IMU - 9 DOF LSM09DSO Chip Mounting on carrier bd ?

[brianb00]

Hi Bill ?

ST Micro has a specific set of instructions regarding the soldering (reflow) on circuit boards for the LSM09DSO 9DOF sensor. They also have similar rules for other sensors. Does AdaFruit follow those rules ? For example, no feed through-s beneath the chip, no traces beneath the chip, basically nothing that would touch the package surface such that strain could result between the package and the solder pads. They also have rules for layout so that the board won't warp at temperature due to copper versus FRP size changes.

I am using the 9DOF module currently and am wondering about how they might fare in production with regards to offsets of the sensors.

Regards,

Brian Boschma

[adafruit_support_bill]

Looking at the back of the board there is a conspicuous bare area under the chip. I will check with the designers regarding other layout considerations.

[brianb00]

Hi, It is the area directly under the chip, beneath the chip and the board that should be kept clear of any feature.

Thanks for checking into this.

[adafruit2]

you can see the layout here
https://learn.adafruit.com/adafruit-lsm ... -pcb-print
there is no trace or copper underneath the chip

[brianb00]

The layout looks pretty good. One area of concern, the top row of contacts are all connected very closely to a copper plane, this is quite different density than the other three sides. That could potentially warp during the reflow and cool down process putting strain on the package. The other area that ST specs is the height of the solder stencil, resulting in a certain height of solder paste. This is to again prevent asymmetric pressure on the chip.

Sorry to be so questioning but I am considering using the Adafruit board for small volume production and want to avoid big variations in sensor offsets.

Thanks,
Brian

[Franklin97355]

If this board, as designed does not fit your parameters perhaps it is not the board you should be using. You could always design the chip into the board you are planning to build. That way you have total control of the placement and routing of the lands.

[brianb00]

Hi Frank,

Yes I could design in the product myself. Sometimes time to market can be enhanced by using a suppliers parts. My comments were simply to make you aware of something ADAFRUIT might consider to enhance the product quality.

Brian

[Franklin97355]

My comments were simply to make you aware of something ADAFRUIT might consider to enhance the product quality.

No problems with that. Adafruit always welcomes constructive suggestions.

[brianb00]

I followed your advice and did my own board layout. The resulting board keeps the chip in spec, regarding rate gyro offset. I have confirmed this on 6 proto boards. The 1 adafruit board I have is out of spec by about 2X what is shown in the data sheet. If you are considering rev-ing your board you might follow the ST Micro layout suggestions very closely. Admittedly a sample of one unit from Adafruit is much of a statistical sample.

Regards,
Brian