As this is the first time I have ever done hot air work, I really don't feel qualified to answer, but...
The chip I was replacing was an SOIC-8 package closely surrounded by numerous smaller components that I was very wary of accidentally moving. Initially I used the smallest nozzle (about 2.5mm) to try to aim the air just at the pins but it was too restrictive so I went up to a nozzle around 5mm diameter using 370degC with airflow set on 5 (out of 8) Once I got the chip off, there was plenty of solder remaining on the pads so I only added some flux, positioned the new chip and started heating. Only took about 15 seconds for the solder to start to melt then I held the heat for a little longer. What I have read recently is that the two major conditions to adjust heating for are chip size and thermal mass of the board. As the number of layers goes up the heating requirement goes up massively. On Wed, Dec 19, 2018 at 9:54 AM Terry Kennedy <[email protected]> wrote: > On Tuesday, December 18, 2018 at 7:29:36 PM UTC-5, gregebert wrote: >> >> Paul - Can you post some details about the hot-air soldering/reflow you >> did ? >> >> I'm soldering my SMT devices manually by hand because my casual >> experimenting with a heat-gun got bubbled PCBs and very hot (and probably >> damaged) ICs. >> > > When doing assembly (as opposed to re-work) a few parts at a time, the > idea is to pre-heat the board (usually via IR to the underside) to a > bit below the melting point of the solder paste you're using, then use the > air gun to melt the solder paste you put under the parts you're > soldering. That way you don't need a ton of very hot air coming out of the > nozzle, since that would end up overheating the component before the board > got hot enough for the paste to stick to the traces. Re-work is a bit more > of a mixed bag, since you may have components on both sides of the board > and the parts you're trying to remove are usually larger than the ones you > want to leave in place - people starting out tend to blow things like > resistors / caps off the board while heating the part to be removed. Even > with the exact matching nozzle on the air gun, that air has to go > somewhere. Pre-heat also helps with this, though you'll likely want a lower > temperature so any parts on the underside aren't at risk. > > Preheating also helps with some through-hole rework - I do a lot of > work on Cisco boards (8 to 12-layer) and things like power supply caps > are connected to interior layers that are pretty slab-like. And Cisco > doesn't seem to like to use relief areas arround those inner-layer holes > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/ce4bb062-1a8d-4f3d-a46a-52854172e664%40googlegroups.com > <https://groups.google.com/d/msgid/neonixie-l/ce4bb062-1a8d-4f3d-a46a-52854172e664%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CAB6XHa8O3DNiB1pBQBBezroX1O9PD8xhO94EV4tGW%2BJX4FqNjA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
