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What method for cleaning a wiped board?

What method for cleaning a wiped board?

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When we get a bad print at SMT, the operator uses the alcoho... - May 03, 2023 by ProcEng1

Look at IPC-7526 - Stencil and Misprinted Board Cleaning Han... - May 04, 2023 by davef

Thank you. I do feel that the document is very lacking in de... - May 04, 2023 by ProcEng1

We typically wipe the boards with a lint free wipe soaked in... - May 04, 2023 by dontfeedphils

I did some further reading yesterday and an ultra-sonic dip ... - May 04, 2023 by ProcEng1

We do the same as dontfeedphils, with the difference being t... - May 04, 2023 by MagyarT

there is no reason to completely clean a circuit board. If y... - May 04, 2023 by Wippsen

This isn't always an option. We do a lot of very fine pitch... - May 04, 2023 by ProcEng1

The idea is you test printing cycles with one board before t... - May 04, 2023 by Auriga2001

At the beginning, we absolutely do this with the first board... - May 05, 2023 by ProcEng1

I re-read the comments and it is unclear what will be the re... - May 09, 2023 by MagyarT

Don't wipe the misprint at all! As you show on the picture, ... - May 11, 2023 by Adam_C

Although I see the advantages in your method, not sure thoug... - May 12, 2023 by MagyarT

It may not be suitable for everything, but should be fine in... - May 13, 2023 by Adam_C

We purchased a Aqueuos machine that I would highly recommend... - Jun 05, 2023 by Mainteneer

Sorry I thought I had replied to this message. I will admit ... - Jun 05, 2023 by Mainteneer

What method for cleaning a wiped board? | 3 May, 2023

When we get a bad print at SMT, the operator uses the alcohol wipes and wipes the paste off the board. Then they use compressed air and another wipe.

In most cases this is sufficient. Most vias are tented, but there still remains some solder spheres in the voids between the pads and the solder mask. Also in some of the larger holes. Even then, it usually isn't a problem, but on a few board designs, getting paste spheres in areas that weren't meant to be printed is an issue.

This isn't the best photo, but you can still see the paste.

Does anyone take any additional steps to cleaning a wiped print besides what I described above? I did try another additional step with some degree of success, but ideally I'd like better results.

Attachments:

balls after wiped board.jpg

What method for cleaning a wiped board? | 4 May, 2023

Look at IPC-7526 - Stencil and Misprinted Board Cleaning Handbook, Misprinted Circuit Board CleaningCLEANING [ https://www.multi-circuit-boards.eu/fileadmin/user_upload/downloads/leiterplatten_design-hilfe/ipc-7526.pdf ]

ITW/EAE says "Typically, the cleaning of misprints occurs by hand wiping the misprinted side or cleaning in a conventional stencil type cleaner. Concerns with this approach include:

* Wiping the misprinted side can wedge or trap solder paste in the solder mask, through-hole vias, and/or into other geometries;

* Numerous quality problems can occur due to lack of control and definition;

* Traditional stencil cleaning machines are designed to remove wet solder paste from stencils. Most stencil cleaning processes do not rinse the stencil with water, or may utilize reused water that can include trace levels of metals;

* Cleaning a production board in a machine designed to clean stencils may result in failure to meet ionic cleanliness standards;

* The stencil cleaning agent is typically not adequate for cleaning reflowed flux residues from the A-side of the assembly."

What method for cleaning a wiped board? | 4 May, 2023

Thank you. I do feel that the document is very lacking in detail. It mostly says "yes, it needs cleaned. Make sure the cleaning process doesn't screw it up". The majority of boards that get wiped are already populated on the other side. So that limits what I can do with them. I tried using a chem-wipe wrapped around the nozzle of a small shop-vac and basically doing the same thing that the under stencil cleaner does. This does remove a large amount of trapped paste, but not nearly all of it.

What method for cleaning a wiped board? | 4 May, 2023

We typically wipe the boards with a lint free wipe soaked in the same under stencil cleaning solution we use in our printer, then run it through our spray-in-air stencil wash.

What method for cleaning a wiped board? | 4 May, 2023

I did some further reading yesterday and an ultra-sonic dip tank seems to be the recommendation, using a BGA cleaning solvent. I am not sure how such a process would affect the populated side of the board.

