How much heat to dial into a rework/hot air station? - Page 1
Forum section: electronics / beginners

author: tcv
author_rank: Contributor
timestamp: September 29, 2013, 12:57:20 am
content: Sooooooo, I bought a hot-air rework station and I'm playing around with a donor HDD PCB. I'm aiming to take off components and maybe put something back on just for practice.It occurred to me really quickly that... well, I don't know what temperature to dial into the rework station. I placed some flux on all the sides of an IC and dialed the rework at 315 and blew air ... and blew and blew ...So, I don't really know what I'm doing. What's a good temp for removing SMD PCB components?

author: Balaur
author_rank: Unknown
timestamp: September 29, 2013, 02:40:28 am
content: Experiment with higher temperatures (350, 380 Celsius) until you get good results.If you have a board with components that you don't care about, use a lot of air with a large diameter nozzle and see how fast the solder is melting. Then experiment with smaller nozzles, air flows and temperatures.PS: Don't use flux when desoldering, it will only shield the solder joint from the hot air.

author: Bored@Work
author_rank: Super Contributor
timestamp: September 29, 2013, 02:42:13 am
content: You have to try it out and practice, practice, practice. The cheap hot-air rework stations don't have calibrated temperature controls, and air speed as well as the nozzle have an impact, too. Oh, and distance from nozzel to component, and how fast you waggle the nozzle around. And environment temperature, preheating, etc.Start with medium air speed, or if you happen to have a rework station with reasonable air-flow adjustment, try 20 l/min air flow for a start.Use a nozzle for the particular package. If you don't have an exact matching nozzle try the next larger one. If you don't have one, use the standard 5mm diameter nozzle for small components, and a large one or no nozzle (22 mm) for large components. Avoid nozzles smaller than e.g. 2 mm for a start, unless you really need to, because they badly affect air flow on cheap stations.Start with 350 deg. If nothing happens or it takes ages, try 375 and then 400 deg.Start with a distance of approx. 2 cm from nozzle to component. If you don't use a special, matching nozzle, e.g. if you just use the 5 mm nozzle, circle around the component. Don't keep blowing on the same spot for a longer time. Even if you use a special matching nozzle, move at least up and down a bit and rotate the nozzle if possible to avoid creating a hot spot (cheap rework stations have the "interesting property" that the heaters don't uniformly heat the air flow, because the heaters aren't mounted exactly centered. If you use a wide nozzle or no nozzle there can be a temperature difference in the output hot air.)

author: tcv
author_rank: Contributor
timestamp: September 29, 2013, 04:28:13 am
content: Thanks to both of you. I had been using a smaller nozzle as I thought it would minimize accidentally melting solder around other components. Eh, but it IS a board I don't care about.I will try higher temps and a larger nozzle.FWIW: I bought the hot air station that was featured in the videos, the one which some people found to be dangerously miswired. (That hasn't happened to me. I am still al

author: amyk
author_rank: Super Contributor
timestamp: September 29, 2013, 11:22:39 am
content: ...and make sure it actually melts solder first, just put a small piece on some heatproof surface and point the gun at it.

author: onlooker
author_rank: Frequent Contributor
timestamp: September 29, 2013, 12:56:09 pm
content: I sometimes place a temperature probe on the part or board under heating to monitor the actual heat up process. This should be a more accurate way to assess if the part is under or over heated.

author: tcv
author_rank: Contributor
timestamp: September 29, 2013, 02:15:38 pm
content: Quote from: amyk on September 29, 2013, 11:22:39 amHmmm... Make sure the temperature I have chosen melts the solder? I don't know that I understand what you mean by "it".

author: tcv
author_rank: Contributor
timestamp: September 29, 2013, 02:18:56 pm
content: Quote from: onlooker on September 29, 2013, 12:56:09 pmActually that's another question I had: I imagine one _can_ damage components with too much heat but how does one know how much heat is too much?

author: onlooker
author_rank: Frequent Contributor
timestamp: September 29, 2013, 04:09:49 pm
content: This is a quote from wikipedia,"A standard guideline is to subtract 5 °C from the maximum temperature that the most vulnerable component can sustain to arrive at the maximum temperature for process. It is important to monitor the process temperature to keep it from exceeding this limit. Additionally, high temperatures (beyond 260 °C) may cause damage to the internal dies of SMT components as well as foster inter-metallic growth."But, when I occasionally have the need to remove parts, I was not really bothered with these and I mostly wanted to do quick jobs by using higher temperatures. I have not seen many damaged parts yet.

