4.6 System Test, Calibration, and Pack-Out Specification

A Printed Circuit Board Assembly (PCBA) that has passed In-Circuit Testing (ICT) is not a finished product. Mechanical system integration introduces unique, system-level failure modes: pinched custom cables, acoustically blocked microphones, thermal shutdowns due to poor TIM application, and optical sensor misalignment. System Test is the absolute final filter before the customer opens the box. Failing to test the device in its fully assembled, sealed state guarantees that the customer becomes the de facto Quality Control (QC) inspector.

Functional Testing (FCT) Strategy: Objective over Subjective

Human operator judgment must be eliminated completely. “Does the speaker sound good?” is not an engineering test specification. “Does a 1 kHz sine wave measure > 85 dB SPL on the reference mic?” is a valid test specification.

1. Power and Boot Sequence

Current Profiling: The exact current draw during initial boot, active load, and deep sleep state must be measured.
- Logic: When Sleep Current > 50 µA (Target: 10 µA), this indicates a hardware current leak or a firmware bug failing to enter the deep sleep state and fails the test.
Buttons / User Interface (UI): Asking operators to simply “press all the buttons” is prohibited. A test fixture with pneumatic physical actuators must be used, or the operator must be required to follow a randomized on-screen prompt sequence to formally verify the hardware interrupt mapping.

2. Audio and Optical Sensors

Audio: The unit must be placed inside a sound-isolating shielded box. A logarithmic frequency sweep must be played. The acoustic response must be measured using a calibrated reference microphone. The software must automatically compare the result against a predefined “Golden Curve” tolerance mask.
Sensors (Ambient Light / Proximity - ALS): A standardized grey-card target placed at a fixed mechanical distance must be used. The sensor must read within a specific lux/reflectance range. This definitively proves the optical sensor window is not blocked by a misaligned internal foam gasket.

Calibration vs. Verification

The engineering difference between establishing a baseline and checking a limit must be strictly understood.

Calibration: The software reads a known reference value (e.g., placing the unit in a precise 25˚C thermal chamber) and writes an offset correction value into the device’s EEPROM.
Verification: The device reads the current value. If it falls outside the acceptable engineering tolerance (e.g., ± 1˚C), the unit fails.
The Rule: The process must always Calibrate first, then Verify. Performing a calibration and shipping the unit without a subsequent post-calibration verification step is strictly prohibited.

Safety Compliance (High Voltage / AC Mains)

If the device plugs into a wall outlet (AC Mains), electrical safety testing is not an optional quality check; it is a strict legal requirement.

Hi-Pot (Dielectric Withstand Test): A high voltage (e.g., 1500 V AC) must be applied between the live/neutral AC pins and the metallic chassis/ground. The measured leakage current must remain safely below a defined limit (e.g., < 5 mA).
Ground Bond (Earth Continuity): It must be verified that the earth ground pin on the AC plug has a guaranteed low-resistance path (< 0.1 Ohms) to every exposed metallic surface on the product enclosure.
Warning: Repeated AC Hi-Pot testing can degrade internal insulation. “DC Hi-Pot” must be used if repetitive testing is required for debugging, or limit the AC test duration as defined by the safety standard.

Burn-In and Ongoing Reliability Testing (ORT)

Burn-in is designed specifically to catch “Infant Mortality” (early-life component failures) before the unit leaves the factory.

When working with a New Product or New Process: A 100% Burn-In requirement must be implemented for the first production batches (e.g., 4 hours active running at 40˚C, while continuously power cycling).
When a Mature Product: A transition to ORT (Ongoing Reliability Testing) is required. A random sample (e.g., 5 units) must be pulled from every production lot and run at elevated stress for 24 hours. If any unit fails the ORT, the shipment lot must be quarantined and investigated.

Pack-Out: The Final Assembly Step

Packaging the product into the gift box is a formal BOM-driven assembly process, not a janitorial cleanup task. Missing cables or missing manuals cause customer returns just as quickly as a broken motherboard.

1. The Packaging BOM

Treat the cardboard box, the protective foam inserts, and the polybags as engineered mechanical parts.

Sequence: The exact packing order must be defined in the Work Instructions. (e.g., 1. Insert Foam Bottom. 2. Place Device. 3. Insert Accessory Box. 4. Lay down the Quick Start Guide).
Scanning: The operator must scan the physical Device Serial Number and the printed barcode on the Gift Box to digitally link them in the database.
Weight Check: The final, sealed box must be placed on a highly accurate digital scale.
- Logic: When the total box weight deviates by more than the weight of 1 power cable, the box should be rejected to catch missing accessories.

2. Out-of-Box Audit (OBA) Simulation

Right before the gift box is sealed, perform a “Final Cosmetic Inspection” under standardized, bright inspection lighting (e.g., 800-1000 Lux).

Criteria: The device must be inspected exactly as the customer will see it for the first time. The unit must be checked for operator fingerprints, smudges, handling scratches, and inconsistent panel gaps. Operators must be required to wipe the unit down with a microfiber cloth if necessary.

The Device History Record (DHR)

Every single serialized product shipped must have a permanent digital “birth certificate” stored in the factory’s cloud/database. Authorizing a shipment without verifying this record exists is strictly prohibited.

Mandatory DHR Fields:

System Serial Number.
PCBA Serial Number(s) (Parent-Child Linkage).
Radio MAC Addresses / IMEI.
Firmware Version (The exact hash/version flashed at the time of shipment).
Calibration Offsets (Audio/Thermal/RF baseline values).
Test Results: The Pass/Fail status for every individual test station (Safety, FCT, Optical).
Timestamp and Operator ID for the final Pack-Out step.

Final Checkout: System test, calibration, and pack-out specification

Control Point	Critical Requirement
Test Automation	Subjective human judgment must be eliminated. Use reference sensors/cameras for Audio & Video.
Safety Testing	Hi-Pot and Ground Bond are mandatory for AC Mains devices. All test logs must be saved.
Calibration	The strict sequence is Calibrate ⭢ then Verify. Never skip the verification pass.
Sleep State	Deep sleep leakage current must be explicitly measured to guarantee field battery life.
Traceability	A definitive DHR (Device History Record) cloud record must link the Serial Number, FW Version, and all Test Data.
Pack-Out	Final box weight check is required to confirm no missing accessories.
Firmware Lock	The test script must automatically verify the flashed FW version matches the BOM requirement.
Cosmetics	The final OBA (Out of Box Audit) inspection station must have defined, bright lighting (800 – 1000 Lux).