# Is flux conductive?...



## eyevancsu

I just got in a pound of 63/37 kester .025" solder from mouser and used on it a few amps, of which none worked. Ive never had this problem before (i used to use some brand i got at frys that was regular 60/40). I figured that the amps werent working because i messed up somewhere, so i checked every possible thing so many times, and nothing except for a horrible dc offset which ive never had. The sound only came out of one side, and i got as much as 6.3v at one side and 2.1v at the other. 

 I was more pissed than anything, so while just messing with the board, i got a small flathead screwdriver and cleaned off in between each trace, i then turned the amp on and voila!, i worked perfect. So i did this to every amp and they all now work.

 So my question...Is the kester flux conductive or something? 

 -ivan c.


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## groggory

I wouldn't imagine it would be. My guess is you might be leaving minute bridges.

 Check your work with a magnifying glass under a bright light and see if you can see any bridges. I can't imagine any company that would want to make conductive flux.


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## fewtch

In the future, you might consider soaking the stuff you build in 99% isopropyl for about a half hour, then dab in between traces/components with a paintbrush (removing any remaining residue) and dry the board using a fan or something. I've heard this procedure recommended to clean off the flux & other surface contaminants.


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## Sovkiller

Alcohol or acetone will clean the flux residues, I had another substance a paint solvent, that is even better I can eve remember the name now...


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## ECM

i use the cheapest can of carburetor cleaner to remove the flux. a quick spray will remove most residue and leave your solder joints looking shiny. be sure not to get it on plastic (so far all my cat5 has survived) or paint since it will melt it. and it dries fast too!


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## eyevancsu

Thanks for the quick replies. Im 100% sure i didnt have any minute solder bridges, i would have caught any earlier as that is my first method for troubleshooting.

 Apparently, the flux residu (spelling?) from the solder was extremely liquidy (spelling?) and did not dry quick if at all. I realized this after i got a spare board and did some soldering to measure resistance of the flux (which there was none), and realized that after around 10 minutes, the flux still had not dried. I never had this problem before as the previous solder i used had flux that dried and hardened instantly, unlike this one. The liquidy flux i guess was causing shorts between all of the pins.

 Thanks for the tip on using alcohol, ill go over to walgreens tomorrow and pick up a couple bottles along with cellulose sponge.

 thanks guys

 -ivan c


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## Sovkiller

Quote:


 _Originally posted by eyevancsu _
*Thanks for the quick replies. Im 100% sure i didnt have any minute solder bridges, i would have caught any earlier as that is my first method for troubleshooting.

 Apparently, the flux residu (spelling?) from the solder was extremely liquidy (spelling?) and did not dry quick if at all. I realized this after i got a spare board and did some soldering to measure resistance of the flux (which there was none), and realized that after around 10 minutes, the flux still had not dried. I never had this problem before as the previous solder i used had flux that dried and hardened instantly, unlike this one. The liquidy flux i guess was causing shorts between all of the pins.

 Thanks for the tip on using alcohol, ill go over to walgreens tomorrow and pick up a couple bottles along with cellulose sponge.

 thanks guys

 -ivan c * 
 

Hey Walgreens only carried 91% not 99%, if you can get any Drug Emporium, they do carry the 99% , even though 91% should be enough....


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## tangent

Quote:


 I just got in a pound of 63/37 kester .025" solder 
 

Which type? 331 is conductive. As for the others, I'd only risk leaving type 245 flux on the board, as it's the no-clean type. The others _can_ usually be left on the board, but sometimes this causes problems. If you carbonize the flux, it will be conductive. If you trap dirt in the flux, it can be conductive. 

 Even subtler, the flux changes the dielectric constant between two solder points, thus changing the parasitic capacitance. I've had boards where this problem caused oscillation, which went away when I cleaned the board.

  Quote:


 soaking the stuff you build in 99% isopropyl for about a half hour, then dab in between traces/components with a paintbrush (removing any remaining residue) and dry the board using a fan or something. I've heard this procedure recommended to clean off the flux & other surface contaminants. 
 

If you're using professional PCBs and you fill most or all of the holes, you don't need the soaking. Instead, pour a bit of the alcohol into a small dish, dip a stiff-bristled brush into it and scrub the solder side of the board, while trying to prevent the sullied alcohol from getting on the component side of the board. Then use compressed air to blow the sullied alcohol off the board. Repeat until done. I use a stiff-bristled toothbrush for this, but if you're paranoid about static you should use a hogs-hair brush, which you can get from electronics supply places. Mouser has them, in the part of the catalog where the solder and such are.

 With perfboard and PCBs with lots of unfilled holes, you usually end up contaminating the component side of the board: sullied alcohol gets through the holes, evaporates and leaves behind a thin layer of flux. Then what you need to do is drench the board and either scrub at it or soak it so most of the alcohol stays liquid while you blow it off. If there isn't enough alcohol, it evaporates instead of rolling off the board, leaving behind the flux. Even when you drench or soak the board, you'll need to repeat the cleaning except on the smallest boards.

