Enclosure Design Guidelines
Parent Document: HARDWARE_OVERVIEW.md
Version: 0.1.0-draft
This document covers enclosure design, materials, manufacturing methods, and tamper-evident features for SimpleGo hardware.
Design Philosophy
Requirements by Tier
| Requirement | Tier 1 | Tier 2 | Tier 3 |
|---|---|---|---|
| Protection | Basic drop/scratch | IP54 splash resistant | IP67 waterproof |
| Tamper Evidence | Optional stickers | Serialized screws | Cryptographic verification |
| Material | 3D printed plastic | CNC aluminum | Potted CNC aluminum |
| Assembly | Snap-fit / screws | Gasket + security screws | Epoxy sealed |
| Cost Target | €5-15 | €80-150 | €150-300 |
Tier 1: 3D Printed Enclosure
Material Options
| Material | Pros | Cons | Use Case |
|---|---|---|---|
| PLA | Easy to print, biodegradable | Brittle, low heat resistance | Prototypes |
| PETG | Stronger, better heat resistance | Slight stringing | Production DIY |
| ABS | Durable, heat resistant | Warping, requires enclosure | Higher quality |
| ASA | UV resistant, durable | Harder to print | Outdoor use |
Recommendation: PETG for DIY production kits
Design Guidelines
┌─────────────────────────────────────────────────────────────┐
│ ENCLOSURE CROSS-SECTION │
├─────────────────────────────────────────────────────────────┤
│ │
│ Wall thickness: 2.0mm minimum │
│ ┌─────────────────────────────────────────────────┐ │
│ │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ │
│ │ ▓ ▓ │ │
│ │ ▓ ┌─────────────────────────────────────┐ ▓ │ │
│ │ ▓ │ PCB │ ▓ │ │
│ │ ▓ │ (with standoffs) │ ▓ │ │
│ │ ▓ └─────────────────────────────────────┘ ▓ │ │
│ │ ▓ ▓ │ │
│ │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ │
│ └─────────────────────────────────────────────────┘ │
│ │
│ PCB standoffs: 3mm height, M2.5 screw bosses │
│ Display cutout: +0.5mm tolerance │
│ Button cutouts: +0.3mm tolerance │
│ │
└─────────────────────────────────────────────────────────────┘
Snap-Fit Design
┌───────────────┐
│ TOP SHELL │
│ │
Snap hook ──────┤► ┌─────┐ │
│ │ │◄───┼── Catch
│ └──┬──┘ │
│ │ │
└──────┼───────┘
│
┌──────┼───────┐
│ │ │
│ ┌──┴──┐ │
Catch ledge ────┤► │ │ │
│ └─────┘ │
│ │
│ BOTTOM SHELL │
└───────────────┘
Hook deflection: 0.5-1.0mm
Hook angle: 30-45°
Minimum 4 snaps for secure closure
Print Settings
Layer height: 0.2mm (0.12mm for fine details)
Infill: 20-30% (gyroid or grid)
Perimeters: 3 minimum
Top/bottom: 4 layers minimum
Supports: Minimize with design orientation
Print orientation: Largest flat surface on bed
Files to Provide
enclosures/tier1/
├── simplego_diy_top.stl
├── simplego_diy_bottom.stl
├── simplego_diy_buttons.stl # Optional button caps
├── simplego_diy.step # For modification
├── simplego_diy.f3d # Fusion 360 source
└── README.md # Print instructions
Tier 2: CNC Aluminum Enclosure
Material Selection
| Alloy | Properties | Use Case |
|---|---|---|
| 6061-T6 | Good machinability, anodizes well | Standard choice |
| 6063-T5 | Better surface finish | Premium appearance |
| 7075-T6 | Highest strength | Maximum durability |
| 5052 | Best corrosion resistance | Marine/outdoor |
Recommendation: 6061-T6 for balance of cost, machinability, and strength
Design for CNC
┌─────────────────────────────────────────────────────────────────┐
│ CNC DESIGN GUIDELINES │
├─────────────────────────────────────────────────────────────────┤
│ │
│ WALL THICKNESS │
│ ───────────────── │
│ Minimum: 1.5mm (2.0mm recommended) │
│ Near features: 2.5mm minimum │
│ │
│ INTERNAL CORNERS │
│ ───────────────── │
│ Minimum radius: Tool diameter / 2 │
│ Recommended: R1.5mm for 3mm end mill │
│ │
│ BAD: GOOD: │
│ ┌────┐ ╭────╮ │
