Potting Compound Selection
The selection of a potting compound to embed the unit is based on the end use, the environment the unit will experience, the number of units potting per hour and the design of the unit.
Here is a list of questions which will provide the information for the potting compound supplier to make a suggestion of a resin system.
1. Is the unit a electronic part, a transformer, a high voltage coil?
2. If the unit is an electronic part does contain a PC board with surface mount components (SMT) and will it be exposed to temperature below 0°C? If the answer is "yes" then the Tg of the potting compound defines what potting compounds could be used.
3. What is the highest operating temperature of the part? This defines the type of resin system to use.
4. Does the resin system need to be flame retardant? Does it need to have Underwriters Laboratory recognition? This further defines the resin system and reduces the selection and increases the cost.
5. Is high thermal conductivity required? If so, please read the discussion on thermal conductivity before making this one of your requirements. If high thermal conductivity is required the cost of material and processing will increase substantially.
6. What are the dimensions of the part and how much potting will be used per part? See how to estimate the amount of potting compound to be used in the unit. This will define the hardener used or if a one part material can be used.
7. How many parts will be made per hour? How long a time before the part needs to be handled? These answers with the amount used per part will define the a) gel time required of the potting compound and b) if a hand pour will be used vs. a MMD machine pour. With a hand pour operation selection of the potting compound should be for along gel time, a long gel time, easy ratio and similar viscosity’s so that the system is more forgiving. If you will use a meter-mix–dispense machine are you prepare to spend the money and the time to maintain the machine? If high speed production is required you may be required to have tunnel ovens or a batch oven with trays of potted devices.
8. Are there sensitive parts that will be potted? Define the sensitivity i.e. if heat, how high, if pressure, how much? This defines the exothermic heat of the potting compound or the shrinkage of the potting compound.
9. Is the potting to be done at room temperature or can it be oven cured? Some systems are only oven curing so this defines the list of systems that can be used.
10. What environment will be potted part experience? We have discussed temperature, but what about chemicals, pressure, vacuum (space applications), water and sunlight? These also determine the type of resin systems needed.
11. Is color important? Many potting systems are black, is that acceptable? Does the potting need to be clear to see through it? If color other than black is an important factor it will limit the resin systems available to you. However, if your usage is high, 300,000 lb./yr., then most suppliers will make the material any color.
Know what is the cost of the potting per part that you can afford? Estimate this cost and asked the resin supplier the cost per cubic inch or cost per cubic centimeter.
The configuration of the unit is also a factor. If there are small spaces the viscosity may be a dominating factor. Therefore, it is a good idea to send the potting compound supplier a unit or a prototype unit to determine how the potting compound will flow in to the unit. Then have it sent back to you so you can test it.
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Last Modified: July 20, 2012