| | | | | I am looking for anyone who has converted over to VOC Free flux. I need some info on any problems, etc. that you might have had. | | | | | | | | | | Please E-mail me at wes.ruggles@vickers-systems.com or call at (513) 494-5229 | | | | | | | | | | Thanks | | | | | Wes Ruggles | | | | | | | | | Wes, | | | | | | | | There's a couple of postings in the SMTNet Library on VOC-Free flux evaluations and on spray fluxer evaluations, as well. | | | | | | | | Chrys | | | | | | | | | | My own evaluations on VOC-Frees have begun!! Here were my initial observations: | | | | | | I "dropped in" the Alpha (nr310b) last Wednesday (May 5), and guess what - it dramatically reduced our solder skips on 0603's! We had a run of roughly 400 boards and got only 3 or 4 skips (probably glue related). | | | | | | A few things that HAVE changed, however include: | | | | | | 1.) Our flux spray station daily maintenance requirements�.there's lots of "dried up" residue all over the spray station, and more liquid deposit inside the spray tank�.and I'll bet a million bucks it's because the new flux is water-based, and of course, water just don't evaporate as fast as alcohol | | | | | | Did the same thing happen with anyones else's spray station also?? | | | | | | 2.) Our top-side PCB temps. are in the 220 - 230 ballpark. Bottom-side is about the same. The board literally SIZZLES upon exit - and yes, I did here some snackling, crackling, and popping upon contact with the wave. One of our operators complained of fumes upon exit also. | | | | | | Should I reprofile to get higher top-side temps. to avoid sizzling? my original intention was NOT to have to reprofile anything. | | | | | | | | | Anyone else experience anything similar??? Chrys....help me please!! | | | | | | Other than that, the "good" things that've changed were better solderability on hard-to-solder stuff like 0603's. | | | | | | | | | | | Here in the environmentally-conscious state of New Jersey, we've been VOC-free since the early nineties. So there's always been water in the drip pan of the fluxer, for pretty much as far back as anyone can remember. | | | | When we put the top two VOC-frees (Heraeus SURF11 and Alpha NR 310B) head to head, the operators made a list of important criteria. Ease of cleanup was one of them; smell of boards at the exit was another. It seems that the Alpha cleaned up relatively easily and had the least obnoxious smell, especailly when compared to the Kester 970 that we had been using. I think these issues are all part of the game with the VOC-frees, you just gotta find the lesser of the evils, ya know? | | | | The crust (or fluxcicles, as we call them) really do wipe off esily with the Alpha. Other products required hot water or alcohol, and even scotch-brite to break the crust. Weekly ceanup of the fluxer chassis went from about an hour down to five or ten minutes. We were psyched. If you're going from 2 minutes up to 10 minutes, I can see where that would be a bummer. | | | | Snap, crackle, pop at the wave definitely means the board is hitting it wet. One option is to deposit less flux from the sprayer. The range for the 310 is to deposit 500 to 1500 ug/in^2. We're running right about 550. This stuff is nicely active, so you don't really need a whole lot. The other option (if you're looking for solderability and not VOC-free) is to try the Alpha Lonco 65. It's pretty close to the 310 in terms of thermal stability and performance, but it's alcohol based. | | | | Sizzling upon exit sounds like there's moisture in the boards themselves. Any leftover water from the flux gets evaporated at the wave. | | | | Reprofiling everything would not be fun. Unless you have a co-op , summer intern, technician, or good operator to delegate it to! You would have to lower preheat temps and slow the conveyor to get more time in the preheat zones. Then you'd have to modify your wave height to get the right contact at the lower conveyor speed. Yuck. Sounds like a can o'worms. I'd really work to try for less flux deposition with good solderability. Then I'd see if all my assemblies were crackling at wave contact or just a few. And the ones that are crackling, I'd look for solderballing and determine if it's really a big, bad issue worth reprofiling over. Unless of course, I had that summer intern coming in June... ;-) | | | If the board is 220-230 F when it enters the wave, how is it possible that the flux carrier (water) is still on the board when water turns to steam at 212 F? I have always wondered how, if your board follows the correct pre-heat recommendations, it would be possible for any water to be present at the wave. Unless, of course, the board was absolutely saturated and the water was boiling when it hit the wave. What gives? | | Ryan Jennens | TelGen Corporation | Hey Ryan,
Great question. If the top of the board is 220F, how can there still be water on the bottom if it boils at 212F? Great answer - if the water was still boiling when it hits the wave. Remember back to thermodynamics class (anurism time!) At std pressures, water never gets hotter than 212. It just keeps boiling at 212, no matter how hot your heat source is. The excess energy is given off as steam, but it doesn't all go to steam right away. The more energy you put into it, the faster the water will be converted to steam.
If you don't believe me, put a pot of water on the stove. Get it boiling, and take the temp. 212. Turn the flame all the way up so its rapidly boiling. Still 212. Turn the flame low enough to just maintain the boil. Still 212. The only difference between the high and low flame is that the high flame makes steam faster - the higher input of energy causes a faster evaporation rate. So the high flame will boil the pot dry faster than the low flame, but the liquid in the pot will always be 212 at sea level.
Which brings me to a tangential rambling on the most important thing I learned in six years of engineering school. Ice water chills beer faster than ice alone in the cooler. If there's ice in water, even if the ice is 10 degrees, the water never gets colder than 32F. And the ice cube will never get warmer than 32F. They'll reach equilibrium at the phase change and stay there, with the warmer water (and beer) giving up energy to melt the ice. Couple that with the thin film heat transfer coeficient of water (as compared to air), and your beer goes from 80F to 32F in ten minutes flat. The single most important thing I learned. And by far the most highly utilized, to date. Almost made suffering through thermo and heat worth the effort.
Okay, no more Friday afternoon ramblings. The water is still boiling when it hits the wave. It is also trapped in the pores of the solder mask, under components, and in holes. And the snap, crackle, pop, is the rapid vaporization from the sudden surge of energy that the hot solder puts into it.
Sorry for the ramblings,
Chrys
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