Optimizing ultrasonic cleaning - Page 1
Forum section: electronics / general

author: mbless
author_rank: Regular Contributor
timestamp: March 10, 2020, 02:41:21 pm
content: There are other posts on here about ultrasonic cleaning, but I never found a definitive answer on cleaning solution/flux compability.I normally soak my assembled boards in IPA overnight and then scrub with a ESD brush to remove flux. It works fine but takes a while given how long I have to soak them in IPA. I now have a batch of 50 boards to assemble, so I figured it was worth it to make the jump to ultrasonic cleaning.The most common setup I've seen is Crest sonicator with Branson EC solution, so I bought a Crest 230HT (45 kHz sweep). I use distilled water heated to 60C, then add 3% solution of Branson EC. I run the cleaner for 30 minutes to degas the fluid before using it. Of course things are not going well, and I'm left with flux residue and white stuff on the solder joints after ultrasonic cleaning (see image below).I run the sonicator for 3 mins per PCB at 60C and rinse the board once done. I've tried rinsing with distilled water and IPA, but both leave junk behind that only gets removed with brush scrubbing. I've tried longer run times, different board locations in the cleaner (all with the basket), putting the board in right after soldering vs an hours later, all to no avail.I did the aluminum foil test several times (other attached image). The first time I did it there was only 2 holes. The next two times, the sonicator really punctured the foil a lot after 1 minute. So it looks like the sonicator is fine.That leads me to the cleaning solution and solder/flux I use. The solder paste isMG Chemicals 4860P 63/37 No Clean, and the wire solder isMulticore 386844 63/37 No Clean. So is the problem the solder I use? I've only seen a few people say that no clean is difficult to remove with ultra sonic cleaning, but I haven't found anybody saying what cleaner, cleaning solution and solder they use that works wellIdeally I just want to run the board through the cleaner and then do a quick water/IPA rinse and dry it. If I still have to scrub it then there's no point to buying a $800 cleaner...

author: asmi
author_rank: Super Contributor
timestamp: March 10, 2020, 03:42:37 pm
content: I recently started using water-soluble flux and so far I'm very impressed with results! It's now much easier to clean the board once I've done soldering - I just rinse the board in a bucket of tap water, then use compressed air to remove water from "sticky" places, like inside connectors, or under BGAs. Sometimes I need to use a bit of IPA to remove remaining bits, but usually vast majority of it goes away with water.

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 10, 2020, 08:32:59 pm
content: I use TS391A10 solder paste.Do my SMD assembly and re-flow.Soak in IPA for 30 minutes or so.Goes into ultrasonic cleaner for 5 minutes. I use Branson EC.Then I do THT assemblies. I use Loctite HYDX flux wire. It is water wash, MUST CLEAN.After THT assembly, I put in another ultrasonic cleaner with a solution of Flux-Off Aqueous for 5 minutes.Rinse, dry.Perfectly clean every time. For me it has to be clean, as I waterproof with urethane conformal coating to waterproof the boards.

author: mbless
author_rank: Regular Contributor
timestamp: March 10, 2020, 11:26:05 pm
content: Quote from: Rat_Patrol on March 10, 2020, 08:32:59 pmSo you use Branson EC with no-clean solder paste as well. I'll try the 30 min soak in IPA first.The Flux-Off Aqueous looks promising as it specifically lists no-clean fluxes and ultrasonic use. Have you tried Flux-Off with the solder paste?

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 11, 2020, 03:20:50 pm
content: Quote from: mbless on March 10, 2020, 11:26:05 pmI was un-impressed with the flux-off to actually clean no-clean flux. Had to leave the boards going for something like 45 minutes to get the job done, which is well past spec on a LOT of components. I called the company on it, and they pretty much said "if you leave it soak long enough, it does work. We can't guarantee it will remove all flux formulas, bla, bla, bla......."I ran through all sorts of solution ratios, no success with the maximum duration of UC cleaning of 6 minutes as listed on the SMD electrolytic caps I use.Technically, once I get to the flux-off tank, it is dealing with water-wash flux only, which could be removed with just RO/DI water, but the flux-off is a saponifier, so it gets off any other manufacturing dirt/oils, etc., which I need for my application.The Branson EC attacks the aluminum heat sinks I use, or I would use it in both applications. The heat sinks go on with the THT mosfets, so that is why I split up the operation. The Flux-Off doesn't bother the aluminum since its only a saponifier.

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 11, 2020, 03:27:58 pm
content: I actually couldn't get the Branson EC to get the no-clean flux either.The soak in IPA is the ONLY solution I have found that works for me. I'm not even sure it needs 30 minutes, but that is usually how long they are in there before I get back to them

author: mbless
author_rank: Regular Contributor
timestamp: March 11, 2020, 04:02:45 pm
content: Quote from: Rat_Patrol on March 11, 2020, 03:20:50 pmI do like the idea of using water-soluble for through hole since you don't have to worry about it getting under surface mount components. Not sure I'll actually make that switch, though. From what I can tell, Louis Rossmann uses Kester 44 wire solder and doesn't have issues using Branson EC in a Crest. I have that on my next purchasing list to try out.Quote from: Rat_Patrol on March 11, 2020, 03:27:58 pmDid you scrub between the IPA soak and ultrasonic cleaning or go straight to UC?I should just ask the 2 companies what no-clean flux their solutions can actually remove

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 11, 2020, 06:26:52 pm
content: I scrub nothingThe first wash after SMD population also gets rid of any solder balls from reflow. Double bonus

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 11, 2020, 06:28:51 pm
content: Don't bother calling the company for Branson EC.When I did, the lady told me "We haven't had a chemist working here in years. Nobody could answer that question."I guess they don't invest much in product improvement...

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 11, 2020, 06:55:19 pm
content: Pic of after the first wash process

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: March 11, 2020, 06:58:11 pm
content: Another thought is your water.Just because its distilled, doesn't mean its really good enough. It should be, I used to use distilled, but I now bought an RO/DI system for pure water.Just a thought.

author: mbless
author_rank: Regular Contributor
timestamp: March 11, 2020, 10:22:32 pm
content: Quote from: Rat_Patrol on March 11, 2020, 06:58:11 pmI have a DI system at work so I'd need a clean container to transport it, but that's another thing to try. Thanks.

author: mbless
author_rank: Regular Contributor
timestamp: March 13, 2020, 03:15:44 pm
content: The 30 min soak in IPA has done wonders for the cleaning! I tested 10 boards and there were only a couple of pads with white junk on it.

author: zerohimself
author_rank: Contributor
timestamp: May 02, 2020, 07:09:22 pm
content: I use a SRA TruPower UC-150D-PRO, with a 3% branson EC. I find it always leaves residue without intervention. However with some basic intervention, it works great. Depending the products you are using YMMV.I use Kester 959t no clean flux with Kester 275 NC solder.I preheat it, then degass for 5 mins.I then submerge PCB's and shuffle to evacuate any larger air bubbles.I then run on a sweep for 5 mins.Remove basket, scrub both sides with a ESD safe brushPut the basket back in, and run for 5 mins (on sweep).remove basket, shake excess fluid back into the Ultrasonic, and submerge PCB's in a 99% ISO batch before low temp(around 150 F) drying in a modified toaster oven.With the brush scrub they come out perfect.