1.8 Quality, Compliance, and “Definition of Done”

In professional electronics manufacturing, "it turns on" is not a quality standard; it is merely the minimum requirement for a prototype. True quality is the absence of variation. A board that functions perfectly but violates IPC assembly standards is a "defect" because it carries a latent risk of failure. Quality Assurance (QA) is the discipline of proving, with data, that the product was built exactly according to the documentation and industry standards, ensuring it will survive in the field long after it leaves the factory.

The Standard: IPC-A-610

You cannot inspect for "goodness." You must inspect for compliance against a binary standard. The electronics industry operates on IPC-A-610 (Acceptability of Electronic Assemblies). This standard divides products into three classes based on reliability requirements.

Class 1: General Electronic Products

• Scope: Toys, cheap consumer gadgets.
• Requirement: Function is the primary goal. Cosmetic imperfections are acceptable.

Class 2: Dedicated Service Electronic Products

• Scope: Laptops, microwaves, industrial controllers.
• Requirement: High performance and extended life. Uninterrupted service is desired, but not critical. This is the industry default.

Class 3: High Performance Electronic Products

• Scope: Aerospace, Medical (Life Support), Automotive safety systems.
• Requirement: Performance on demand is critical. Equipment downtime is not tolerated. Solder criteria are strict (e.g., 75% barrel fill vs 50%).

The Engineering Reality

Specifying Class 3 increases cost significantly because it slows down the line and increases inspection overhead.

• If you do not specify a Class in your documentation → Then the factory will build to Class 2.
• If you demand Class 3 for a disposable IoT sensor → Then you are wasting money on inspection criteria that add no value to the user.

The Inspection Strategy: Trust No One

Human inspection is unreliable. Operators get tired, distracted, or blink. A robust quality plan relies on automated layers of defense (The "Swiss Cheese" model) to catch defects at the earliest possible moment.

1. SPI (Solder Paste Inspection)

• Action: A 3D scanner measures the volume of solder paste on the pads before component placement.
• Logic: 70% of all soldering defects stem from poor paste printing.
• If paste volume is low (< 70%) → Then wipe the board and reprint immediately. Do not solder it.

2. AOI (Automated Optical Inspection)

• Action: Cameras compare the soldered board against a "Golden Board" image.
• Detects: Missing parts, polarity errors, skew, tombstoning.
• Limitation: AOI cannot see hidden solder joints (e.g., under chips).

3. AXI (Automated X-Ray Inspection)

• Action: X-rays penetrate component bodies to inspect solder joints underneath.
• Target: BGAs (Ball Grid Arrays), QFNs, and LGAs.
• If a design uses BGAs but you skip X-Ray → Then you are shipping blind, with no way to verify if the chip is actually soldered.

4. ICT (In-Circuit Test) & FCT (Functional Test)

• Action: ICT checks for shorts/opens electrically. FCT powers the device to check logic.
• Logic: AOI proves it looks right; ICT/FCT proves it acts right.

Traceability: The Audit Trail

When a product fails in the field 18 months from now, you must answer the question: "Why?" Traceability is the data link between a specific serial number and its manufacturing history.

Batch Traceability

"This box of 500 units was built on Tuesday using Solder Paste Lot #123 and Capacitor Reel #456."

• Risk: If one capacitor reel is defective, you must recall the entire batch of 500.

Serial Traceability

"Unit #SN-00192 was built at 14:02, placed by Head 3, and passed Test Station 4 with a voltage reading of 3.31V."

• Benefit: Surgical recalls. You can isolate exactly which units contain the bad components.

Pro-Tip: Always print a barcode or QR code on the PCB silkscreen or label. If the board has no unique ID, you have zero traceability once it leaves the SMT line.

The "Definition of Done"

A production run is not finished when the last unit is packed. It is finished when the Certificate of Conformity (CoC) is signed. The CoC is a legal declaration by the manufacturer that the goods meet the specifications. It must include:

1. Part Number and Revision.
2. Quantity and Batch Code.
3. Statement of Compliance to IPC Class.
4. Test Reports (Pass/Fail summary).

Final Checklist

Control	Function	Metric	Critical Rule
Standard	Visual Criteria	IPC-A-610 (Class 2 or 3)	Define Class in the drawing notes.
SPI	Paste Quality	Volume %	Reject boards with < 70% paste volume.
AOI	Component Check	Presence / Polarity	100% inspection for all SMT runs.
X-Ray	Hidden Joints	Void %	Mandatory for BGA/LGA components.
Traceability	Risk Management	Serial Number	Link Test Results to Serial Numbers.
CoC	Sign-off	Compliance	Do not pay the invoice without the CoC.