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I've found myself having to solder a bunch of XGL6060 and XGL4040 inductors lately, which have to be reflowed as there's no way to get a soldering iron to the pads underneath the chips. I don't have a reflow oven, but I do have a hot air rework station.

The problem is that the part tends to get blown around by the airflow unless held in place, and it's quite difficult to hold the part in place while also moving the hot air gun around all sides of it. The mass of the part is too high for the solder's surface tension to pull it into position, too. I usually have to try multiple times to get each inductor soldered, because my hand with the tweezers slips and drops the part.

Obviously the proper way to do this is to use a reflow oven, but are there adhesives or anything that can be used to hold the part in place without needing to hold it manually? Or is this simply not a soldering method that's usable for this kind of thing?

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  • \$\begingroup\$ Glue is quite often used. \$\endgroup\$
    – Andy aka
    Commented Oct 4, 2022 at 15:03
  • \$\begingroup\$ @Andyaka Is there a specific type of glue? I've looked in the past for "surface-mount glue" and "pcb glue" and been unable to find anything. \$\endgroup\$
    – Hearth
    Commented Oct 4, 2022 at 15:04
  • \$\begingroup\$ Are you using a purpose-built hot air tool or something else? For those big parts I would suggest a preheat to at least 100-150°C. Usually the solder paste is sticky enough this isn't an issue, even with much smaller parts. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Oct 4, 2022 at 20:15
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    \$\begingroup\$ @Hearth I've used a dot of 5-minute epoxy to keep components in place during soldering. I also second Spehro's suggestion about pre-heating. This simple hot plate from Target on the lowest setting does a good enough pre-heating job. \$\endgroup\$
    – Nick Alexeev
    Commented Oct 4, 2022 at 21:45
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    \$\begingroup\$ @SpehroPefhany It's a purpose-built hot air tool. Not a super high quality one but it does the job--controlled temperature and airflow. \$\endgroup\$
    – Hearth
    Commented Oct 4, 2022 at 23:54

3 Answers 3

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Building off of Andy's comment, I would think that some type of silicone adhesive or flexible epoxy would work well. Maybe even look at flexible liquid engine gasket? It's made for automotive use, but it seems like anything flexible made for high temperatures would be a good fit.

However, if it were me, I would get a reflow oven setup. My work doesn't build enough boards to make it worth us getting a nice reflow oven, but a toaster oven actually works quite well and it's what I've been using for about a year now. I got a high-watt convection model from Target. All you do is set it to the highest temperature, put in the board, watch for the solder to start flowing, wait for 30 seconds or so, and then turn off the oven and open the door. There are lots of great tutorials out there on how to do it, and you don't have to modify it with special controls if you don't want. Works really well for the $50 it costs, and I haven't had a board fail on me yet due to the process. Every once and a while I'll put on too much solder paste and it will cause solder bridges, but that's a different issue. The oven itself works great.

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These two inductor look quite large compared to small resistors like a 0603 or 0402 and those resistors don't get "blown away" by the hot air rework station unless the air setting is too high. Perhaps you should experiment with lower air flow settings. Keep an eye on the temperature as you lower the air flow. It takes more time to reach the desired temperature at lower air flow. You should also be using solder paste. Solder paste is sticky enough to keep the components in place so the hot air rework station won't move them. You may want to look into a hot plate if the the board is too big.

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  • \$\begingroup\$ I am using solder paste. The moment the flux in the paste fully liquefies, the part goes sliding all over the place; while 0603 and 0402 parts can stay in place with surface tension and adhesion, something this large can't be pulled into place that way. \$\endgroup\$
    – Hearth
    Commented Oct 4, 2022 at 23:55
  • \$\begingroup\$ With high air settings you can easily blow away much larger parts than those. \$\endgroup\$
    – Lundin
    Commented Oct 5, 2022 at 9:52
  • \$\begingroup\$ @Heart Try putting less solder paste on the inductor pads. \$\endgroup\$
    – Rodo
    Commented Oct 5, 2022 at 16:25
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The problem is that the part tends to get blown around by the airflow unless held in place, and it's quite difficult to hold the part in place while also moving the hot air gun around all sides of it.

Usually a nozzle that is roughly the size of the IC is a good way to get hot air to only where it is needed (and also at low speed if possible to avoid heating and moving components around the IC). You can even use a holder to hold the air gun in place and then poke the IC with tweezers.

Most air stations will come with a few nozzles and have more available enter image description here Source: https://www.adafruit.com/product/3596

However, it can still be difficult to heat inductors sufficiently, in the past I've used a PCB holder to also use a hot air gun on the bottom and top sides of the board if the inductors have large power planes connected to their terminals. Another thing I've done is get an IR rework station to heat the board, even heating the bottom of the board to 60 or 70C can make it so much easier to heat a part because the ambient temp of the board is much higher and so heat wicks away into the board at a slower pace.

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  • \$\begingroup\$ I've considered getting an IR preheat system. I'm not sure if I can convince my boss that the expense is worth it, though. Someone linked a $28 hot plate up above that might help a bit; I could afford to get that on my own dime if necessary (though I can't imagine they'd balk at that price, unlike some of the IR stations I've seen). \$\endgroup\$
    – Hearth
    Commented Oct 4, 2022 at 23:57
  • \$\begingroup\$ Unfortunately nozzle selection can't really help that much when working with a large part like this. Should I try to get the entire part heated? I had thought it would be enough to aim the airflow underneath the inductor to heat the pads on the bottom (though of course heat goes up into the coil from there). \$\endgroup\$
    – Hearth
    Commented Oct 4, 2022 at 23:59

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