The Microchip ATMEGA168P-20AU is an 8-bit AVR RISC microcontroller from the ATmega family, running at 20 MHz and packing 16 KB of Flash program memory (organized 8K x 16) plus 1K x 8 SRAM and 512 x 8 EEPROM.
Peripheral set and I/O — what you can connect without extra glue
That covers the common sensor buses (I²C for temperature/humidity, SPI for ADCs or displays) and a debug/programming UART without external level shifters, since the I/O is 5 V tolerant.
Package and footprint — 32-TQFP with 7x7 mm body
The exposed pad is not present on this package variant, so thermal dissipation relies on the leadframe and board copper. The 0.8 mm pitch is hand-solderable with care but reflow is the production method. No special keep-out zones beyond the usual TQFP land pattern.