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What the flux? Lesser known facts about solder’s little friend.

One of the most simple repairs that an arcade collector will perform is a ‘cap kit’, where you desolder most or all of the electrolytic capacitors on a monitor chassis board to fix a myriad of display issues on your game. Some solders have what is known as ‘flux’ in them, which is an agent to prevent oxidization of the metal joints. Here are some tips for cleaning flux off of a printed circuit board, and why you should do it.

How to clean flux – One simple tip

How about I have an expert give you some advice on how to clean flux off of an arcade PCB – Clay Cowgill. Clay has built numerous ‘kits’ to combine a couple of arcade games into one including multiple versions of Q*Bert, Williams games, and even Star Wars. He knows what he is doing. Here is a quote from him from RGVAC on how to clean Solder Flux.

Solder Flux
(brownish crusted material on the solder-side of the PCB)
Many solder fluxes used in PCB repair and some types of manufacturing are water resistant. They will leave a yellow-to-brownish “crust” on the pins of chips on the circuit board’s solder-side. This is usually the result of a previous repair that was not properly cleaned.

Solder flux can usually be removed with household rubbing alcohol and a toothbrush. Wet the toothbrush with the alcohol, and gently scrub. Repeated applications may be necessary. If available, anhydrous alcohol (used for electronics cleaning) works much faster. Blot the cleaned area with a non-linting tissue (like Kimwipes EX-L) or a clean towel.

There are also commercial cleaners used for flux and grease removal. Some types of cleaners are available from Radio Shack, but are generally overpriced and of marginal quality. A professional grade cleaner like Tech Spray’s “Envi-Ro-Tech 1676” will perform best but can be more difficult for a hobbiest to obtain.

So, to recap, it make take some elbow grease if you use alcolhol, but that is probably the cheapest route to remove flux from a board, instead of a more ‘commerical’ product.

Performing a cap kit takes some time, and although you may never have any issues with flux acting as a conductor and causing some problems on your board, it might be worthwhile to think again and clean that flux. Here are a couple of notes from Alex Yeckley, who is known for his Space Invaders board repair, about the problems he had with flux on a Battlezone board and a Space Invaders PCB.

Battlezone board issues;

…..Now, I’ve had some instances on Space Invaders sound boards where the conductivity of the residual flux from previous repairs would screw up the sounds, but I’ve never seen what I eventually found with the BZ. It turns out that the conductivity of whatever residual flux was left over from a previous reflow was 71 ohms over 0.156″. That’s really conductive, and it was the cause of the problem. I’ve never seen anything that conductive that didn’t have metal particles in it……

Space Invaders board issues;

…..Re-check the in-circuit resistance of a 2.2M resistor. Hmmm, only 1.1M. OK, compare that to a known-good board – hey, that one’s reading 2.2M in-circuit. Yada, yada, yada, pull the socket back off and remove all the components, I have 1.1M across two unpopulated pads! Turns out the no-clean flux was conducting too much. Absolutely no solder involved here, just the no-clean residue! Sand it off, put in a new socket using water-soluable, and it works OK. Three hours of my life I’ll never get back……

Problems with Flux on arcade repairs?

Share your story, I’d be interested to hear the things you’ve seen.

Here are some similar arcade posts

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Comments
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Yeah! no I know what Flux is-LOL
and knowing is half the BAttle!!

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Nice tech post Jeff. I will remember the alcohol trick during my next cap job, thanx.

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Rubbing alcohol and a nylon bristle dremel tip work wonders.

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I just used a toothbrush, and was not overly impressed…maybe because it was used. I will try this as a dremel is one tool I actually have.

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I had a dead input on my Front Line game. I traced the inputs back to the filter board mounted right above the PCB. After re-soldering the headers for all of the inputs, I had an entire new batch of problems. I reasoned that it must be vaporized lead residue in the flux and cleaned the back of the board. All inputs worked correctly from that point foreward…

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That's a good one…

And do you clean that flux off with alcolhol, or something specialty? And did you use a toothbrush, or what sort of item to scrub?

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How about Acetone? Is that too strong?

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I don't know yet, this is the first cap kit I'll be cleaning the flux….the alcolhol I used might not have been the right stuff. But I will be around someone who knows all about that this weekend, I'll try to remember to ask about whether Acetone to clean flux is too strong. My guess is no, considering the other stuff people have told me to use to clean chassis.

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