Ultra detailed engineering render of a custom DIY smartphone mainboard, black FR4 PCB, 4-layer PCB, STM32H750 microcontroller in LQFP package, FS-MCore-A7670C 4G LTE module, USB-C charging connector, TP4056 protection charging module footprint, 5V boost converter, PAM8403 audio amplifier, INMP441 I2S microphone, ESP32-CAM connector, vibration motor connector, JST battery connector, Raspberry Pi style camera connector, female 2.54mm TFT 4.0 inch SPI header for ILI9488 display, side mounted power switch, power button, volume buttons, gold ENIG pads, realistic PCB traces, vias, mounting holes, compact smartphone layout 135x70mm, top view, professional PCB CAD render, KiCad style, highly accurate electronic component placement, photorealistic, no fantasy, black solder mask, white silkscreen, clean engineering design.