One of the characteristics of parylene coatings is the capability of producing coatings of very small thickness for electronic applications and for medical applications. Sometimes these applications reach very high voltages and require protection for various system parts. In this way parylene is outstanding since it is one of the world leaders regarding the thickness of electrical insulation.
The behavior of parylene coatings as a function of the thickness of the coating may be seen in Table 4. In these tests the breakdown voltage of the parylene coating was measured, for various thicknesses, in a coating applied to electrical circuits. There can clearly be seen from the results the impressive behavior of parylene coating: Starting from a thickness of 7.6μ the resistance to breakdown voltage virtually does not change and is identical over a range of thicknesses up to 50.8μ.
The breakdown voltage is measured as set forth in the following MIL specifications: MIL-I-46058C, MIL-STD-202, and in accordance with this standard using the 106 method.
The test method included cycling of exposure to humidity and testing. In the table there appear test results for breakdown voltage over 10 cycles (the length of every cycle is 24 hours), where every cycle includes 7 stages: the first stage at low temperature and low humidity (25C°, 50% RH) up to the 7th stage of high temperature and high humidity (65C°, 90% RH). The thicknesses of the parylene on which the tests were conducted were between 2.5 microns and 50.8 microns.
The following is a graph that presents breakdown voltage against coating thickness for parylene N and parylene C, as tested in accordance with ASTM-D-149.
Simtal's experience in applications that require high electrical insulation
Simtal has conducted a number of coatings for applications that required high breakdown voltage. For an application of a transformer for a breakdown voltage of 6000V, Simtal made a parylene C coating of thickness of 40 microns that met the target without any problems.
Electrical insulation after exposure to humidity − One of the requirements of various civilian industries is electrical insulation even under conditions of high humidity, that presents an obstacle for various coatings. In Simtal we were required to coat an application implemented in areas of high humidity in which a breakdown voltage of 5500V is required. Countersinking was made for an identical thickness of 40.2 microns and a test that was conducted of constant and protracted flushing/ pouring of 70 liters of tap water during 15 minutes with a permanent connection and also of pulses of 5500V did not lead to any breakdown whatsoever in the coating, nor to any degradation of the insulation capability of the coating. (Due to secrecy requirements, documentation of these tests cannot be presented.)
Electrical insulation also at 12000V − For another customer, counter sinking was done at a thickness of 70 microns on an electronic circuit, and in a standard test of the breakdown voltage of this circuit the aforesaid withstood a breakdown voltage of 12000V!.
Another example of an application of development of a switch for a detonator that makes a very interesting use of the capability of the parylene to hold a high breakdown voltage:
In their research, the developers wished to produce a detonator having the following characteristics:
Resistance to a voltage higher than 1500V.
The switch is required to rapidly discharge the high voltage in a period of time less than 10 nano seconds
The switch is required to be operated by means of a voltage less than 50V.
The switch is required to match conventional and simple production methods, having a monolithic structure, that uses conventional micro electronic technologies. It is absolutely forbidden to use energetic materials for production of the switch.
A reliable switch used for one-time reliable use.
By means of the parylene and because of its electrical insulation capability, the researchers succeeded in producing a switch that behaves like a type of capacitor that very rapidly releases its entire voltage only after breakdown of the coating that is applied at a given thickness for the construction of the required insulation.