mould is filled with the
epoxy or urethane encapsulating compound and allowed to cure. The solid block of
epoxy or urethane, containing the device, is removed from the mould for further
processing. The finished component is free standing, without the mould and it is
protected only by the cured encapsulating material during its service life.
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Encapsulant |
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Mould |
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Potting is a process where an assembly is placed into a
case or container and then filled with the epoxy or urethane compound. The container forms part of
the finished unit and remains part of it throughout its service life.
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The following should be reviewed during the material selection
process:
| ITEM |
Examples |
Important material Properties |
| 1. |
Type of
components mounted on the device |
-Pressure sensitive |
-Shrinkage. |
| -Heat generating |
-Thermal conductivity. |
| -Heat sensitive |
-Exotherm during
gellation. |
| 2. |
The
environment the part will operate in. |
-Temperature extremes |
-Ability to thermal
cycle. |
| -Contaminants |
-Chemical resistance. |
| -Mechanical forces |
-Tensile , elongation,
HDT. |
| -Electrical demands |
-Dielectric strength. |
| -Humidity |
-Moisture absorption. |
| 3. |
The amount of
material required per device. |
-Large |
-Pot life, viscosity, exotherm, processing temperature, cure time. |
| -Small |
| 4. |
Shape of the
device. |
-Complex |
-De-airing, viscosity, processing temperature. |
| -Simple |
| 5. |
The wall
thickness of the encapsulant |
-Uniform |
-Cure time, tensile strength, elongation, shrinkage, gel speed viscosity
(filler content) |
| -Variable (heavy & thin) |
| 6. |
Adhesion to internal
external components |
-Trapped air |
-Viscosity,
gel time, pot life |
| -Hard to adhere to
surfaces |
-Viscosity,
shrinkage, gel time |
| 6. |
Processing
requirements |
-Hand mix |
-Mix ratio, gel time, pot life, de-air ability, abrasiveness, viscosity |
| -Machine Dispense |
| 7. |
Curing
possibilities |
-Room temperature |
-Gel time, cure time, shrinkage, tensile strength, elongation. |
| -Heat cure |
| -U.V. cure |
| 8. |
Device
mounting inserts |
-Mechanically supported |
-Exotherm, shrinkage |
| -Supported by encapsulant
only. |
-Tensile,
elongation, TG, HDT, shore hardness. |
| ITEMS
UNIQUE TO POTTING |
| 9. |
Adhesion to
the case |
-Case material |
-Thermal expansion, contraction, gel time, exotherm, tensile strength,
elongation. |
| -Internal surfaces |
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Disclaimer: The above information is general in nature and is based solely on experiences by Crosslink Technology Inc. The recommendations provided herein may not be applicable in all situations. They are provided to the recipient as part of our customer service and the user must determine the relevance of the information to his/her application, considering any limitations that may be applicable thereto. Crosslink
Ttechnology Inc. does not accept any liability for direct or consequential damages resulting from the the implementations of these recommendations or the use of this information.
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