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I was looking at using the raytac MDBT50Q-UATMS radio module for a personal project. I am still investigating exactly which module I will use, but I expect it to be similar to this one.

enter image description here

Looking at the recommened solder pad layout, we can see that this is a no-lead part, and the pads are located under the part. For a regular microchip one could hand solder this using some solder paste and a hot air gun. The problem is that this part is not a chip, but rather a whole PCB with lots of little parts on it.

From experience I would say that this isn't going to be 10 seconds of light air. I would need to hit it with a lot of air for quite a while to get the solder on the bottom to melt onto the pads. Pre heating the host PCB can help. But if I shoot that much air at it, there is a real possibility of little parts moving around which would make the module unusable.

enter image description here

So, the question then becomes, what method can be used to solder a small SMD radio module (that has lots of little parts on it) to a PCB without a reflow oven?

This particular module has an RF shield over a lot of the parts, and that helps. But I am interested in a general answer that works with any kind of SMD module with small exposed parts on the top side.

One option is to find a SMD module that has uses castellated edges for the connections (avoiding hidden pads altogether). I could then just solder each connection with a soldering iron as normal. But looking around I have been unable to find a module in that format that also has the range I want and a connection for an external antenna (it's going in a metal box so the antenna must be external, and it's going outside pretty far away so it needs long range).

My first guess would be to design the host PCB with a little clearance around the module. Then cut and bend a small piece of 30-gauge scrap sheet metal into a small box (like 12 x 17 x 10 mm) that fits around the module. Finally drill a small hole in the side to stick in a thermocouple. I could then shoot hot air at the outside of the box and the inside would heat up like it was in an oven. But since there is no airflow (other than convection inside the box), no parts get blown around.

I hope someone else has some good answers for this.

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    \$\begingroup\$ How about a hot plate? \$\endgroup\$
    – Bryan
    Dec 3, 2022 at 7:16
  • \$\begingroup\$ Heater plate, hot air solder and kapton tape to prevent other components. But preferably invest in a (cheap) reflow oven. \$\endgroup\$
    – RemyHx
    Dec 3, 2022 at 7:24
  • \$\begingroup\$ I have removed modules like that with hot air before (never tried installing one). The shield usually gets detached. I think some type of toaster oven or hobby reflow oven is the best bet. \$\endgroup\$
    – user57037
    Dec 3, 2022 at 7:31
  • \$\begingroup\$ @RemyHx I looked around a bit at cheap ovens, but most of them were either 220V or had high current requirements (25~30A). All of the outlets in my garage are 120V and rated for 20A or less, so I would likely be faced with adding a breaker on my panel, running wires for the outlet, and dealing with all the county permitting paperwork (or else hiring an electrician to do all that). Either way, it doesn't look like it's going to be cheap, not even counting the cost of the oven. \$\endgroup\$
    – user4574
    Dec 3, 2022 at 22:13
  • \$\begingroup\$ You can probably use a toaster oven with a convection fan. You may have to experiment a bit to find the right time and temperature. \$\endgroup\$
    – user57037
    Dec 4, 2022 at 1:57

2 Answers 2

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For a one-off personal project I would suggest purchasing the inexpensive MDBT50Q-DB-ATMS demo board.

Or you could try a dedicated toaster oven or skillet approach on an unpopulated board with fresh solder paste but I'd not be particularly optimistic about it being reliable. A domestic oven would probably work if you're careful about removing it when toasted but it's potentially unhealthy to mix food with whatever comes off such an operation.

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  • \$\begingroup\$ Your idea of using the demo board can work. I see that the MDBT50Q-DB-ATMS demo board is available from several sellers for $18.95. It also looks like the board has 3.3V power and a UART interface with flow control on J10 which can be used to interface to a host PCB with a microcontroller. They stuck some critical control signals (UART PD, FLASH DEFALUT, and RESET) on J11. Having to use both J10 and J11 is a bit annoying since I now have to use two connectors, but they don't give the relative X/Y positions or positional tolerances between the two. \$\endgroup\$
    – user4574
    Dec 4, 2022 at 2:57
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for a one-off Flip it upside down and solder jumper wires between the module and the board.

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  • \$\begingroup\$ I have done something similar to this approach with the HOPERF RFM75 module and it worked. The RF performance was good even at several hundred feet distance when I tested it. In that case I put on like 4 inches of wire and hot glued the module to the side of the box and then put a small header on the end of the wires to connect it to the main board. \$\endgroup\$
    – user4574
    Dec 3, 2022 at 22:03

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