3.5: HWE.3 Hardware Implementation

Process Purpose: Execute the detailed design (HWE.2) - source components, fabricate PCBs, assemble boards, perform basic functionality checks. Deliver physical hardware ready for verification testing.

Implementation Activities

1. Component Procurement

Process:

• Issue purchase orders (POs) to qualified suppliers
• Verify component authenticity (counterfeit detection)
• Store components in controlled conditions
• Track traceability (batch codes, lot numbers)

Component Sourcing Challenges:

Microcontroller (STM32H755ZI):
├─ Lead time: 16 weeks (typical for safety-critical)
├─ Minimum order: 500 units
├─ Supplier: STMicroelectronics official distributor
└─ Verification: Datasheet, certificate of conformance

Sensor (RTD Pt100):
├─ Lead time: 8 weeks
├─ Source: Multiple suppliers (reduce risk)
└─ Verification: Calibration certificate, accuracy tolerance

Counterfeit Risk Mitigation:
├─ Purchase from authorized distributors only
├─ Request certificates of conformance
├─ Conduct incoming inspection (visual, continuity test)
└─ Implement traceability (lot tracking in assembly)

2. PCB Fabrication

Vendor Selection:

• IPC Class 2 (general electronics) or Class 3 (safety-critical)
• Controlled impedance (for signal integrity)
• Trace width/spacing compliance
• Flying probe testing (open/short circuits)

Fabrication Spec:

Layer count: 4 layers
Material: FR-4, Tg ≥170°C
Copper weight: 1 oz (top/bottom), 2 oz (inner power/ground)
Via size: 0.010" drill, 0.019" pad
Trace width: ≥4 mil (signal), ≥8 mil (power)
Solder mask: LPI (liquid photoimageable)
Silkscreen: Component labels, orientation marks

Quality Assurance:

• [PASS] Automated Optical Inspection (AOI)
• [PASS] Flying probe test (connectivity)
• [PASS] X-ray inspection (via quality)
• [PASS] Certificate of conformance provided

3. Component Assembly

Method: Pick-and-place with reflow soldering (surface-mount)

Process Steps:

Step 1: PCB Preparation
  ├─ Solder paste application (stencil printing)
  └─ Inspection: Paste coverage ≥90%

Step 2: Component Placement
  ├─ Automated pick-and-place machine
  ├─ Vision-guided placement (±0.1mm accuracy)
  └─ Inspection: Component orientation, placement accuracy

Step 3: Reflow Soldering
  ├─ Thermal profile (ramp-up, peak, cool-down)
  ├─ Peak temperature: 245-260°C
  ├─ Time above liquidus (217°C): 60-90 seconds
  └─ Cool-down rate: <6°C/second (avoid thermal stress)

Step 4: Quality Inspection
  ├─ Automated Optical Inspection (AOI)
  ├─ X-ray inspection (solder joint quality)
  └─ Manual rework (any defects)

Step 5: Functional Test (Basic)
  ├─ Power supply (voltage, current)
  ├─ Oscillator (frequency accuracy)
  ├─ GPIO (input/output response)
  └─ Pass/fail rate target: >99%

4. Traceability & Documentation

Traceability Implementation:

Component Traceability Chain:
├─ Supplier (STMicroelectronics official distributor)
├─ PO number (PO-2025-1234)
├─ PCB lot (PCB-Lot-2025-056)
├─ Assembly date (2025-12-15)
├─ Assembly batch (Batch-A-2025-12)
├─ Serial number (HW-001-2025)
└─ Test date (2025-12-20)

Documentation:
├─ Bill of Materials (BOM) with part numbers
├─ Assembly work instructions
├─ Solder profiling (temperature log)
├─ Test results (pass/fail per board)
└─ Assembly photos (quality evidence)

Manufacturing Defect Management

Defect Categories

Yield Analysis

Target: 98% first-pass yield

Actual Results (100 boards):
├─ Pass: 97 boards (97% yield)
├─ Failures: 3 boards
│  ├─ Cold solder joints (2 boards) → Rework
│  └─ Missing capacitor (1 board) → Scrap
└─ After rework: 99 boards (99% yield)

Actions:
├─ Reflow oven calibration (improve temperature uniformity)
├─ Pick-and-place verification (detect missing component)
└─ Target next batch: ≥99%

Documentation Deliverables

HWE.3 Outputs:

1. Manufacturing Records (POs, receipts, traceability)
2. Assembly Work Instructions (step-by-step procedures)
3. Test Records (pass/fail results per board, defect logs)
4. Configuration Baseline (BOM revision, solder profile settings)
5. Traceability Matrix (component lot → board serial number)

Summary

HWE.3 Outcomes:

• [PASS] PCBs fabricated per design specification
• [PASS] Components sourced and verified (counterfeit-free)
• [PASS] Boards assembled with >99% yield
• [PASS] Functional tests passed (basic power-up test)
• [PASS] Traceability established (lot tracking)
• [PASS] Ready for detailed verification testing (HWE.4)

Next: HWE.4 (Verification testing)