Add BME280 to MotionMote

[MojaveTom]

I'm planning to replace the Z-Wave room environment sensors in my home with MotionMote with BME280.  This combination will give me the information I would like.

Unfortunately, Felix is out of MotionMote with BME280, so I bought some BME280 from Mouser and would like to add them to MotionMotes that don't have them.  I noticed that the MotionMote R3 BME280 pads have some solder build up.  I mistakenly thought that if I put flux on the pads and position a BME280 carefully, then heat with a hot air gun, that I could solder the BME280 onto the board.  That didn't work.

Does anyone have any suggestions on how to do this?

[Felix]

Well it's going to be tricky for sure, I would not learn SMD soldering on a BME280.
It's however doable.
Hot air is your best bet and flux is your friend in this case.

FWIW -since I made the MotionMotes I changed the BME280 pads to be a little longer which makes soldering them or rework much easier.

[MojaveTom]

Here's my latest plan.

Start with new MotionMote board.
Clean any solder off the BME280 pads.
Put a tiny dab of solder paste on the pads.
Carefully place the new 280 on the board.
Heat the whole board on an electric hot plate to 80%? of the melting point of the solder used to solder the existing components.
Heat the 280 with hot air till the solder melts.

So questions:
Is this a reasonable approach?
If so, to what temperature do I set the hot plate?
How do I know when the 280 is properly soldered?

Thanks.

Tom

[MojaveTom]

Felix,

What solder do you use when you make the boards?  I'm trying to figure out a temperature for adding the BME280.

Thanks,
Tom

[LukaQ]

Don't complicate too much, use what you have or what you can get. Reflow until soldered

[Felix]

For SMD rework of this kind, hot air, liquid flux and a lot of care.

[MojaveTom]

I found a "low temperature" stable solder paste:  https://www.digikey.com/product-detail/en/chip-quik-inc/TS391LT/TS391LT-ND/7802220.  I used an Xacto knife and a microscope to put the paste on the BME280 pads, then carefully placed the BME.  Heated till the solder melted on a hot plate.  Amazingly, it seems to work.

My plan is to make a stencil out of sheet protector plastic, and a guide for placing the BME.  The stencil is going to be a lot of careful Xacto knife cutting.  The placement guide is to avoid squishing the BME all around when placing it.