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Electronics Forum / Electronics / November 2008de-flux pcb or not?
What are peoples ideas on cleaning flux from boards after hand soldering? In particular 511 crystal & 362 rosin lead/tin solders from multicore. Places I've worked have had different attitudes. Any arguments for/against? I've heard a lot of "it looks like sh@t" but in most cases it doesn't matter does it? "K Ludger" > What are peoples ideas on cleaning flux from boards after hand soldering? > In particular 511 crystal & 362 rosin lead/tin solders from multicore. > Places I've worked have had different attitudes. Any arguments > for/against? I've heard a lot of "it looks like sh@t" but in most cases it > doesn't matter does it? ** Generally it does not matter - but sometimes it does. Ordinary ( non acid) solder flux is non corrosive and non conductive WHILE the surface remains hard and shiny. However, if the surface becomes damaged, scratched or broken - then it will absorb moisture from the air and become very conductive, very corrosive and so very harmful to circuit operation. So the " Clint Eastwood Criterion " has to be applied. The one about punks and luck ...... BTW I have seen valuable equipment written off simply because the makers had NOT de-fluxed the PCB before installing all the op-amp ICs in sockets. ...... Phil > "K Ludger" >> [quoted text clipped - 5 lines] > > ** Generally it does not matter - but sometimes it does. Agreed > Ordinary ( non acid) solder flux is non corrosive and non conductive WHILE > the surface remains hard and shiny. [quoted text clipped - 11 lines] > I have seen valuable equipment written off simply because the makers had > NOT de-fluxed the PCB before installing all the op-amp ICs in sockets. Because? - corrosive flux? humid usage environment? > ...... Phil "K Ludger" > "Phil Allison" >>> [quoted text clipped - 25 lines] > > Because? - corrosive flux? humid usage environment? ** Because the DIL sockets had flux coated over them prior to IC nsertion - that is what wave or flow soldering does. Then the IC pins punctured the normally impervious coating on the flux. Then, the flux absorbed lotsa water out of the air. Then the whole device ( a dual 1/3 oct. graphic equaliser made by Phonic of Taiwan ) became ridded with DC leakage current flowing from DC supply pins to adjacent input pins. Result = massive " popcorn noise" in the output . Useless and uneconomic to repair. Fuckwits. ..... Phil > What are peoples ideas on cleaning flux from boards after hand soldering? In > particular 511 crystal & 362 rosin lead/tin solders from multicore. Places > I've worked have had different attitudes. Any arguments for/against? I've > heard a lot of "it looks like sh@t" but in most cases it doesn't matter does > it? We had a batch of boards manufactured with "fluxless solder". Or, it doesn't need flux cleaning after the wave solder stage. At least 90% of our boards would not function till we cleaned them, properly. Ended up sending what's left of the batch back so they can fix their stuffup. That was the first time we've seen this type of fluxless solder being used, (and last time we wanted to know about it) and now demand the boards are cleaned regardless of their process.  SignatureLinux Registered User # 302622 <http://counter.li.org> >> What are peoples ideas on cleaning flux from boards after hand soldering? >> In [quoted text clipped - 19 lines] > (and last time we wanted to know about it) and now demand the boards are > cleaned regardless of their process. Was there anything sensitive about the board John - high gain integrators, very low currents??? > Was there anything sensitive about the board John - high gain integrators, > very low currents??? 60dB gain for one thing, some filtering, analogue switching and the rest was digital (past the A/D stages of course). Oddly enough, we only really noticed the problem with the digital boards, we never got to testing the analogue section because of that. And this isn't seriously high speed either, 8051 based CPUs that were clocked lower than what the CPUs were rated to save power (can't remember exactly how fast though, this was a while back). I do remember they didn't go past about 6-7Mhz. The CPU PLCC through-hole sockets were especially troublesome, where cleaning of the socket pins was required, and in some cases, removal of the socket, clean underneath and re-solder back in again. Not happy Jan. SignatureLinux Registered User # 302622 <http://counter.li.org> >> Was there anything sensitive about the board John - high gain >> integrators, [quoted text clipped - 22 lines] > > Not happy Jan. I've had similar experience with PLCC sockets, they can be a bitch to track down initially. >What are peoples ideas on cleaning flux from boards after hand soldering? In >particular 511 crystal & 362 rosin lead/tin solders from multicore. Places >I've worked have had different attitudes. Any arguments for/against? I've >heard a lot of "it looks like sh@t" but in most cases it doesn't matter does >it? Clean the boards, especially if you have high impedance areas. Ensure that your cleaning materials are clean as well. Do no allow fluxes to remain on component bodies like smd caps (0603, 0805, 1206), etc. If you have flux and dc across a cap, and a humid atmosphere, over time you will get deposition across the surface of the cap, leading to lower impedance across the component and possibly affecting circuit operation. >>What are peoples ideas on cleaning flux from boards after hand soldering? >>In [quoted text clipped - 13 lines] > to lower impedance > across the component and possibly affecting circuit operation. What do you/others use for cleaning? I generally clean with IPA, sometimes metho and sometimes spot rinsing with distilled water. The IPA wash I usually repeat a few times to get rid of the flux salts from between SOIC pads etc. I tried some "citrus" based wash years ago but found it quicke and easier to just use IPA. > What do you/others use for cleaning? > > I generally clean with IPA, sometimes metho and sometimes spot rinsing with > distilled water. The IPA wash I usually repeat a few times to get rid of the > flux salts from between SOIC pads etc. I tried some "citrus" based wash > years ago but found it quicke and easier to just use IPA. IPA alone. As you do, sometimes twice over, first to loosen/dissolve, second to flush that mixture off. And it evaporates faster too, where I can shake it off, let evaporate for a few minutes and I'm ready for testing again. Works well. I never liked metho, it didn't really do a good enough job because it was watered down, and the additives leaves streaks when you're using it for general cleaning. And I didn't want to keep too many different chemicals where I didn't have to. SignatureLinux Registered User # 302622 <http://counter.li.org> > I never liked metho, it didn't really do a good enough job because it was > watered down, and the additives leaves streaks when you're using it for > general cleaning. And I didn't want to keep too many different chemicals > where I didn't have to. Funny thing about metho: Most brands used, Recochem comes to mind are 96% ethanol with water and methylating chemicals as the balance 4% work fine for dissolving flux, but when you use 96% pure non methylated lab ehtanol it just doesn't seem to work at all. It seems the additives make all the difference in my experience. I do have to use a detergent wash and an IR bake afterwards to get a stain free flux removal. >> I never liked metho, it didn't really do a good enough job because it >> was [quoted text clipped - 10 lines] > I do have to use a detergent wash and an IR bake afterwards to get a > stain free flux removal. Know of anywhere cheaper for the IPA than Altronics at $20 for 2L? cheers > Know of anywhere cheaper for the IPA than Altronics at $20 for 2L? > cheers I'd suggest ringing around various cleaning supplies and chemical shops: I think it's used in aluminium cleaner formulations. I used to buy it from a small fibreglass supplies shop for $12 for 2L if you brought your own container. >>>What are peoples ideas on cleaning flux from boards after hand soldering? >>>In [quoted text clipped - 20 lines] >flux salts from between SOIC pads etc. I tried some "citrus" based wash >years ago but found it quicke and easier to just use IPA. I use metho and a 1" soft bristled paint brush. That's because I'm too tight to waste IPA if I don't need to. John |
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