Is SMD soldering possible with heat gun?

Projects
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Hello,

I’m currently working on my first PCB for a personnal project (air quality monitor board) and I’m having some beginner’s questions so first please pardon my ignorance :stuck_out_tongue:

I’m wondering if it is possible to solder 3 sensors with the tools I have.

I have a Soldering station and some soldering gel and I’m would like to solder the following sensors:

The problems I’m facing:

  • Bosch BME688 has pads below the sensor, they are not visible when the component is placed on the PCB. The datasheet recommend to solder it using reflow but I don’t have a oven so I would like to know if it’s possible to solder it with the heat gun ? The datasheet is saying that we should not heat the sensor above 260°C (not longer than 20-40 secondes) and I suppose it’s not enough to solder it with my heat gun. Do you think it’s impossible with my heat gun/soldering iron ? If yes, how can we know when it’s correctly soldered if we can’t see the result ?
  • The SGP41 has a pad under the sensor and the datasheet is also recommending to solder it using reflow technique. It has around the same limit in high temps.
  • What would you recommend to solder the TSL2591 ? Is it better with the heat gun or the soldering iron ?
  • JLCPCB is the manufacturer I choose to print my PCB, If the problems mentioned above can’t be solve with the tools I have I’m thinking to use their assembly service but there is also a problem here because the reflow at a temperature of 255°C which is higher than what Bosch and Sensirion recommend for the reflow soldering. They also don’t mention the amount of time in which the sensor will be exposed to that temperature. Am I overthinking or is it also not possible ? JLCPCB assembly capabilities are visible here

Luckily the rest is not that hard to solder ^^ It’s simple capacitors, resistors and other things bigger with no pads at the bottom :stuck_out_tongue:
Also if you think I should buy some extra tools don’t hesitate to tell me, I saw some persons having a heating plate to heat up the pcb first, I’m not sure if it’s needed. I also think I will probably need a good magnifying glass so if you have good recommendations I would be happy to hear them :slight_smile:

Thank you for the time you spend on reading my noob problems :smiley:

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I suspect the velocity of the hot air will make components move.

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I used to solder BGAs using a heat gun: BGA Soldering With A Paint Stripper And Stopwatch | Hackaday

If this is a personal project, then my recommendation is to try the simplest thing and see if it works. Then adjust as necessary.

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In my book, the 255°C of JLCPCB is lower than the 260°C maximum specified by Bosch for BME688. I wouldn’t worry about this, if JLCPCB say they can solder a component, let them do it and don’t worry about how they do it.

While it is possible to solder BGA with a heat gun, it is hard and i personally wouldn’t do it. If i where in your place, i would either try to search for an alternative with something like a TQFP or a other package that can be soldered with a soldering iron or use a assembly service.

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You have chosen an ambitious task for the first time. I’m playing with electronic for 55 years but I have never tried to solder such elements myself.

Never had it but it should make a task easier.
I have read that someone used iron (used as a hot table) to reflow soldering and others used toaster. Not sure if I use right name - something that what you want tost you put inside horizontally and you not close the toster. I think it was something like:

As everything it needs some tests to get experience but I have read that people do it at home.

I have also read that amateur solution to solder ICs thermal pad is to make a PTH hole under it and solder it from backside.

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What are you using for solder for your surface mount parts ? unless I’m mistaken that gel is just flux ? getting enough solder paste, but not too much, is really down to a stencil for such small components.

Then your hot air gun might work in combination with some heat from the bottom, from perhaps a clothes iron.

As others have said . . . it’s not an easy thing to cut your teeth on.

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Maybe with enough air the board will move along with the components? :laughing:

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there are a few ways to solder SMD conponents “by hand”, the already mentioned toaster works, you also could put the PCB on one of the heating surfaces of your stove and heat it until the solder paste melts and hot air guns also work but need practice.

but as others already said: for your first project I would recommend using a population service. they know what they are doing and won’t kill your components with to high temperatures no worries. you will face enough other hardships with your first design so don’t put extra burden on you with not that simple hand soldering.

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I have been building boards for 50 years and have not been brave enough to try soldering a BGA package yet. Having seen yield problems needing 100% xray on these using a proper reflow oven, it’s not easy

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It can be done and there are many youtube examples about soldering SMT stuff. From a (fine) sand filled skilled or hot plate to hot air guns or modified toaster ovens. I think I like the modified toaster oven best.

Tiny and delicate stuff like that Bosch sensor is not a great way to start though. You will need some skill and experience, both to have a decent chance to solder it reliably, and for keeping the sensor intact.

For starters it is very likely better to buy sensors like this on a breakout board.

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I’ve tried a handful of methods but was never satisfied enough. About the best approach was Conductive Epoxy… cleaner, simple, no melted chips, parts…etc

There may be other similar products better tailored for glueing parts to PCB’s as I bought this years ago to conclude my curiosity about using SMD mounted part…

Call me ‘Old-School’ but, I stick with THT.

