What are Footprints and Land Patterns

4. Land Patterns

4.2. Provided Land Pattern Accuracy

Land-Pattern Double-Check

Creating land-patterns is one of the more tedious aspects of electrical engineering.  But sometimes you just have to sit down and do it.  It's also worth noting that you will often find mistakes in the land patterns you find in online-libraries, which should further motivate you to create your own libraries of custom parts.  As an example, the land-pattern for the BNO055 we sourced for this design was originally identical in size and shape to the footprint of the BNO055.  

Page 102 of Bosch-Sensortec's BNO055 datasheet (bst-bno055-ds000.pdf) provides a somewhat intimidating amount of information about the footprint dimensions.  But there is absolutely no information about a suggested land pattern name, no information on how to go about creating a land pattern, or where on the Bosch website an appropriate land-pattern might be found.

Footprint dimensions for BNO055

The engineers at Bosch apparently expect PCB designers to take the information from this diagram and use the equations from IPC-7351 to design or create an appropriate pattern.  

I imagine whoever made the land pattern that Bob and I initially found was so focused on deciphering the information from the datasheet that they missed the fact the land pattern wasn't present at all, so they created a 1:1 copy.

While the centerline spacing for the rows and columns of pads will be a 1:1 copy, land pads are always bigger than part pads.