Moisture-proof coating agent for switching power supplies, Humiseal


When using a switching power supply in a humid country such as Southeast Asia or along the coast, a power supply with a moisture-proof treatment on the power supply board may be selected as a measure against rust caused by moisture and salt.

Power supply manufacturers use “Humiseal” as a coating agent for substrates to prevent moisture.
It is generally used because it has a proven track record and has no particular problems.

What is HumiSeal?

A coating agent developed for military use by Chase Corporation (Humiseal Division) in the 1990s. It has excellent moisture resistance and is widely used as an insulation and moisture-proof coating for substrates, such as in-vehicle substrates and electronic / electrical control substrates.


Chase Corporation

It was founded in 1946 in Randolph, Massachusetts, USA by Chase parents and children.
The first product was rubber baby pants worn on cloth diapers.
Today, it has grown into a leading specialty chemicals company for protective materials with approximately 800 employees.
The production bases are in the United States, Europe and Asia, and Asia has factories in Suzhou, China.


Effect of Humi seal

Applying Humiseal has the following effects.

Moisture proof

In addition to normal humidity, it can also prevent salty humidity in seawater.

Removal of pollutants

Removes air pollutants and protects electronic boards.


Moisture trapped in the circuit board escapes to the outside.


The coating surface is electrically insulated because it is a protective layer that maintains insulation resistance.


How to apply Humi Seal

There are four ways to apply, each with its own strengths and weaknesses.

Brush coating No equipment costs required Workers are required. There is a difference in coating quality. It takes time to work. Only a small amount.
Ditch pickled Suitable for large quantities. Constant coating quality There are only a limited number of things that can be pickled. Masking of a wide area is required.
Spray No equipment costs required. Suitable for large quantities. A little masking is enough. The quality of the coating is determined by the skill of the workers.
Coating equipment This is the most productive and can handle the quantity. The quality of the coating is the most constant. Minimal masking is OK. Efficient because it can be coated only where it is needed. There is a cost to purchase the equipment.

No company has a power supply manufacturer with its own equipment, it is brushed or sprayed by workers.

Substrate Coating

Board coating for switching power supplies is available as an option.
There are two types: “single-sided coating” that coats only the surface of the part and “double-sided coating” that coats the back side as well.

It is basically NG to apply a coating agent to electronic parts.
However, since the power supply manufacturer knows that there is no problem with coating based on its past achievements and experience, it is coated at its own discretion. Of course, I do not apply it to parts that should never be applied.

In the actual work, the worker carefully looks at the work instructions when brushing, and in the case of hand spray, masks and then sprays.

The coating is laborious and requires a place and time to dry. If you do not manage the humid seal after work, it will dry out and you will not be able to use it.