PCB Cleaning advice

[kylehunter]

Hey all,

I need some advice on PCB cleaning. Up to this point, our assembly line has strictly run NC paste, with all SMT parts. We never washed any boards, as no client has requested it this far. We recently bought a selective soldering machine to do more THT. There's no way that I feel comfortable shipping boards after a selective without cleaning them, the amount of flux on the board is significantly more than from SMT.

We are high mix - low volume, so doing 500 boards a week would be a really busy week for us, normally we are < 100 boards per week, so throughput shouldn't be a huge issue.

Our main issue is water supply and sewer. Our space is basically a converted warehouse/garage, that is separate from our office space upfront. This means we do not have a water supply or drainage in our space. Walking to the offices require us to go outside, so doing anything up there is also not a possibility. We also can't spend a ton of money (<$20k or so), so the zero-discharge triton aqueous systems are out. I also don't feel comfortable using ultrasonic cleaners due to the risk of damage. Same goes for full water-soluble fluxes since we do a lot of QFN's with thermal pads, I won't risk leaving residue under them and rusting. So I assume we will use an NC/R/RMA flux.

It seems to me like the only real option we have is to use a vapor-degreaser since they are zero-discharge as they reuse the solvents. I just don't like how they don't seem to be super commonly used nowadays; it seems like it is an "outdated" technology as compared to aqueous cleaning. I found some nice solvents from techspray (ME-1500) that are low-VOC and plastic safe. There's also an AIM article: "New Vapor Degreasing Chemistries to Remove Difficult Lead-Free and No-Clean Fluxes from Modern PCBs" that showcases some of the new solvents that are used. I found some nice machines (not specifically for PCBs, I can't find any that are) that are new for <$10K.

So am I missing something here? Is there a reason to shy away from vapor degreasing for our application? Any other thoughts/suggestions are much appreciated!

Side note: Has anyone used any of Superior Flux's products? They seem like a nice company, all pastes are built to order, and I was actually able to talk to a chemist for an hour picking his brain. I've never been able to talk to a real person at Kester/Loctite before, so that was a nice change!

[Rat_Patrol]

I think you are limited by not having fresh OR waste water facilities.

I suppose you have to measure out if it is better to run some very expensive equipment/procedures or run utilities.

FWIW, I use ultrasonic cleaners on finished PCBs daily, no issues yet. I've put micros and memory chips in the drink and ran them for half a day and they still function. Every report I've read about ultrasonic cleaners is that if you have a sweeping frequency, there is no evidence that they do any harm.

That said, I don't make stuff for the .mil or NASA.

[elecman14]

Hey all,

....There's no way that I feel comfortable shipping boards after a selective without cleaning them, the amount of flux on the board is significantly more than from SMT....

Is your tht process using non-nc flux? If not you may actually be better off with leaving the flux on the PCBA as far as reliability goes. Maybe you should see if your customers complains and the first one that does stick them with the bill for the washer 

[kylehunter]

I think you are limited by not having fresh OR waste water facilities.

I suppose you have to measure out if it is better to run some very expensive equipment/procedures or run utilities.

FWIW, I use ultrasonic cleaners on finished PCBs daily, no issues yet. I've put micros and memory chips in the drink and ran them for half a day and they still function. Every report I've read about ultrasonic cleaners is that if you have a sweeping frequency, there is no evidence that they do any harm.

That said, I don't make stuff for the .mil or NASA.

Yeah... That seems to essentially limit us to really no other choice than vapor degreasing it seems.

I do agree with your statement on ultrasonics, and that has been my experience as well. My issue is this: We would be going from not cleaning NC flux, which some people say is OK, others say is not, to cleaning in a way that some people say is OK, others say not. If/when we get the ability to clean, I want to 100% know that we are doing it in a "safe/proper" way.

Hey all,

....There's no way that I feel comfortable shipping boards after a selective without cleaning them, the amount of flux on the board is significantly more than from SMT....

Is your tht process using non-nc flux? If not you may actually be better off with leaving the flux on the PCBA as far as reliability goes. Maybe you should see if your customers complains and the first one that does stick them with the bill for the washer 

Yes, we are using NC in SMT and THT (would switch to R/RMA for cleaning). Yeah, it's more of an issue for the future (when the client does require cleaning),  and we do have one design in the works that will need to be conformally coated, thus requiring wash.