Why ic pins ( on hdd / mboard ) are not covered by lacquer to avoid short circuit ?

No. That holds in heat which will damage a board. You aren't using the boards properly, if you are having that problem. The only boards I ever coated were to be used in space.

Conformal coat is also used when a board will be in a humid environment.

But sprinkling conductive dust over your equipment is a Bad Idea, conformal coat or no (that's why it's called "humidiseal", not "machining chips -i- seal"). The solution may be as easy as vacuuming regularly; if that doesn't work start thinking about good filters, with or without putting your processors into a different room or box from whatever process is generating the conductive dust.

Put the covers back in your gear. Move your computer away from that hostile environment e.g., into an equipment cabinet/closet or put it on a high shelf.

If you can't isolate the gear from the harsh environment, MAKE YOUR OWN INTAKE FILTER. Construct it out of e.g. chicken wire covered with foam. Make it LARGE so that it encases the entire back of the unit; this will give a longer interval between cleanings. Make 2 of these so you can swap one out to clean it with zero downtime.

As others have mentioned, this is a PITA. Don't layer band-aids onto the problem. Examine instead how you are currently doing things.

:I think hdd & mboard makers don't want their products to last longer :than their warranty periods, so users must buy new models. :My mboards / dimms / hdd all have short circuits caused by carbon :in dust on ic / regulator 's pins, I never saw a dustproof casing on :sale. :Does any1 here put lacquer on his ic / regulator 's pins when these :are still new & dust free ? :

If your MB is covered in dust sufficicient to cause shorts across regulator pins

- actually it will most likely only short when the dust is moist - then I wonder how much dust is clogging up your fans and other sensitive devices. You should know that dust is the enemy of electronics and it is the user who has to take all necessary steps to minimise the ingress of dust. When I see a tower PC sitting on a carpetted floor I just know that this is a recipe for disaster. Keep your PC on the table top (or at least 30cm above the floor) and you will find that dust ingress will be minimal (providing it isn't in an abnormally dusty environment).