│ │ │ │ │ │
│ │ │ │ │ │
│ └────┘ ╰────╯ │
│ Sharp corner R1.5 radius │
│ │
│ POCKETS │
│ ───────────────── │
│ Maximum depth: 4× tool diameter │
│ Draft angle: 0° acceptable for CNC (not injection molding) │
│ │
│ THREADS │
│ ───────────────── │
│ Use threaded inserts (brass) for frequent assembly │
│ Direct threads: M3 minimum, 2× diameter depth │
│ │
└─────────────────────────────────────────────────────────────────┘
Gasket Design (IP54)
┌─────────────────────────────────────────────────────────────────┐
│ GASKET GROOVE │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Cross-section: │
│ │
│ TOP SHELL │
│ ════════════════════ │
│ │ │
│ ┌──────┴──────┐ │
│ │ │ ← Gasket groove │
│ │ ○○○○○○○○○ │ ← O-ring or foam gasket │
│ │ │ │
│ └──────┬──────┘ │
│ │ │
│ ════════════════════ │
│ BOTTOM SHELL │
│ │
│ Groove dimensions for 2mm cord diameter O-ring: │
│ - Width: 2.5mm │
│ - Depth: 1.5mm │
│ - 25% compression when assembled │
│ │
│ Material: Silicone (temperature resistant) │
│ EPDM (chemical resistant) │
│ Neoprene (general purpose) │
│ │
└─────────────────────────────────────────────────────────────────┘
Surface Finish Options
| Finish | Process | Appearance | Cost |
|---|---|---|---|
| As-machined | None | Tool marks visible | Lowest |
| Bead blasted | Glass bead media | Matte, uniform | Low |
| Brushed | Abrasive belt | Directional lines | Medium |
| Anodized | Electrochemical | Color options, durable | Medium |
| Hard anodized | Type III anodizing | Very hard, dark gray | High |
| Cerakote | Ceramic coating | Custom colors, tactical | High |
Recommendation: Bead blast + Type II anodize (black or natural)
Security Screws
┌─────────────────────────────────────────────────────────────────┐
│ SECURITY SCREW OPTIONS │
├─────────────────────────────────────────────────────────────────┤
│ │
│ TAMPER-RESISTANT: │
│ │
│ Torx Pin Tri-Wing Snake Eye Spanner │
│ ╳ ✱ ⊙ ▬ │
│ (T10 pin) (Nintendo) (Custom) (Slot) │
│ │
│ SERIALIZED (Tier 2+): │
│ │
│ Custom screws with laser-engraved serial numbers │
│ Serial recorded in device OTP memory │
│ Visual inspection detects replacement │
│ │
│ RECOMMENDATION: │
│ Tier 2: Torx Pin (T10) + serialized heads │
│ Tier 3: Custom profile + serialized + epoxy │
│ │
└─────────────────────────────────────────────────────────────────┘
Manufacturing Sources
| Supplier | Region | MOQ | Lead Time | Notes |
|---|---|---|---|---|
| PCBWay CNC | China | 1 | 7-14 days | Good for prototypes |
| Xometry | Global | 1 | 3-10 days | Instant quotes |
| Protolabs | US/EU | 1 | 1-7 days | Fastest turnaround |
| Local shops | Local | 1 | Varies | Best for iteration |
| Fictiv | US | 1 | 5-10 days | Good quality |
Cost Estimate (Tier 2 enclosure):
- Prototype (qty 1): €80-150
- Small batch (qty 10): €40-80 each
- Production (qty 100): €20-40 each
Tier 3: High-Security Enclosure
Potted Assembly
┌─────────────────────────────────────────────────────────────────┐
│ POTTED ENCLOSURE │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Cross-section: │
│ │
│ ┌─────────────────────────────────────────────────────┐ │
│ │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ │
│ │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ │
│ │▓▓ ┌───────────────────────────────────────┐ ▓▓│ │
│ │▓▓ │ PCB │ ▓▓│ │
│ │▓▓ │ ┌─────┐ ┌─────┐ ┌─────┐ ┌─────┐ │ ▓▓│ │
│ │▓▓ │ │ MCU │ │ SE1 │ │ SE2 │ │ SE3 │ │ ▓▓│ │
│ │▓▓ │ └─────┘ └─────┘ └─────┘ └─────┘ │ ▓▓│ │
│ │▓▓ └───────────────────────────────────────┘ ▓▓│ │
│ │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ │
│ │▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ │
│ └─────────────────────────────────────────────────────┘ │
