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liquid flux + lead-free temp oven = killed silkscreen?


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hey guys, an interesting thing happened when i build my board last night, i put a drop of liquid flux on the board to encourage the solder to flow on the little micro bga package.  when i took my board out of the oven and cleaned the flux residue off, the silk screening just wiped away where the flux had been.... 

 

I switched from a gel type to a liquid type flux recently, and didn't have this problem with the gel type.

 

the other explanation is this silkscreen was somehow defective, but i doubt that because the other boards from this set of 3 did just fine with the same conditions (allbeit with the gel)

 

anyway what do you guys think?

 

what is odd is the base rosin type is the same in both CAS#

 

the liquid flux has

"modified" Rosin: CAS#8050-09-7

ethanol: CAS#64-17-5

2-butanol: CAS#78-92-2

 

the gel flux has

WW Gum Rosin: CAS#8050-09-7

Diethylene Glycol Dibutyl: CAS#112-73-2

Dymerex Rosin CAS#65997-05-9

 

its obviously more noticeable on the back where the flux flowed under the board, cause it completely removed half my logo

post-7036-0-62989300-1363462541_thumb.jpg

post-7036-0-75409200-1363462833_thumb.jpg

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Evidently, the ethanol or 2-butanol is the culprit.  Isopropanol is frequently used to clean boards, but it is hard to say if one of these other alcohols is causing the problems.  Ethanol is a two-carbon alcohol, Propanol 3, Butanol 4.  You can buy ethanol easily, and try that, but my guess is the butanol is the culprit.  Butanol and larger alcohols are often used in degreasing agents.

 

One option to find denatured ethanol is to find it at a pharmacy store (sometimes sold as "Ethyl Rubbing Alcohol").  Another option is to buy some high-proof grain alcohol (sometimes sold as "Everclear").

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whats funny is the liquid flux is listed on that list on mouser...  MG Chemicals 835-100ml.  its data sheet says its designed for lead and lead free soldering.

 

other than the female header, the board was cleaned, that staining is in the silkscreen and won't come off. the rest of the residue was gone in those pictures.

the female header was soldered by hand after I cleaned the other stuff off

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whats funny is the liquid flux is listed on that list on mouser...  MG Chemicals 835-100ml.  its data sheet says its designed for lead and lead free soldering.

Sure, but the red-residue stuff is what I usually see on electrical soldering, not so much electronic soldering.

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