  Quote:


 acetone will clean the flux residues 
 

Yes, and it will also eat some plastics. Acetone is a heavy hammer best left unwielded most of the time.

  Quote:


 residu (spelling?) 
 

Flux isn't a residue, it's "supposed" to be there. The unwanted white stuff left behind when you use impure alcohol is a residue.

  Quote:


 91% should be enough.... 
 

I tend to doubt that. Most of that 9% will be water, but a fraction of that fraction will be impurities. With 99% alcohol (which is usually 99.x% in fact, where x > 0) the fraction of a fraction is truly too small to worry about.


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## Sovkiller

Impurities in alcohol, you scare me, it is supposed to be sterile, and I'm assuming also that he will leave the board to dry completelly, anyway 99% is better but harder to find.....
 BTW the acetone will eat the plastic of the components on the other side of the board, not on the solder side if you use a Qtip to clean the flux, there should be no problems...


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## tangent

Quote:


 it is supposed to be sterile 
 

Calcium is sterile. I still don't want it on my board.

  Quote:


 99% is better but harder to find..... 
 

Probably most of us have imported parts, or placed special orders with odd distributors, or participated in group buys for obsolete or parts without small-volume distributors. Getting 99% alcohol isn't nearly as hard as finding many of the parts we use.

  Quote:


 if you use a Qtip to clean the flux, 
 

I don't have that much free time...


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## Demolition

Quote:


 _Originally posted by Sovkiller _
*anyway 99% is better but harder to find.....* 
 

 Actually, it's not that hard to find. All of my local electronics supply houses sell MG Chemicals' 99.953% anhydrous isopropyl alcohol. I bought a gallon for $20 CDN (~$15 US). Check the distributor list at MG Chemicals to find someone who sells the stuff in your state/province/country.

 D.


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## eyevancsu

Quote:


 Which type? 331 is conductive. As for the others, I'd only risk leaving type 245 flux on the board, as it's the no-clean type. 
 

I just checked the solder and its the 331 type, i didnt bother to check which one i chose before ordering. Is this a bad type, or should i go for the 245?



 Ill go to cvs and eckerds to look for that 99% alcohol, or fry's and see if they have it. If not, ill take your advice Demolition and search MG.

 Thanks

 -ivan


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## tangent

Quote:


 Is this a bad type 
 

Bad, no. The downside obviously is that you can't leave it on the board even temporarily. The upside is that type 331 flux is water-soluble, so it's easier to clean off. You should use distilled water rather than tap water, but that's still cheaper and easier to get than 99% alcohol.

  Quote:


 should i go for the 245? 
 

Personally, I use type 44, since that's the generic standard for electronics. I almost never leave flux on my boards, so the 245 doesn't have any attraction for me.

  Quote:


 ill take your advice Demolition and search MG. 
 

I believe DigiKey and Mouser carry the MG Chemicals line, plus others. MG is known for their board-etching systems, so anywhere you'd buy that stuff, they should also have the alcohol.


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## Sovkiller

Quote:


 _Originally posted by tangent _
*I believe DigiKey and Mouser carry the MG Chemicals line, plus others. MG is known for their board-etching systems, so anywhere you'd buy that stuff, they should also have the alcohol. * 
 

Yep, but 99% alcohol at those places sells for about 20 times their regular price on Drug Emporium, there is just 99 cents a bottle, in other places, sometimes over 20.00 the same amount or even less....The last time I checked it was about 16.00 something an small bottle...


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## tangent

Quote:


 on Drug Emporium 
 

You mean this place?

  Quote:


 The last time I checked it was about 16.00 something an small bottle... 
 

$12.10/gal 99.8% anhydrous

$15.75/gal cubitainer with spigot, 99.8%


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## Sovkiller

Quote:


 _Originally posted by tangent _
*You mean this place?

$12.10/gal 99.8% anhydrous

$15.75/gal cubitainer with spigot, 99.8% * 
 

Yep, unfortunatelly this was the place, they passed away about a year ago, I thought it was only in NJ, but it seems that it was all over the country....shame they had good prices for everything related with health, maybe that was why they passed away....but I still have a few bottles from them though....And I'm talking of about 10.00 a gallon, or less, (they used to sell the pint for 99 cents, at 8 pints a gallon....)

 Wow those yours are good prices, but take a look here:

 Same size as mine, and same brand as yours: this is what I would called an alcoholic rip off, 9 times the price of that pharmacy....


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## Demolition

Quote:


 _Originally posted by Sovkiller _
*Same size as mine, and same brand as yours: this is what I would called an alcoholic rip off, 9 times the price of that pharmacy.... * 
 

 Geez, that works out to be more than $77 US per gallon! 
	

	
	
		
		

		
			





 Quite the ripoff there.

 As I mentioned earlier, the MG Chemicals 99.953% stuff sells for about $15 US per gallon. That's a bargain price for that level of purity.

 D.


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