PCB Schematic & Layout — STM32 BGA, Ultra-Low-Power Outdoor Battery Device

My partner and I are developing a battery-powered outdoor device (an acoustic sensor for gardens). We've got the full prototype running today across three development boards, and we're now looking for a PCB designer to take it to our first custom board — schematic and layout, leading to 5–10 assembled prototypes. We can arrange fabrication and assembly in the UK ourselves, but if you have a good working relationship with an assembler you trust, we're open to that too. We've done a lot of the groundwork: there's a detailed spec pack (can be shared under NDA) with pin maps for every inter-chip interface, a measured power envelope, memory maps, and requirements with the reasoning attached. All the firmware exists and runs on the bench prototype, and we do our own bring-up — the test infrastructure (SWD headers, UART consoles, a current-sense point) is specified in the spec. The architecture and main part choices are largely decided, so we're looking for is someone to design the board within them. The board, briefly: - STM32N657 (264-ball VFBGA, 0.8 mm pitch — the only BGA) + an STM32U5 (LQFP64) + a pre-certified ESP32-C6 WiFi/BLE module - Octal xSPI NOR + 16-bit xSPI PSRAM — controlled impedance and length matching on these two buses; everything else is low-speed - PDM MEMS microphone (1.8 V domain), bottom port — the acoustic hole goes through the PCB - 3S Li-ion battery pack input, USB-C charging, and a low-quiescent-current buck regulator tree with an LDO post-regulated analog rail and load-switched sub-rails - 6 layers expected, ENIG, ~60 × 90 mm, double-sided assembly. On the BGA fanout (dogbone vs via-in-pad) we'd like your recommendation - It's an outdoor device: −20 to +60 °C operating target, so component temperature ratings matter, and keeping the battery safe in hot sun is one of the things we're thinking hard about Battery life is a key consideration for us. The whole system idles at ~3 mW (measured), and keeping it there on the custom board — regulator selection, quiescent current, light-load behaviour — is a key requirement. One of the deliverables we'll ask for is a predicted per-rail idle-power budget before layout starts. Not everything is decided, and on the open items we'd genuinely value your advice rather than just execution: charger IC selection (it needs to boost from USB-C 5 V to the 3S pack, with temperature-limited charging), the battery connector pinout, the IO voltage plan across the 1.8 V / 3.3 V domains, and the antenna variant on the radio module. These are open decisions we'd want your advice on. Deliverables: schematic + layout native source files (KiCad or Altium — either works; full native sources to us regardless), Gerbers, BOM with alternates, pick-and-place, assembly drawings, board STEP model, the idle-power budget, DFM notes, and a pool of bring-up support hours. IP assigned to us on payment. Please quote fixed-price against the full spec, with your expected timeline. Design work starting from around Sep/October 2026, fab-ready in 4–8 weeks. To apply, please answer these two questions: 1. Tell us about one battery-powered and/or BGA-based board you designed that shipped — what the product was, your specific role, and one design challenge on it. 2. What's the lowest-power device you've designed? Roughly what did it idle at, and what were the one or two design choices that got it there? We're a fairly technical client (software background) and happy to collaborate via written documents and meetings. Happy to answer questions before you propose.