│ │
│ ▓▓▓ = Aluminum-filled epoxy potting compound │
│ │
│ Properties: │
│ - Drilling creates conductive aluminum debris │
│ - Debris causes short circuits (tamper detection) │
│ - Thermal conductivity assists heat dissipation │
│ - Chemical resistance to common solvents │
│ │
└─── ──────────────────────────────────────────────────────────────┘
Potting Compounds
| Product | Type | Thermal Conductivity | Notes |
|---|---|---|---|
| MG Chemicals 832TC | Epoxy | 1.0 W/m·K | Good balance |
| Loctite Stycast 2651 | Epoxy | 0.8 W/m·K | Industry standard |
| Custom (Al-filled) | Epoxy | 1.5+ W/m·K | Maximum security |
| Silicone (RTV) | Silicone | 0.2 W/m·K | Reworkable (avoid) |
Potting Process:
- Clean and dry PCB assembly
- Apply conformal coat to sensitive areas
- Place in enclosure mold
- Mix potting compound (observe pot life)
- Pour slowly to avoid air bubbles
- Vacuum degas if available
- Cure per manufacturer specs (typically 24h @ 25°C)
Active Tamper Mesh Wrap
┌─────────────────────────────────────────────────────────────────┐
│ FLEX PCB MESH WRAP │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Flexible PCB wraps entire enclosure: │
│ │
│ ┌──────────────────────────────────────────────────────┐ │
│ │ ╔════════════════════════════════════════════════╗ │ │
│ │ ║░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░║ │ │
│ │ ║░░ ┌──────────────────────────────────────┐ ░░║ │ │
│ │ ║░░ │ │ ░░║ │ │
│ │ ║░░ │ ALUMINUM ENCLOSURE │ ░░║ │ │
│ │ ║░░ │ │ ░░║ │ │
│ │ ║░░ │ (with potted PCB) │ ░░║ │ │
│ │ ║░░ │ │ ░░║ │ │
│ │ ║░░ └──────────────────────────────────────┘ ░░║ │ │
│ │ ║░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░║ │ │
│ │ ╚════════════════════════════════════════════════╝ │ │
│ └──────────────────────────────────────────────────────┘ │
│ │
│ ░░░ = Flex PCB with continuous security mesh │
│ ═══ = Connection to internal tamper supervisor │
│ │
│ Flex PCB specifications: │
│ - Material: Polyimide (Kapton) │
│ - Thickness: 0.1mm │
│ - Copper: 18µm (0.5 oz) │
│ - Mesh trace: 0.1mm width, 0.2mm spacing │
│ - Wraps all 6 sides of enclosure │
│ │
└─────────────────────────────────────────────────────────────────┘
EMI Shielding (Optional)
For maximum security, add Faraday cage:
Construction options:
1. Conductive paint (internal)
- Nickel or copper-based paint
- Apply to internal surfaces
- Connect to ground
2. EMI gasket (at seams)
- Beryllium copper fingers
- Conductive foam
- Spiral wound gasket
3. Metal mesh (external)
- Fine copper or stainless mesh
- Soldered to ground
- Under outer shell
Effectiveness: >60dB attenuation at 1GHz
Tamper Evidence
Visual Indicators
┌─────────────────────────────────────────────────────────────────┐
│ TAMPER-EVIDENT FEATURES │
├─────────────────────────────────────────────────────────────────┤
│ │
│ 1. HOLOGRAPHIC SEALS │
│ ┌────────────────────┐ │
│ │ ✦ SIMPLEGO ✦ │ Serial number visible │
│ │ ══════════ │ Void pattern if removed │
│ │ SN: 00001234 │ Unique per device │
│ └────────────────────┘ │
│ │
│ 2. SERIALIZED SCREWS │
│ Laser-engraved serial on screw heads │
│ Recorded in device memory at manufacture │
│ Visual mismatch = tampering │
│ │
│ 3. ULTRASONIC WELDING (Tier 3) │
│ Plastic housing permanently bonded │
│ Cannot be opened without visible damage │
│ Used in combination with metal shell │
│ │
│ 4. GLITTER NAIL POLISH (DIY) │
│ Random glitter pattern over screw heads │
│ Photograph pattern at setup │
│ Compare before use │
│ │
└─────────────────────────────────────────────────────────────────┘
Cryptographic Verification (Tier 3)
┌─────────────────────────────────────────────────────────────────┐
