APDS-9006-020 (516-1718-1-ND) has an interesting package design. Unlike a typical component where the solder terminals are on the bottom, these ones are on the top! Why? Broadcom calls this a “Reverse Mount” chip LED package in the datasheet. That being said, if the sensor faces the board, how is it supposed to intake any light?
Appendix Information
This is another reason to keep reading in a datasheet. There is important design information found in the appendix on pages 10-12. The PCBA is supposed to have an aperture window opening cut out and filled in with some polycarbonate material with a smooth surface finish. This is to ensure the best performance. My best guess is that the sensor needs a specific area to be effective and avoid being overexposed that could saturate and cause error in the final application. This design needs to be accounted for before selecting a part in this instance.
Part Category Note
The part category that this is found in cannot account for reverse mounted and “standard” mounted parts. This is still classified as a 1206 metric part in the system. All other parts with the same size will not describe if it is reverse mounted, so it is best to check the datasheets for this detail.