What method for cleaning a wiped board? | 4 May, 2023

We do the same as dontfeedphils, with the difference being that it goes through a drying program too after stencil wash program (3 mins @ 90 degrees air spray) to dry out the via holes and any trapped liquid from under the components.

What method for cleaning a wiped board? | 4 May, 2023

there is no reason to completely clean a circuit board. If you don't use a professional cleaning machine, you will always have leftover paste. Use a test board until the paste print is ok. You can wipe this off several times until the paste print is OK. You only use a real board when the paste print meets your requirements.

What method for cleaning a wiped board? | 4 May, 2023

This isn't always an option. We do a lot of very fine pitch and often will get a clogged aperture and have to wipe and print again. Also, as we are CM, some of our boards are customer supplied and they do not send any "test" boards.

What method for cleaning a wiped board? | 4 May, 2023

The idea is you test printing cycles with one board before thoroughly cleaning it. The board doesn't get thrown away. You just test print and wipe one board until you get a good print, then thoroughly clean that board. What would you use to clean a populated board? Would that not work for some reason? We have a Aquastorm conveyor wash for populated and misprinted boards.

What method for cleaning a wiped board? | 5 May, 2023

At the beginning, we absolutely do this with the first board. However, we do have some problem child jobs where we end up wiping 1 in 5 prints. When searching the topic, most of what I got was "ultra-sonic" cleaners, but that isn't recommended for populated boards. Thats why I came here for more prospective.

What method for cleaning a wiped board? | 9 May, 2023

I re-read the comments and it is unclear what will be the resolution applied in your case, neither if you use the stencil washer for misprint cleaning purposes. I am just curious. Are you not using your stencil washer to wash the PCBs too? Thinking if you are a contract manufacturer, you will need a couple of things to be able to control this process though. At least the possibility to measure conductivity in the wash and rinse tank, which is one indicator to the cleanliness of the solution/water.

What method for cleaning a wiped board? | 11 May, 2023

Don't wipe the misprint at all! As you show on the picture, what it does is push spheres into vias and between solder mask and pads, making it even more difficult to remove.

What you need is a method which doesn't do that. What I recommend is to put the PCB paste down in a tray with IPA (on some standoffs so it doesn't touch the tray bottom) and wait ~15 minutes. I'm getting perfectly clean boards using this method.

What method for cleaning a wiped board? | 12 May, 2023

Although I see the advantages in your method, not sure though how to deal with the following: 1. Your batch is actually only one board (or panel) - this would not work in a low volume manufacturing environment, unless there are other jobs set up on the machine/line which can guarantee you the 15 minute time window without downtime. 2. Submerging ImAg finished PCBs in IPA would possibly create oxidization and/or tarnishing at least on some areas on the PCB. 3. Automotive, medical and defense customers for a contract manufacturing company would most likely reject this cleaning process without proper documentation and analysis of the effects of IPA over their PCBs or PCB assemblies (one side built).

What method for cleaning a wiped board? | 13 May, 2023

It may not be suitable for everything, but should be fine in most cases. I actually use it in low volume manufacturing. I've said 15 minutes, but in fact it may be less. Also I doubt wipe and some extra cleaning to remove trapped paste is going to be quicker.

As for ImAg, I'm curious about oxidazation/tarnishing mechanizm. Where is the oxygen coming from if the PCB is submerged? If it tarnish, what Ag is reacting with exactly?

Most components are OK to be cleaned with IPA, if submerging is a problem, pour just enough to touch the surface. And I suspect automotive, medical and defense customers will reject cleaning with some unknown/random cleaning solvent and wipes which may leave fibers.

What method for cleaning a wiped board? | 5 June, 2023

We purchased a Aqueuos machine that I would highly recommend to anyone. Before that, we used the ultrasonic cleaners with great success. We'd just run it for 5 minutes (whether the board is populated or not) and let it air dry under a blower and it would be like new.

What method for cleaning a wiped board? | 5 June, 2023

Sorry I thought I had replied to this message. I will admit we took some things for granted in the past. More research has been done to determine how many heat cycles a component can have, if it can be submerged, etc. That said, if you don't have any sensitive components that cannot handle the ultrasonic bath it is a great option.

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