Capacitive Electrode for Concrete Slipform
Publicada el 2026-07-14
Descripción de la oferta
# FastForm Capacitive Sensor Electrode — PCB Design & Order Brief --- ## Overview I need a **very simple 2-layer PCB** designed and manufactured. Two variants, 5 boards each. **This board has no components, no traces, no schematic, and no routing.** It is four copper rectangles and three vias. Someone competent with KiCad should complete the layout in under an hour. **Important context so the design decisions make sense:** this is not a normal circuit board. It is a **capacitive sensor electrode** that will be immersed in wet concrete. The **solder mask is a functional dielectric layer**, not a cosmetic finish. Several instructions below will look unusual for a PCB — please follow them exactly rather than applying normal PCB conventions. --- ## Deliverables 1. **KiCad 7 or 8 source files** (I need these for future revisions) 2. **Gerber files** (RS-274X) and **Excellon drill files** 3. **Order placed on my behalf** with JLCPCB (or PCBWay if cheaper), shipped to me 4. **Order confirmation + tracking number** 5. **One question answered by the fab** — see "Question for the fab" below --- ## Board specification — common to both variants | Parameter | Value | |---|---| | Outline | **100 × 100 mm** square | | Layers | **2** | | Substrate | FR4, **1.6 mm** | | Copper | **1 oz (35 µm)**, both sides | | Impedance control | **No** | | Controlled dielectric | **No** | | Castellations / edge plating | **No** | --- ## VARIANT 1 — `FF-CAP-100` (guarded) ### Front copper — F.Cu Two **electrically isolated** filled zones, both centred on the board: | Zone | Geometry | |---|---| | **ACTIVE PLATE** | Filled square, **80 × 80 mm**, centred | | **GUARD RING** | Filled square, outer **94 × 94 mm**, with an **82 × 82 mm** cutout — producing a **uniform 1.0 mm gap** between plate and ring on all four sides | Result: a solid 80 mm plate, a 1 mm bare-FR4 gap all around it, then a 6 mm-wide guard ring, then 3 mm of bare FR4 to the board edge. ### ⚠ CRITICAL — solder mask on the front face > **Both front zones must be FULLY COVERED BY SOLDER MASK.** > **There must be NO mask apertures and NO exposed copper anywhere on the front face.** > > The solder mask is the sensor's dielectric layer. If any copper is exposed on the front, the board is **unusable** — it will short directly into the wet concrete. This is the single most important instruction in this brief. Normal PCB practice would expose copper somewhere; here, do not. ### Back copper — B.Cu - **GROUND PLANE** — filled zone, **94 × 94 mm**, centred - Solder-mask covered **except** at the three pads below ### Connections — back side, one corner Three solder pads, **2.5 mm diameter**, mask-opened, **5 mm apart**, silkscreen-labelled: | Pad | Net | Connection | |---|---|---| | **ACT** | Active | Via to the front ACTIVE plate. **⚠ Place this via at the geometric CENTRE of the 80 × 80 mm plate**, not at its edge. | | **GRD** | Guard | Via to the front GUARD ring. Via position anywhere convenient within the ring. | | **SHD** | Shield | Connects to the back GROUND PLANE. | **All three nets must be electrically isolated from one another.** No connection between plate, guard, and ground plane anywhere on the board. ### Silkscreen - Back side: board name **`FF-CAP-100`** - Back side: the three pad labels **ACT**, **GRD**, **SHD** - Front side: **nothing** (keep the sensing face clean) --- ## VARIANT 2 — `FF-CAP-100-NG` (unguarded control) **Identical to Variant 1 in every respect, except the guard ring is omitted.** - Front: **ACTIVE PLATE only** (80 × 80 mm, centred, solder-mask covered) - No guard ring, no GRD pad (or leave the pad present but unconnected — your choice, just tell me which) - Back: ground plane and ACT / SHD pads as before - Silkscreen name: **`FF-CAP-100-NG`** *This is a deliberate experimental control. It exists so the guard ring's effect can be measured rather than assumed. Please do not "helpfully" add the guard back in.* --- ## Manufacturing order Please order from **JLCPCB** (or PCBWay if cheaper) using **exactly** these options: | Option | Setting | |---|---| | Quantity | **5 of each variant** (10 boards total) | | Layers | 2 | | Dimensions | 100 × 100 mm | | PCB thickness | **1.6 mm** | | Copper weight | **1 oz** | | Surface finish | **HASL, lead-free** | | Solder mask colour | **Green** | | Silkscreen | White | | **Conformal coating** | **NO — leave uncoated** | | Panelisation | None | | Gold fingers / impedance control | No | **Please confirm total cost with me before placing the order.** Expect roughly **US$30–60** for both variants including shipping to Australia. --- ## Question for the fab — please ask and report back > **"What is the nominal solder mask thickness, in microns?"** I need this number. This board uses the solder mask as a functional dielectric, and its thickness directly determines the sensor's coupling capacitance. Any value between **15–40 µm** is acceptable — I simply need to know which. If the fab won't provide it, that's not fatal; just tell me they declined. --- ## Summary of the unusual requirements Because these will look wrong to an experienced PCB designer, here they are in one place: 1. **No exposed copper on the front face.** Solder mask over everything. Yes, really. 2. **The ACT via goes in the centre of the plate**, not at the edge. 3. **Three isolated nets**, no ground stitching between them. 4. **Variant 2 deliberately omits the guard ring.** This is intentional. 5. **No conformal coating.** (I know it's a wet application — I want the first run uncoated as a calculable baseline.) 6. **No front silkscreen.** If anything here seems like a mistake, please ask me before "correcting" it.
Skills
Fuente original: freelancer