PCB Washing: Ultrasonic? Dishwasher? Other?

Not sure if this is the right forum or not, apologize if not. The folks on this forum are rather intelligent, so I thought it may be a good place to get some info :slight_smile:

I will be making a short run of some rather large PCBs that need to be waterproofed. They are 150x250mm boards, and there are 2 interconnected boards (same size) that are about 40mm apart.

After manufacture, I need to clean them for conformal coating (going with urethane).

The options I see are:

Ultrasonic cleaners
They seem more aimed at re-work cleaning, such as removing corrosion and such.
Possible damage to old ICs I have to re-use? Lots of conflicting opinions there.

Purpose built PCB washers
They obviously work well, but are stupid expensive. I can’t afford one.

Countertop residential dishwashers
Fitted to run on RO/DI water (need that for rinsing anyway).
Seem to not beat up on the old ICs, but foaming of the cleaning solution may be an issue?

Since I’m only removing fresh manufacturing stuff (flux, fingerprints, dust, etc), I’m leaning toward the residential dishwasher method, maybe with Branson EC cleaner.

Thoughts?

Rat_Patrol:
Not sure if this is the right forum or not, apologize if not. The folks on this forum are rather intelligent, so I thought it may be a good place to get some info :slight_smile:

I will be making a short run of some rather large PCBs that need to be waterproofed. They are 150x250mm boards, and there are 2 interconnected boards (same size) that are about 40mm apart.

After manufacture, I need to clean them for conformal coating (going with urethane).

The options I see are:

Ultrasonic cleaners
They seem more aimed at re-work cleaning, such as removing corrosion and such.
Possible damage to old ICs I have to re-use? Lots of conflicting opinions there.

Purpose built PCB washers
They obviously work well, but are stupid expensive. I can't afford one.

Countertop residential dishwashers
Fitted to run on RO/DI water (need that for rinsing anyway).
Seem to not beat up on the old ICs, but foaming of the cleaning solution may be an issue?

Since I'm only removing fresh manufacturing stuff (flux, fingerprints, dust, etc), I'm leaning toward the residential dishwasher method, maybe with Branson EC cleaner.

Thoughts?

We have a standard Sears dish washer as backup for our circuit board washer. Use regular hot tap water with a bit of dishwasher detergent. When done, use deionized compressed air to blow off excess water. Then air dry. We never use any solvent on any board.

Since you are the designer of the boards, did you confirm by the data sheets that ALL components can be washer?

those are not LARGE circuit boards!

Paul

Interesting problem. I make 10mm x 10mm boards and clean them with 99.99 anhydrous alcohol and a small stiff brush after hand soldering on a limited number of parts that aren't SMD.

Will your boards need that kind of mild scrubbing, or will spraying on cleaner and letting it drip off be enough?

Paul_KD7HB:
We have a standard Sears dish washer as backup for our circuit board washer. Use regular hot tap water with a bit of dishwasher detergent. When done, use deionized compressed air to blow off excess water. Then air dry. We never use any solvent on any board.

Since you are the designer of the boards, did you confirm by the data sheets that ALL components can be washer?

those are not LARGE circuit boards!

Paul

Well, they are large boards for me :smiley:

The DI compressed air is a new thing for me. I figured the air had to be filtered, but I never knew you could de-ionize the compressed air. Off to Google...

Rat_Patrol:
Well, they are large boards for me :smiley:

The DI compressed air is a new thing for me. I figured the air had to be filtered, but I never knew you could de-ionize the compressed air. Off to Google...

The trigger control for the air has an AC power supply box that generates high voltage + and - and the trigger unit has internal sharp points for the + and - voltage to create a neutral air stream out of the output. Regular compressed air is a static electricity generator!

Paul

any particular model I should look at?

I'd rather not spend tons-o-money, but I need the right tools.

Rat_Patrol:
any particular model I should look at?

I'd rather not spend tons-o-money, but I need the right tools.

Got mine years ago on Ebay.

Paul

I too use 99.99% IPA.

Use a paint brush (cut off most of the bristles) to scrub hard to get at places.

‘While the board is still wet’ with IPA, rinse board with water, blow dry with air compressor.

Use rubber gloves.

That works well for smaller boards, but will be burdensome for large quantities of bigger boards.
150x250mm = 37500mm^2.
100x100mm = 10000mm^2

Nearly 4x the surface area to clean. On just one side. I can see how some automation would be handy.

I'd be concerned with air from compressor creating static charge build up.

So for example, this is what I'm looking for:
Amazon Link

I should also ask about the water used for the dishwasher method:

We are on well water (high iron). Do I need to install an RO/DI system that empties into a barrel, and another pump to pressurize that separate water system (go into a hot water heater and the dishwasher, plus rinse sink)

or

Is using regular softened water (salt!!!) sufficient, provided I rinse the PCBs well with distilled water after the wash cycle?

Where I work we assemble PC boards. I don't work in that department but the board-washer sort-of "looks like" a dishwasher with a conveyor belt running through it. I'm pretty sure there is DI water running-into that room and I don't know if they use any detergent.

There's a built-in dryer, probably similar to the heater built-into a dishwasher.

Of course, we use water soluble flux.

Our "standard procedure" for components that can't be immersed in water is to solder them later with "no clean" flux. I think it's ugly!

At another company we hand-washed the boards in a sink with plain tap water and dishwashing brush. Then, we'd use regular compressed air for drying. There was usually moisture in the compressed air so usually we' let the board air-dry a little longer. This was just for occasional rework and sometimes hand-soldering of a few components after wave-soldering or oven-soldering by an assembly house.

Rat_Patrol:
So for example, this is what I'm looking for:
Amazon Link

Yes, have two of those, but much older.

Paul

PS: need dry air or you will contaminate the device.