> For the complete documentation index, see [llms.txt](https://mujoseph.gitbook.io/mujoseph-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mujoseph.gitbook.io/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design.md). # PCB Design ## General Design Guidelines All PCBs used for the *Emma Mk1* were manufactured by [JLCPCB](https://jlcpcb.com/), including the [*GDT Driver*](/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design/gdt-driver.md)*,* [*Current Sense*](/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design/current-sense.md) and [*Motherboard*](/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design/motherboard.md) PCBs. Special care was taken to choose parts that were available from their [internal parts catalogue](https://jlcpcb.com/parts) to ensure ease of manufacturing. Components that could not be sourced by JLCPCB directly were hand-populated in-house. BOM curation placed a premium on choosing components that were available in easy-to-hand-solder packages (SOIC, TSSOP, etc.) and avoided BGAs and QFNs altogether. Where possible, passive components were sized as 0805 (or larger) since space was not a concern. To assist in rapid prototyping, the standard motherboard-daughterboard approach was used. The motherboard hosts the *STM32G474RE* MCU, and all daughterboards mate to the motherboard via standard 100 mil (2.54 mm) pitch pin headers (GDT Driver PCB), shielded ethernet cable (Current Sense PCB), or a 40-pin ribbon cable (Raspberry Pi 4B). The design allowed modules to be debugged separately and, in the case of the GDT Driver PCBs, iterate through several designs without the need to re-spin the other boards. ### PCB Copper Weight All high-voltage, high-current PCBs were manufactured as 2-layer boards with 4.5 oz copper weight on the outside layers, which was the maximum supported by JLCPCB at the time of manufacture. ## Board-to-Board Interface The high-voltage PCBs that carry the high peak, high $$\frac{dI}{dt}$$ primary current, interface with each other via two M5 screws per electrical net (see image below). The PCB surface areas that contact an adjoining PCB have the solder mask pulled back to provide a high surface area, copper-to-copper contact point in an attempt to provide a low-inductance, high-capacitance interface. The M5 screw pairs, coupled with their respective flat washer, lock washer, and nut, provide the clamping force necessary to ensure that the adjoining PCB's exposed copper areas are making maximal contact. Due to mechanical assembly and manufacturing variabilities, the planar interface will contain small voids in which the copper pours are not perfectly pressed together, increasing the overall impedance of the interface. If necessary, a conductive grease or paste, such as [MG Chemicals' 8463A – Silver Grease](https://mgchemicals.com/products/grease-for-electronics/electrically-conductive-grease/contact-grease/), can help increase the conductive and thermal properties of the interface. Currently, the *Emma Mk1* does not use conductive compounds.

High-voltage PCBs board-to-board interface points. Note that the PCB
exposed copper pours and M5 mounting hardware is not rendered.