The question is simple. I only ever seem to find a soldering-related hot air gun on a machine dubbed a “rework station” and the only reference I can find to using hot air to solder SMD components is on a few YouTube videos. Is a hot air gun on a soldering station really only designed for desoldering and some people tend to, I guess, “misuse” it for freshly soldering parts?
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2\$\begingroup\$ I was using it for heat shrinks.... \$\endgroup\$– Eugene Sh.Commented Apr 9, 2019 at 15:37
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\$\begingroup\$ Well if you are desoldering, you are likely to solder it back. You can reflow the whole board again (stressful for components and not viable for some hand soldered connectors) or just solder it back with hot air (assuming QFN, BGA, etc). So, if you consider desoldering a proper use, why would re-soldering be a "misuse"? \$\endgroup\$– Wesley LeeCommented Apr 9, 2019 at 15:44
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\$\begingroup\$ I guess only because I would expect just as many references to using a soldering heat gun for soldering as there are for desoldering, which I don’t seem to see. Just because a staple remover can remove staples, there’s no reason to assume that it can also apply staples. I’m not contending that it is a misuse, I just want clarification that soldering with hot air is a common use. \$\endgroup\$– Adam SperryCommented Apr 9, 2019 at 15:51
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2 Answers
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It's not really a misuse to use a hot air hand rework station for soldering parts, but it would be uneconomical to solder whole boards with it in a production setting. Getting consistent, high-yield results when soldering hundreds of SMT parts by reflow requires careful control of the time-temperature profile, which is very difficult to achieve with a hot air gun. It also involves exposing various components to repeated hot-cold cycles as you move the gun around the board, which is punishing treatment for them - most are only rated for 3 or so reflow cycles.
For prototyping purposes, if you don't want to use a proper reflow oven or the cheapie toaster oven equivalent, the best bet is probably to solder all parts with leads using an iron and a drag-soldering or flood-then-wick technique. Use the hot air gun only for the bottom-terminated components, and accept that your yield isn't going to be 100%.
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\$\begingroup\$ Thank you for the nuanced treatment of your answer \$\endgroup\$ Commented Apr 9, 2019 at 15:55
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\$\begingroup\$ There's nothing wrong with a cheapie toaster oven as long as the temperatures are controlled. I use an old Sears 4-element, 1500W toaster oven, monitor the temperatures with a probe into a multimeter, and time it on smart phone. Process works very well for Kester EP256 63/37 leader solder which has been applied using a mylar, or metal (larger boards where the mylar moves too much) stencil. I bought a couple of these, and just refill them now from a 150g tub cmlsupply.com/… (finished off a 500g tub) \$\endgroup\$ Commented Apr 9, 2019 at 19:31
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A rework station is different than a "hot air gun" or "heat gun," which are similar but don't have precise temperature controls. A rework or reflow gun/station can be used in any application where heat is required at a precise temperature. You will see some desoldering, resoldering, or just directly soldering a fresh component. Things like solder paste combined with existing solder masks, make it fairly easy to apply paste to an SMD component, apply some hot air (set to the temp solder temp) and the melted solder will wick to the board and SMD contacts. Aside from that, it has many other uses (like heat shrink). It's a tool just like any other, though don't fall for everything looking like a nail kind of approach.
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\$\begingroup\$ In our old plant with 6 lines we used controlled humidity =50% minimum to improve convection Quartz heater reflow but with forced air and hot base plate you can minimize added hot air from spreading to keep out zones. There are many nozzles to also restrict air flow over IC to reduce time reach liquidus temp after while ramping up base plate temperature to mimic suggested profile. \$\endgroup\$– D.A.S.Commented Apr 9, 2019 at 16:31