hot air rework temps

parts-man73

Lately I've purchased a nice hot air rework station. I've been searching around the internet for recommendations on a proper temperature and airflow setting, but I haven't found any obvious references.

I know that different brands and compositions of the solder paste do vary and the reflow temperature is found on the datasheet. I guess my question is, should the rework station be set right at the datasheet reflow temp? slightly higher?

I found the following video www.youtube.com/watch?v=MOEHstgaVLM&feature=related and the demonstrator set his station to 390, which seems much to hot, compared to the reflow temps on the datasheets that I have looked at. Although in the video, he is removing components, not attaching.

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Brian

uController.com - home of SpinStudio - the modular Development system for the Propeller

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James Long

Brian,

Your question is sort of like asking how far will a bow and arrow shoot. There are many factors that will contribute to how high you set the rework station.

First the the setting on the output of air. The more air, the larger area will be heated.

Second, is your board and it's design. Does it have copper pours or just traces.

Third, what kind of part are you trying to attach, a DDpack takes more heat that a 44 pin QFP (more mass).

I hate to say it, but for doing a whole board, a rework station is not the way to go. Taking parts off or replacing them, I whole heartedly agree, but reflowing, a toaster is a better purchase.

Just for reference though, you may think 390 is a bit hot, but remember he must soak the board, traces, and part with heat. Also the board is going to be acting like heat sink while he is doing this (removing heat). I personally think 390C (I'm assuming the station in question is measured in C) is too hot. It is hot enough to delaminate a PCB. But it is a double edged sword with putting parts on the first time. You want the process to happen fast enough that the flux is still present. If you take too long, the flux will have "flashed off" and will not wet the parts out well. Too much heat and you will blister the board, or melt the part.

I make it sound terribly hard, when it is not. Just be aware of the possibilities.

I wish I could be more help, but doing parts with a rework station is a little different for each person. The great thing, if you do not get it attached the first go around, add a little flux, more heat and try again. Do be aware there are some packages out there that do not like being heated multiple times (mostly some crystals). Practice with the passives first, they are usually the most forgiving.

Just for reference: for leaded solder I start out at about 250C. With lead-free about 300C. These are subject to your unit and it's precision. I also go up or down as needed. (But I only use the station for rework)

James L

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James L
Partner/Designer

Lil Brother SMT Assembly Services

Erik Friesen

The quick and dirty method -

Set the air low enough so that the parts don't blow off the board. I use the big nozzle most of the time.

I would set it at around 475. If your parts (caps especially) or board start turning color you know you are too hot. I have yet to damage a chip from being too hot. I would say it is more important to control the heat and cool speed.

parts-man73

I knew there was no "Magic number" but rather a starting point, from which I adjust to taste. You've both given good insight. Thank you both.

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Brian

uController.com - home of SpinStudio - the modular Development system for the Propeller

PropNIC - Add ethernet ability to your Propeller! PropJoy - Plug in a joystick and play some games!

SD card Adapter - mass storage for the masses Audio/Video adapter add composite video and sound to your Proto Board