Hello Tom
I have been wave soldering and robotic selective soldering circuit boards using no-clean fluxes for many years.
forget about not spraying flux on the bottom of the wave because then you'll have flakes stuck all over the hot surface of the wave pallet.
There are No-clean fluxes and there are cleanable No-clean fluxes.
The cleanable fluxes will allow you to clean the batch of pallets at the end of the run to prevent a build up of burnt flux.
The two basic spray fluxers that work best because they spray a more vertical spray pattern to avoid shadowing by the walls of the pallet, clinched leads or tall SMT parts.
1. USI Ultrasonic spray fluxer sold direct, Manufactures in Haverhill (Bradford) MA or sold through Electrovert as part of the wave solder system.These are rock solid and their design prevents clogging as there is no spray nozzle only flow restrictors and self clean cycle. You can buy a single or dual port system.
- The two port system allows you to switch either to Port A for OA or Port B for No-clean.
- The other option is to use the external fluxer for two No-Clean fluxes and use a foam fluxer for OA. Just remove the foam flux nozzle and cover so non of the No-clean flux drips into the OA tank.
2. The other system is the Vitronic Soltec ultrajet, a bubblejet system. This is a single or tandem bubble jet system that is truely vertical. As long as the nozzle is not clogged or partially clogged which makes the stream shoot out at an angle and not hit the leads. If checked and when constantly run the system works great.
With a No-clean the setup recipe for the various conveyor speeds, needed for sufficient contact time, is critical to minimize No-clean residue. The clear residue fluxes and the color of the solder mask will result in how visible the square pattern, the shape of the opening of the wave pallet, is on the bottom of the board. If the system like Electrovert has a hot air knife, alot of the residue is burnt off. I've soldered No-clean boards that look like they just came out of the cleaner.
I've had customer specified No-Clean fluxes that look like crape. Hopefully you can control your own process and not be governed by the customer.
Back to setup: A good simple test vehicle is the bare PCB covered with a low acid PH paper and held flat with another PCB. You can see how much penetration you have for a given recipe. When you peel up the PH paper you should have well defined hole pattern.If it is all smudged and discolored then too much flux was applied. If their are voids at the traverse points as the fluxer head sweeps across then the traverse speed, height of the spray head, pressure or wave pallet design (missing wave pocket reliefs around the selective openings, shadowed the spray.
A test PCB with long rows simm hole patterns of three type hole sizes that represent various components makes an excellent flux test board. The space between the long rows allows a dry spot to tape the PH paper strips. The rows are orientated leading edge to back so you can pick up any issues with traverse speed where there are light areas of flux every three inches if there is no overlap of spray was not in both directions to keep up with the conveyor speed on thin board run at a fast speed.
Your primary PCB supplier should provide with these at no charge. They are just .062" drilled laminate sheets.
I hope this helps. Sorry if it was too much information.
John Goulet
Mfg/Process Engineer NH
----- Original Message -----
From: "Tom Burek" <[log in to unmask]>
To: [log in to unmask]
Sent: Tuesday, December 14, 2010 12:06:38 PM
Subject: [TN] No-Clean flux with a Wave pallet
Season Greetings All,
In the opinion of all the experts out there, are there any issues I need
to be aware of in using a No-Clean flux while using a wave pallet?
I am trying to wave solder some through hole pins on a SMT assembly
(populated 2 sides).
Are there flux spray heads that can limit the flux to the exposed pins in
the wave pallet?
How often do the wave pallets need to be cleaned between each run?
I would be most interested in any stories of disaster or success on this
issue.
Thank you in advance and Best wishes to all for a prosperous New Year.
Tom Burek, CID+
Ametek/VIS
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