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I haven’t done those sensor specifically, but I have done a couple of small IC and modules with pad on the bottom. for that I bought a cheap chinese hot plate:

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And I use solder paste with low melting temperature (around 140°)

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it works well for hand soldering, you need to be extra careful to have some kind of alignment marks on your PCB, with the pads on the bottom, is difficult to know how well are positioning your component on top of the solder paste, it is not extremely critical, as the component will be pulled/pushed in place due to the surface tension, however, that only work up to a point.

I also tried with a hot air gun, I did not like it, the very small component flew away never to be found and it is difficult to know the know if the melting process has been done or not (again, you cannot check it visually)

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That was my first plan but I was scared to kill the sensor with that amount of heat. I’ll probably give it a try anyway :smiley:

As they don’t mention the time at that temperature it could damage the sensor, that’s why I was not sure.

Ah, I thought I was just missing some basic skills but it seems more difficult that I thought ^^ Thank you for your feedback :slight_smile:

I think I will try try the method with the heat gun from above, as I don’t have a toaster that I can use for that. I will check if I can modify something I have at home :stuck_out_tongue:

Could be good hint, I’ll investigate that as well. But as the BME688 has 8 pads to solders on the bottom (pads are 0,4mm), I don’t think it will be feasible.

It is soldering paste (or cream they called it)

That could be a good idea too, I don’t have one at home but I can ask the one from a friend/parent for some time :stuck_out_tongue:

I’ll probably try multiple approach, paying JLCPCB to solder some themself, try some with the heat gun from above, maybe try with a hole, why not the technique with the clothes iron. I’ll see what works for me.

Good idea :slight_smile:

I quickly checked and it seems to cost around 50-60usd, do you think it would work with a clothes iron or the stove would work too ?

I imagine haha I will have to build kind of prison around the soldering desk to ensure it does not go away :joy:

So to summarize, those are the techniques mentionned:

  • Heat gun from above (maybe too much heat for the sensor)
  • Pay the manufacturer to do it themself :rofl:
  • Heating from below the pcb (clothe iron / stove / heating plate / sand) with low melting temp solder paste

Let’s vote :laughing:

Thank you very much for all your suggestions, it helps me a lot !

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Not from above, but from below, you basically place your PCB on top of it and let the solder melt:

There are lots of DIY Kits to turn small ovens or irons to reflow oven/ hot plate, many videos about it too in YT. I believe using the iron directly will work, maybe measure the maximum temperature first to know what setting you should use (Silk or Cotton? :smile: ).

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I think you will be disappointed. Only few people actually do solder BGA by hand and they first learn other skills. It is your decision but i would suggest you to search for breakout board, such as bme688 breakout board and you find boards with the BME688 already soldered (by machine) and some large THT-Pads (often 2.54mm grid) you can solder by hand.

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The problem with heating from below using a hot plate to reflow will melt EVERYTHING on the board, and if you have double sided placement the hot plate option is obviously out. It is relatively easy to hand solder small BGA and smt components by hand. Many QFP packages have a thermal pad on their undersides which must be soldered down even though their legs are exposed. I have a 2 heat gun setup for doing this. The idea is to heat the board from the underside to about 160C with the big heat gun (My Makita has temperature control which makes this dead easy and safe) then use my temperature controlled hot air rework station with an appropriately sized nozzle to bring just the component of interest up to temperature. This really isn’t hard to do, just takes a little practice. The hot air rework machines from China are reasonably inexpensive so even a hobbyist can afford one. My Makita heat gun was about NT$3000 (a little over $100US). Preheating the board is essential to getting reflow to work properly. Applying solder paste by hand is difficult to say the least. Best to just pre-tin the pads under the part with the right amount of solder, and be careful not to put too much on the thermal pad under a TQFP if that’s what you are soldering down. The liquid tacky flux works pretty well too and is essential when working with lead free solders since those oxidize very quickly when heated.

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Thank you I corrected my previous post !

Thank you will definitely check that ^^

Wow thank you for those precious hints ! I have only one hot air rework station, do you think it would be possible to replace the hot gun from below with something like the stove or the clothe iron ? The idea would be to just preheat the pcb with the stoven and apply the heat on the sensor from above as you said.

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The problem with the stove or clothes iron technique is the difficulty in controlling the temperature. If you have a meter with a thermocouple probe you can try the stove technique but DON’T try it without some way to measure the surface temperature of the skillet or whatever you are heating. It’s WAY easier to control the temperature of hot air and a lot safer for the board. If you want to reflow an entire board I’d go the modified toaster oven route since you can heat from the bottom as well as the top, plus the thermal mass in the toaster oven is much less (makes temp easier to control) than the skillet technique. You can achieve a reflow profile pretty much like a professional reflow oven if you do a good enough job modifying your toaster oven.

I used a paint stripping heat gun before I got the Makita to preheat the undersides of my boards. The key there was using a thermocouple probe and adjusting the position of the heat gun so I could mix in some ambient air to control the temperature at the underside of the board. Takes some fiddling but can be made to work. Downside is a lot of excess heat put into your workspace so you need to work deftly to get the job done quickly.

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I have recently closed several off-topic threads, so I feel obliged to close this one, too. Sorry about that.

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