Hello everyone, I need some advice.
I am making custom PCBs for a project of mine. It’s basically for a little remotely controlled robot using little DC motors. I chose the Seeed Studio XIAO ESP32C3 as the uC since it has inbuilt wifi/bt, 3.3V regulator that I can use to power the motors (can source up to 700mA) and lipo charging management (the robots will run on battery). As you can see from here, the microcontroller is surface mounted and the pads for the battery are on the bottom layer. Same story goes for the thermal pad of the microcontroller and the thermal pad of the motor driver (datasheet). I have worked with SMD components in the past and can solder them by hand, but I have never worked with SMD components that have thermal pads on the bottom layer. My question is: how to manage (route?) them? My PCB is 2-layer and I was planning on having both layers filled with a ground plane. Do I just connect thermal pads to the ground plane and call it a day? Wouldn’t that make the components hard to solder with hot air? Do I make an isolated polygon that only acts as a thermal pad?
Speaking of soldering is even hot air the way to go in this case? My PCB has components on both sides, and I was planning on ordering stencils together with the boards and using solder paste, placing the components and then using hot air to solder the components in place. I thought a hot plate would be better but I don’t have access to one and I don’t know how that works with components on both sides.
I attached some photos of the PCB in Kicad, and here’s the git repo. If it is of any help, I’m planning of having them manifactured by JLCPCB. It is also my first time using KiCad, so go easy on me :)
Thanks!
I disagree with his otherwise great advice: make the two middle planes GND, route your power and signals on the outermost layers.
The closer your gnd plane is to your signal or power lines, the lower the inductance and the increased resistance to emi. Otherwise any noise on the vcc plane is separated from the gnd plane by about a mm, vs being less than 0.2mm away from the gnd planes if they’re the two middle layers.
The copper is also usually thicker on the outer layers and you have access to atmospheric cooling.
The copper is thicker on OSHPark’s outer layers, but its thinner (!!!) on DKRed’s outer layers.
Just an FYI in case other people here are USA-based and want to use USA-based PCB makers. Yeah, that’s right. DKRed has thin 0.5 oz outer layer copper and 1oz inner-layer copper. I’m guessing DKRed is aiming at the Gnd-signal-signal-Gnd style boards… while OSHPark’s 4-layer stackup is better for signal-gnd-gnd-signal.