author: wraper
author_rank: Unknown
timestamp: September 29, 2013, 07:56:36 pm
content: That's quiet predictable with lead free multilayer board which works like a heatsink. Use higher temperatures or buy preheater which makes soldering a lot more easier.

author: free_electron
author_rank: Super Contributor
timestamp: September 29, 2013, 08:06:01 pm
content: What the hell ? you air temperature should be max about 10 to 20 degrees more than the melting point of the solder used.for lead/tin melting is 183. max 200 degree c for your air flow thenfor leafdfree melting is 220 so max 240.you simpl yneed to wait long enough or increase the flow. you are leaking to much temperature.

author: jaxbird
author_rank: Frequent Contributor
timestamp: September 29, 2013, 08:25:54 pm
content: Quote from: tcv on September 29, 2013, 12:57:20 amI generally set mine at 320C, doesn't mean components will be heated that much (depends on distance and nozzle), but it gives reasonably quick heating and desolder or reflow.

author: Bored@Work
author_rank: Super Contributor
timestamp: September 29, 2013, 08:33:58 pm
content: Quote from: free_electron on September 29, 2013, 08:06:01 pmThe hell is that the displayed temperature and the actually delivered air temperature of these cheap hot-air stations is quite different.

author: tcv
author_rank: Contributor
timestamp: September 29, 2013, 08:41:22 pm
content: Well, since I didn't put together this little HDD PCB, I don't really know what kind of solder was used. However, with the numbers posted, I can get a reasonable idea.I realize I'm doing a lot of flailing, but I guess I have freedom and time to do that right now. No need to be right because others are counting on me or something.Is there any particular time table I should be thinking about? Something like... if it takes over 60 seconds to melt the solder then the temp or airflow is not right. I guess I just need to get back in there and start playing with it some more.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: September 29, 2013, 10:27:57 pm
content: QuoteYes I can vouch for that, my POS hot air station varies day to day. I think it's mainly the pump.

author: wraper
author_rank: Unknown
timestamp: September 30, 2013, 12:18:02 am
content: Quote from: free_electron on September 29, 2013, 08:06:01 pmYou will never melt any solder with such air temperature, at least if station shows correct temperature and air flow is not like a thunderstorm. Only if you use preheater, 30+ degrees above melting point will start to melt solder. Board will never be as hot as air from nozzle. Low temperature without preheater will work only for 1-2 layer boards with low thermal capacity. And I know what I'm saying, I soldered tons of BGA, uBGA, checked actual board and air temperature. Today, for example, reballed underfilled tegra3 and flash/ram combo in HTC one X. Because they were underfilled, I needed to check actual temperature before lifting them from PCB, otherwise I could lift them together with pads.

author: Balaur
author_rank: Unknown
timestamp: September 30, 2013, 06:10:02 pm
content: Quote from: wraper on September 30, 2013, 12:18:02 amHello wraper,Just by curiosity, can I ask what is the typical scenario and motivation to do this kind of stuff? Where you able to find and buy the chips in an affordable and timely manner?Best regards,Dan

author: wraper
author_rank: Unknown
timestamp: September 30, 2013, 10:15:43 pm
content: Motivation was that I bought some broken HTC one X on ebay cheaply. Tegra 3 loses contact with the board on this model after phone is dropped heavily. I reuse original ones. That underfill is a real PITA actually, when you heat one chip that junk expands and damages soldering under surrounding chips.

author: Balaur
author_rank: Unknown
timestamp: October 01, 2013, 12:14:00 am
content: Hi wraper,Thanks for the explanation, much appreciated!Best regards,Dan

author: tcv
author_rank: Contributor
timestamp: October 02, 2013, 02:03:32 am
content: Quote from: wraper on September 30, 2013, 12:18:02 amWhat is this preheater thing?

author: wraper
author_rank: Unknown
timestamp: October 16, 2013, 09:39:00 am
content: Hot air preheater, There is also IR type which is basically hotplate.

author: tcv
author_rank: Contributor
timestamp: October 20, 2013, 12:10:24 am
content: Quote from: wraper on October 16, 2013, 09:39:00 amThanks, Wraper!