Application Note 22 - Very High Humidity
- Are Stabilants being used in high-humidity conditions?
- Yes, the Stabilants have been used extensively in high humidity conditions with excellent performance. These applications range from Oceanographic and Sonar equipment, to their use on airborne connectors under tropical and/or engine-mounted equipment conditions. In addition, Stabilants are used extensively in computer and communications applications in tropical countries. All of these were done without special pre-treatment.
- What are the high-humidity conditions where special precautions must be taken?
- Whenever the Stabilants are used on connectors used in high-impedance circuit (typically circuits of 2 Megohms or higher), in an environment where the humidity was in excess of 98% relative humidity and/or in an environment where there was the possibility, because of thermal cycling under humid conditions, such that there could be moisture condensation on the surface of a circuit board.
- What precautions have to be taken before using Stabilant 22 in these conditions?
- This note applies to those applications where it is important to maintain high surface resistance (> 1 Meg ohms/square), such as high
impedance circuitry, or where there are very tight specifications on circuit board operations under conditions of high humidity.
When using Stabilant 22, Stabilant 22A or Stabilant 22E in very-high humidity conditions on applications such as card-edge connectors involving high-impedance circuitry, some precautions should be used to ensure that the material can work to best advantage Because Stabilants have a surface-active property (necessary to remove and hold corrosion by-products in suspension) they could also hold enough moisture such that under very high humidity conditions surface resistance could drop to a value as low as 2 x 1 0 ohms/square.
If this is unacceptable, pre-treatment of the circuit-board surface should be done in order to provide a hydrophobic (water repellent) surface between the contact and/or traces. This can be done by using one of the common fluorocarbon-oil base sprays (such as Scotchguard(TM)- 3M Corp.) to spray the critical area. Then buff off the material from the card-edge connector contacts and apply the Stabilant as usual.
The Stabilant will now be confined to the actual contact area, and the board surface will be sufficiently hydrophobic so as to maintain the required insulation resistance.
It is recommend that the Stabilants be applied only to the male portion of the connector.
An alternative treatment would be to apply the Stabilant material only to the actual metal contact, using only enough to coat the major portion of each contact.
- Field considerations necessitating this pre-treatment.
- Normally, the impedance of most circuitry encountered in TTL or even Cmos circuits is such that this specialized treatment will not be necessary. However, where electrometer or photo-multiplier or similar circuitry is encountered, or where very low leakage is a requirement (such as on Teflon insulated stay-alive batteries for computer memories) the extra time required to apply the hydrophobic fluorocarbon can substantially reduce any leakage under high humidity conditions.
Stabilants™ are a product of Dayton Wright research & development and are made in Canada
NATO Supply Code 38948
15 ml of S22A has NATO Part # 5999-21-900-6937