App. 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
used extensively in computer an 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
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 (>'l 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
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's could drop to a resistance
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 of 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 ofthe 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 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.