BMM350 custom dev board problems

[errorhuhn]

Dear Bosch-Sensor Experts!

We would like to integrate the BMM350 in our product design, so after a few tests with the OEM dev-board I designed a custom version with integrated voltage regulator to provide 1,8V VDD out of 3,3V total supply! Unfortunatelly, my custom dev-boards don't work (Most of the time I get no successfull I2C acknowledgement from the Sensor, there were some random moments it worked but not reproducable).

Some Details:

BMM350 VDDIO = 3,3V from STM32 Supply

BMM350 VDD = 1,8V from voltage regulator

ADSEL = HIGH (I checked that, its different to the standard from the OEM dev boards)

Digital Pullups = 1kOhm

I don't see any mistakes in the schematic, what do you think, is a problem during soldering process more likely? Its hard to check because everything is so small, but soldering optically seems pretty okay I think... Do you have any other tipps for troubleshooting?

Best regards

Erik

[errorhuhn]

Okay, case solved, soldering was the problem. I accidentally used padsize D=0.21mm instead of the recommended D=0.25mm so there were contact errors.

I solved the issue by adding some flux to the chip, heat it for ~45s with hot air station (270°C) and tapped slightly with the tip of the hot air station on the chip to gain some pressure to get contact between all solder balls and pads. 

It's not the prettiest solution, but it gets the job done.

Best regards

Erik

[BSTRobin]

Hi errorhuhn,

Good news.
To avoid potential risk in the hardware design, you can also refer to the suggestions in this link(https://community.bosch-sensortec.com/t5/MEMS-sensors-forum/BMM350-Selection-criteria-for-the-CRST-c...) to check whether the external capacitor meets the requirements?