Batch cleaning PCBs  - Page 1
Forum section: electronics / general

author: hp23
author_rank: Contributor
timestamp: February 02, 2025, 04:09:30 am
content: Hi Have a great deal of PCBs that require cleaning (30-40 a month). I'd have put these in an ultrasonic bath except having reviewed the datasheets for the inductors I use (Wurth electronics), they state 'washing agents used during production might damage or alter the characteristics of the wire insulation, marking, or plating. Such agents may negatively affect the long-term functionality of the product.'.IPA and a brush is tedious. For info. I use Kester lead-free & Chipquik smd291snl250t5.Any thoughts as to what I should do?Pete

author: b177
author_rank: Contributor
timestamp: February 02, 2025, 04:39:51 am
content: Can you switch to water-soluble paste? it will be easier to clean than a no-clean paste

author: hp23
author_rank: Contributor
timestamp: February 02, 2025, 07:15:18 pm
content: Thanks. I guess i've been a bit dumb. Recommendations on good lead free water based solder pastes? Started with Kester (I've been converted). WP616 looks like a good choice if I can source it in the UK. Thoughts?

author: Kean
author_rank: Unknown
timestamp: February 03, 2025, 01:38:40 am
content: If using certain solvents are the concern, then manual IPA cleaning may also not be ideal.You can get a number of alternative cleaners that are water based but work with all types of fluxes.I use Electrolube SWAS on some PCBs where it is required for cleanliness (high impedance) or other aesthetic reasons, rinsing with deionized water, then drying in a low temp oven.https://electrolube.com/product/swas-safewash-super/https://electrolube.com/knowledge_base/swas-technical-data-sheet/Maybe chat with Electrolube and Wurth about options.I otherwise avoid cleaning if it isn't required (other than spot IPA cleaning after rework), and thus avoid water-soluble fluxes that have mandatory cleaning within a specified timeframe.

author: tooki
author_rank: Super Contributor
timestamp: February 03, 2025, 01:50:46 am
content: Another thing to consider is ChipQuik’s water-washable no-clean flux products. They come off great in 60C water in an ultrasonic bath, but when used properly, don’t mandate cleaning.SWAS is great. But it can be aggressive, I have seen it dull the surface of black IC epoxy. I cannot say for absolute certain if it was actually attacking the surface, or if the surface came from the factory with a layer of coating of some sort.

author: Kean
author_rank: Unknown
timestamp: February 03, 2025, 02:20:43 am
content: Yeah, the finish after cleaning in SWAS is pleasing... "sparkling like a diamond". I've not noticed any changes to surface finish, just impressive cleanliness with little effort.I've had just the one 5 litre bottle of SWAS that I bought nearly 10 years ago. Probably way past its recommended shelf life now. I do dilute the SWAS with deionized water, and top up the levels in my ultrasonic cleaner from time to time depending on the results. I have a dedicated small ultrasonic cleaner for it, so I don't bother to empty the tank after use.I've totally disposed of the solution just a few times over the years, cleaned out the bottom of the tank, and refreshed the solution. I haven't actually used it in the last year or so due to the focus of my recent projects.

author: SMTech
author_rank: Frequent Contributor
timestamp: February 03, 2025, 08:59:03 am
content: I have been issued thishttps://bltcircuitservices.co.uk/product/aim-ws488/by a client a couple of times. It seemed to work just as well the BLT no-clean we use day to day and it cleaned off easily.We typically don't clean SMT (for some reason Americans love to) with pastes from BLT/Solderking/Warton that we have used over the last decade the flux residues are minimal and really only easily distinguished on unpopulated pads. They're harmless and the jury seems to be our on whether it matters if you leave them there before a conformal coat.

author: b177
author_rank: Contributor
timestamp: February 04, 2025, 09:59:31 pm
content: Hopefully this isnt too off-topic, but I am curious if pcb cleaning, say ultrasonic + Safewash, can remove stray solder balls? I've seen a few stuck on my boards and I get concerned about balls getting stuck between fine pitched components and causing shorts. Obviously working w/ the assembly house is first line remediation. But any thoughts on board cleaning as secondary improvement action?

author: Kean
author_rank: Unknown
timestamp: February 04, 2025, 10:14:42 pm
content: Quote from: b177 on February 04, 2025, 09:59:31 pmGenerally yes, as those stray balls will often be held in place by a small amount of dried flux.Note though that the cleaning could actually release a ball behind/between pins that is now free to move but possibly cannot escape to be washed away. Worst case scenario.

author: b177
author_rank: Contributor
timestamp: February 05, 2025, 06:01:43 am
content: Kean: you said you are diluting the SWAS with diH2O. Do you have a estimate for the dilution ratio that you find works well for no-clean flux?thanks,

author: tooki
author_rank: Super Contributor
timestamp: February 05, 2025, 07:04:13 am
content: Quote from: Kean on February 03, 2025, 02:20:43 amWhy do you dilute SWAS, given that the instructions say that diluting it is not recommended?

author: tszaboo
author_rank: Super Contributor
timestamp: February 05, 2025, 04:05:50 pm
content: Quote from: b177 on February 04, 2025, 09:59:31 pmYou can get rid of solder balls with ultrasonic cleaning.I don't know how long it's needed. I only sent back the boards because they had too many solder balls, and it's not acceptable.

author: Kean
author_rank: Unknown
timestamp: February 06, 2025, 12:36:09 pm
content: Quote from: b177 on February 05, 2025, 06:01:43 amGood question, and I can't remember. I may have some notes. I'll try remember to look when I have time on the weekend.Quote from: tooki on February 05, 2025, 07:04:13 amI don't recall, but I thought at the time I bought it there was some document that suggested it. I'd have to go back an look.Maybe the recommendations have changed. Maybe I'm a cheapskate...

author: tooki
author_rank: Super Contributor
timestamp: February 06, 2025, 04:35:05 pm
content: Is it possible you’re confusing SWAS and SWAT?SWAS is sold ready to use, dilution expressly not recommended.SWAT is concentrate designed to be used diluted.

author: Kean
author_rank: Unknown
timestamp: February 07, 2025, 05:50:10 pm
content: Quote from: tooki on February 06, 2025, 04:35:05 pmYes, that is probably it! It sounds like I downloaded/read the wrong docs.I still got pretty decent results, so the diluted SWAS worked fine for me. I confirmed I bought SWAS per my supplier order/invoice and the labeling on the container.