Electronics > Beginners
Hot air soldering, what am I doing wrong?
iMo:
Even the gel flux liquidize with hot air, therefore you have to find a balance between airflow speed and its temperature such the flux is not blown off the pads/pins. That requires some experimenting. I even had a small table I made with air speed, temperature and distance from the pcb, trying to mimic a profile. The pcb temperature is important as well, you have to avoid cooling it from the bottom side. Tricky.
wraper:
--- Quote from: imo on November 16, 2019, 10:31:44 pm ---Even the gel flux liquidize with hot air, therefore you have to find a balance between airflow speed and its temperature such the flux is not blown off the pads/pins. That requires some experimenting. I even had a small table I made with air speed, temperature and distance from the pcb, trying to mimic a profile. The pcb temperature is important as well, you have to avoid cooling it from the bottom side. Tricky.
--- End quote ---
Liquid flux evaporates, does not stay liquid. Liquid flux is mostly solvent with a little bit of actual flux. Also tacky fluxes have an order of magnitude higher work time.
TheHolyHorse:
--- Quote from: TomS_ on November 16, 2019, 09:40:54 pm ---
--- Quote from: TheHolyHorse on November 16, 2019, 07:27:04 pm ---I heated the board so that the solder on the pads was molten when I placed the chip on the board so every thing should be hot and toasty.
--- End quote ---
Hmm. So you didnt have the chip on the board at the same time? Have you tried with the chip on the board while heating it up as well, so its leads also get cleaned by the flux, and also so the parts heat up at the same rate? Placing a cold part in to hot solder doesnt sound like a great idea.
I also wonder if maybe you need more solder on your pads? If there isnt enough, perhaps it doesnt have anything to "float" on in order for surface tension to align it.
--- End quote ---
Yeah since it didn't align for me and I lost patience I just gave up and left the chip not aligned properly but stuck. I later added more flux and heated it again hoping it would suck it in place.
TheHolyHorse:
--- Quote from: wraper on November 16, 2019, 10:46:10 pm ---
--- Quote from: imo on November 16, 2019, 10:31:44 pm ---Even the gel flux liquidize with hot air, therefore you have to find a balance between airflow speed and its temperature such the flux is not blown off the pads/pins. That requires some experimenting. I even had a small table I made with air speed, temperature and distance from the pcb, trying to mimic a profile. The pcb temperature is important as well, you have to avoid cooling it from the bottom side. Tricky.
--- End quote ---
Liquid flux evaporates, does not stay liquid. Liquid flux is mostly solvent with a little bit of actual flux. Also tacky fluxes have an order of magnitude higher work time.
--- End quote ---
So for hot air I should get some better flux, preferably some gel stuff? I'll do some research on that.
wraper:
--- Quote from: TheHolyHorse on November 16, 2019, 11:01:21 pm ---So for hot air I should get some better flux, preferably some gel stuff? I'll do some research on that.
--- End quote ---
Anything other than tacky/gel flux will be spent before solder melts.
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