│ CRYPTOGRAPHIC ENCLOSURE VERIFICATION │
├────────────────────────────────────────────────────── ───────────┤
│ │
│ At manufacture: │
│ │
│ 1. Record in SE: │
│ - Screw serial numbers │
│ - Hologram serials │
│ - Enclosure serial │
│ - Hash of photo (optional) │
│ │
│ 2. Sign with device identity key │
│ │
│ At verification: │
│ │
│ 1. Device displays expected serials │
│ 2. User visually compares │
│ 3. Device confirms data is authentic (signed) │
│ 4. Any mismatch = potential tampering │
│ │
│ Cannot be forged without: │
│ - Access to identity private key (in SE) │
│ - Matching physical serials │
│ │
└─────────────────────────────────────────────────────────────────┘
Ergonomics and Usability
Handheld Form Factor
┌─────────────────────────────────────────────────────────────────┐
│ ERGONOMIC GUIDELINES │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Dimensions (T-Deck style): │
│ Width: 110-130mm (comfortable grip) │
│ Height: 70-85mm │
│ Depth: 15-25mm │
│ │
│ Weight targets: │
│ Tier 1: <150g │
│ Tier 2: <250g │
│ Tier 3: <400g │
│ │
│ Features: │
│ - Rounded edges (R3mm minimum) │
│ - Textured grip areas │
│ - Lanyard attachment point │
│ - One-handed operation possible │
│ │
│ Hand grip zones: │
│ │
│ ┌─────────────────────────────────────┐ │
│ │ DISPLAY AREA │ │
│ │ │ │
│ ├─────────────────────────────────────┤ │
│ │░░░░│ KEYBOARD AREA │░░░░│ │
│ │░░░░│ │░░░░│ ░░ = Grip zones │
│ │░░░░│ │░░░░│ │
│ └─────────────────────────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────────┘
Pager Form Factor
┌────────────────── ───────────────────────────────────────────────┐
│ PAGER FORM FACTOR │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Dimensions: │
│ Width: 60-80mm │
│ Height: 90-110mm │
│ Depth: 12-18mm │
│ │
│ Features: │
│ - Belt clip attachment │
│ - Lanyard hole │
│ - Minimal controls (encoder + 2-3 buttons) │
│ - E-Ink display (always visible) │
│ │
│ Front view: Side view: │
│ ┌───────────┐ ┌────┐ │
│ │ │ │ │ │
│ │ E-INK │ │ │ ← Belt clip │
│ │ DISPLAY │ │ │ │
│ │ │ │ │ │
│ ├───────────┤ │ │ │
│ │ ○ ◎ ○ │ └────┘ │
│ └───────────┘ │
│ Buttons Encoder │
│ │
└─────────────────────────────────────────────────────────────────┘
Thermal Management
Heat Dissipation
┌─────────────────────────────────────────────────────────────────┐
│ THERMAL DESIGN │
├─────────────────────────────────────────────────────────────────┤
│ │
│ Heat sources: │
│ - MCU: 0.3-0.8W (peak during crypto) │
│ - WiFi: 0.2-0.5W (during TX) │
│ - LoRa: 0.5-1.0W (during TX, if 1W PA) │
│ - Display: 0.1-0.3W (backlight) │
│ - Total peak: ~2-3W │
│ │
│ Thermal path: │
│ │
│ ┌─────────┐ │
│ │ MCU │ │
│ └────┬────┘ │
│ │ Thermal pad │
│ ▼ │
│ ┌─────────┐ │
│ │ PCB │ (2oz copper, thermal vias) │
│ └────┬────┘ │
│ │ Thermal interface material │
│ ▼ │
│ ┌─────────┐ │
│ │ ENCLOSURE│ (aluminum = heatsink) │
│ └────┬────┘ │
│ │ Convection │
│ ▼ │
│ AIR │
│ │
│ Design rules: │
│ - Place hot components near enclosure contact points │
│ - Use thermal vias under QFN/BGA (3×3 array minimum) │
│ - 0.5mm thermal pad between PCB and enclosure │
│ - Aluminum enclosure acts as heatsink (Tier 2+) │
│ │
└─────────────────────────────────────────────────────────────────┘
Connector and Port Placement
Standard Layout
┌─────────────────────────────────────────────────────────────────┐
│ PORT PLACEMENT │
├─────────────────────────────────────────────────────────────────┤
│ │
│ TOP VIEW: │
│ ┌─────────────────────────────────────┐ │
│ │ DISPLAY │ │
│ │ │ │
│ └─────────────────────────────────────┘ │
│ │
│ RIGHT SIDE: BOTTOM: LEFT SIDE: │
│ ┌───┐ ┌─────────┐ ┌───┐ │
