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 that ICT cannot catch, such as pinched custom cables, acoustically blocked microphones, thermal shutdowns due to poor thermal interface material (TIM) application, and optical sensor misalignment. System Test is the final and most critical filter before the customer receives the product. If we fail to test the device in its fully assembled, sealed state, we effectively outsource our quality control to the customer, guaranteeing a poor experience.

Functional Testing (FCT) Strategy: Objective over Subjective

Our goal is to eliminate human operator judgment from the pass/fail decision. Asking an operator, “Does the speaker sound good?” is not a valid engineering test. A proper test specification would be: “Does a 1 kHz sine wave measure greater than 85 dB SPL on the reference microphone?“

1. Power and Boot Sequence

Current Profiling: We must measure the exact current draw during key operational states: initial boot, under active load, and in deep sleep.
Pro-Tip: If the sleep current measures above 50 µA (with a target of 10 µA), it indicates a hardware current leak or a firmware bug preventing proper entry into the deep sleep state. This constitutes a test failure.
Buttons / User Interface (UI): We cannot rely on operators to simply “press all the buttons.” Verification requires either a test fixture with pneumatic actuators or a software-driven process where the operator must follow a randomized on-screen prompt sequence. This formally validates 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 is played, and the acoustic response is measured using a calibrated reference microphone. The test software must then automatically compare the resulting curve against a predefined “Golden Curve” tolerance mask.
Sensors (Ambient Light / Proximity - ALS): We use a standardized grey-card target placed at a fixed mechanical distance. The sensor must read within a specific lux or reflectance range. This test definitively proves the optical sensor window is not blocked by a misaligned internal foam gasket or other obstruction.

Calibration vs. Verification

It’s important to understand the engineering difference between establishing a baseline (calibration) and checking a limit (verification).

Calibration: The process where software reads a known reference value—for example, by placing the unit in a precise 25˚C thermal chamber—and writes a calculated offset correction value into the device’s non-volatile memory (EEPROM).
Verification: The process where the device reads a current value. If that reading falls outside the acceptable engineering tolerance (e.g., ±1°C), the unit fails.
The Rule: The process must always Calibrate first, then Verify. Shipping a unit after calibration without performing the subsequent verification step is not permitted, as it leaves the calibration result unconfirmed.

Safety Compliance (High Voltage / AC Mains)

For any device that plugs into a wall outlet (AC Mains), electrical safety testing is not an optional quality check—it is a strict legal and regulatory requirement.

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

Burn-In and Ongoing Reliability Testing (ORT)

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

For a New Product or New Process: Implement a 100% Burn-In requirement for the first production batches. A typical profile might involve 4 hours of active running at 40°C while continuously power cycling the units.
For a Mature Product: Transition to an ORT (Ongoing Reliability Testing) sampling plan. For example, randomly pull 5 units from every production lot and run them under elevated stress for 24 hours. If any unit fails the ORT, the entire shipment lot must be quarantined and a root-cause investigation initiated.

Pack-Out: The Final Assembly Step

Packaging the product into its retail box is a formal, bill-of-materials (BOM) driven assembly process. It is not a simple cleanup task. Missing cables or manuals cause customer returns just as reliably as a faulty motherboard.

1. The Packaging BOM

We must treat the cardboard box, protective foam inserts, and polybags as engineered mechanical parts with defined specifications.

Sequence: The exact packing order must be defined in the Work Instructions. For example:
1. Insert the bottom foam piece.
2. Place the device.
3. Insert the accessory box.
4. Lay down the Quick Start Guide.
Scanning: The operator must scan both the physical Device Serial Number and the printed barcode on the gift box. This digitally links the two in the manufacturing database for full traceability.
Weight Check: The final, sealed box must be placed on a highly accurate digital scale.
Pro-Tip: If the total box weight deviates by more than the weight of one power cable, the system should reject the box. This is an effective method to catch missing accessories.

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

Immediately before sealing the gift box, perform a “Final Cosmetic Inspection” under standardized, bright inspection lighting (e.g., 800–1000 Lux).

Criteria: Inspect the device exactly as the customer will see it for the first time. Check for operator fingerprints, smudges, handling scratches, and inconsistent panel gaps. Operators must be required to wipe the unit down with a microfiber cloth if any contaminants are found.

The Device History Record (DHR)

Every single serialized product shipped must have a permanent digital record—its “birth certificate”—stored in the factory’s cloud database. Authorizing a shipment without verifying the existence and completeness of this record is not allowed.

Mandatory DHR Fields:

System Serial Number.
PCBA Serial Number(s) (establishing parent-child linkage).
Radio MAC Addresses / IMEI.
Firmware Version (the exact hash or version flashed at the time of shipment).
Calibration Offsets (Audio, Thermal, and 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.

Recap: System Test, Calibration, and Pack-Out Specification

Parameter	Requirement	Value	Action
Sleep Current	Measure in deep sleep state	≤ 50 µA (target 10 µA)	Fail unit if exceeded
Audio Response	Compare to golden curve in shielded box	Within predefined tolerance mask	Fail unit if out of tolerance
Sensor (ALS) Reading	Measure with grey-card target at fixed distance	Within specified lux/reflectance range	Fail unit if out of range
Calibration & Verification	Calibrate using reference, then verify reading	Verification tolerance (e.g., ±1°C)	Calibrate first, then verify; fail if verification fails
Hi-Pot Test	Apply high voltage between AC pins and chassis	Leakage current < 5 mA at 1500 V AC	Fail unit if limit exceeded; limit AC test duration per standard
Ground Bond Test	Measure resistance from AC earth pin to chassis	< 0.1 Ω	Fail unit if exceeded
Burn-In / ORT	Run units under stress (active, 40°C, power cycling)	New product: 100%, 4 hours. Mature: sample 5 units/lot, 24 hours	Quarantine entire lot on any ORT failure
Final Box Weight	Weigh sealed retail box	Deviation ≤ weight of one power cable	Reject box if deviation exceeded
Device History Record (DHR)	Record must exist and be complete for each serialized unit	Contains all mandatory fields (SN, PCBA SN, MAC, FW, Calibration, Test Results, Timestamp)	Do not authorize shipment without complete DHR