How to read datasheets
Which is the common way to handle the large exposed pad on the bottom of a QFN package?
- ASoldering it makes it prone to cracking from thermal stress, so provide no land on the board and leave it floating above the board
- BTo keep it electrically isolated, cover the corresponding area of the board with solder resist and do not connect it
- CProvide a land on the board, solder the pad, connect it to the specified potential (often GND) and conduct heat away through thermal vias
Show answer and explanation
Answer: C. Provide a land on the board, solder the pad, connect it to the specified potential (often GND) and conduct heat away through thermal vias
The exposed pad is the underside of the die pad, on which the chip is mounted, exposed outside the package; it is the main path for heat into the board. The datasheet θJA value is typically measured with this pad soldered to the board and connected to inner-layer planes through thermal vias, and leaving it unsoldered greatly degrades heat dissipation. The recommended land pattern may also show the stencil aperture divided into segments to adjust the solder volume and prevent voids and component lifting. Follow the datasheet for the potential to connect it to.