│ │ │ │ │ │ │ │
│ │ ○ │ ← Power │ ▭ USB-C │ │ ○ │ ← Headphone │
│ │ │ button │ │ │ │ (optional) │
│ │ │ │ ▯ SD │ │ │ │
│ │ ○ │ ← Volume │ Card │ │ │ │
│ │ │ (optional) │ │ │ │ │
│ └───┘ └─────────┘ └───┘ │
│ │
│ USB-C on bottom: │
│ - Allows charging while standing │
│ - Cable doesn't interfere with grip │
│ - Access while in case/holster │
│ │
│ Avoid: │
│ - Ports on top (blocks display) │
│ - Ports on back (blocks grip) │
│ │
└─────────────────────────────────────────────────────────────────┘
Waterproofing Ports (IP67)
USB-C waterproofing options:
1. Port plug (included)
- Silicone plug attached by tether
- User removes to charge
- IP67 when inserted
2. Sealed magnetic connector
- Magnetic pogo pins
- Gasket around connector
- Always sealed
3. Wireless charging only
- No exposed ports
- Qi charging coil internal
- Maximum sealing
Bill of Materials (Enclosure)
Tier 1 BOM
| Item | Description | Source | Cost |
|---|---|---|---|
| Top shell | PETG 3D print | Self/service | €3-5 |
| Bottom shell | PETG 3D print | Self/service | €3-5 |
| Screws | M2×8 Phillips (×4) | Hardware store | €1 |
| Inserts | M2 brass heat-set (×4) | AliExpress | €1 |
| Feet | Silicone bumpers (×4) | Amazon | €2 |
| Total | €10-14 |
Tier 2 BOM
| Item | Description | Source | Cost |
|---|---|---|---|
| Top shell | 6061-T6 CNC | Xometry/PCBWay | €40-60 |
| Bottom shell | 6061-T6 CNC | Xometry/PCBWay | €40-60 |
| Anodizing | Black Type II | Included | - |
| Gasket | Silicone O-ring | McMaster-Carr | €5 |
| Screws | Torx Pin M2.5×8 (×6) | Security Fasteners | €8 |
| Inserts | M2.5 brass threaded (×6) | DigiKey | €3 |
| Tamper seals | Holographic (×2) | Custom print | €5 |
| Total | €101-141 |
Tier 3 BOM
| Item | Description | Source | Cost |
|---|---|---|---|
| Outer shell | 7075-T6 CNC | Protolabs | €80-120 |
| Inner frame | 6061-T6 CNC | Protolabs | €40-60 |
| Hard anodize | Type III | Included | - |
| Flex mesh PCB | Custom 6-side wrap | PCBWay flex | €30-50 |
| Potting compound | Al-filled epoxy, 200g | Specialized | €20 |
| Gaskets | EPDM, multi-point | Custom | €15 |
| Security screws | Custom + serialized | Specialty | €20 |
| Tamper seals | Crypto-verified | Custom | €10 |
| Total | €215-295 |
File Deliverables
Complete Enclosure Package
enclosures/
├── tier1_diy/
│ ├── cad/
│ │ ├── simplego_diy.step # Universal CAD
│ │ ├── simplego_diy.f3d # Fusion 360
│ │ └── simplego_diy.FCStd # FreeCAD
│ ├── stl/
│ │ ├── top_shell.stl
│ │ ├── bottom_shell.stl
│ │ └── button_caps.stl
│ ├── drawings/
│ │ └── assembly.pdf
│ └── README.md
│
├── tier2_secure/
│ ├── cad/
│ │ ├── simplego_secure.step
│ │ └── simplego_secure.f3d
│ ├── drawings/
│ │ ├── top_shell_drawing.pdf
│ │ ├── bottom_shell_drawing.pdf
│ │ └── gasket_drawing.pdf
│ ├── manufacturing/
│ │ └── cnc_notes.md
│ └── README.md
│
├── tier3_vault/
│ ├── cad/
│ │ └── ... (NDA may apply)
│ ├── flex_pcb/
│ │ └── tamper_mesh_wrap.kicad_pcb
│ └── README.md
│
└── common/
├── hardware/
│ ├── screws.md
│ ├── inserts.md
│ └── gaskets.md
└── suppliers.md
Design Checklist
Before Manufacturing
- PCB dimensions match enclosure cavity
- Display cutout aligned with PCB
- Button/switch cutouts correct size and position
- USB-C port accessible
- Antenna keepout area clear
- Mounting holes align with PCB
- Gasket groove dimensions correct
- Thermal pad contact points defined
- Assembly sequence documented
- Tolerance analysis complete
For Security (Tier 2+)
- Tamper seal locations defined
- Screw serials can be recorded
- Light sensor window designed
- Mesh flex PCB fits
- Potting volume calculated
- No external probe points
- EMI considerations addressed