PCBA processing

Inspection standard for PCBA processing

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Printed Circuit Board Assembly (PCBA) inspection is a crucial process in electronic device manufacturing. It involves examining the quality of PCBs and their components to ensure they meet necessary specifications and standards. PCBA inspection is a vital aspect of quality control as it helps prevent defects and failures in the final product. In this article, we will discuss in detail the inspection and acceptance criteria for PCBA boards.

PCBA Inspection Process

The PCBA inspection process typically involves a combination of automated and manual checks. The first step of the process is visual inspection, which includes examining the PCB for any physical defects such as cracks, scratches, or damage to solder mask layers. This is usually manually performed by trained inspectors using magnifying glasses or microscopes.

The next step is Automated Optical Inspection (AOI), which uses cameras and software to detect defects such as missing components, misaligned components, and soldering defects. AOI is a fast and accurate inspection method capable of detecting defects that may be difficult for humans to identify.

Following AOI, the circuit board may undergo X-ray inspection, which is used to detect defects in hidden areas such as solder joints beneath surface-mounted components. X-ray inspection is particularly useful for detecting defects like voids in solder joints, which may be challenging to detect using other methods.

PCBA Component Design and Inspection Specifications

Inspection Preparation: Inspectors must wear anti-static gloves and wristwatches and prepare tools such as calipers, electrical performance parameter instruments, etc.

  1. Technical Requirements

1.1 PCBA component boards must use materials with a flame retardancy rating of 94-V0 or above, with corresponding UL yellow cards.

1.2 The appearance of PCBA component boards should be free of rough burrs, poor cutting, and layer cracking.

1.3 The dimensions, apertures, and margins of PCBA component boards must comply with the engineering drawings’ requirements, with a tolerance of ±0.1mm unless otherwise specified. The thickness of the boards should be 1.6±0.1mm unless otherwise specified.

1.4 PCBA components must print the production (design) date, UL symbol, certificate number, 94V-0 character, factory logo, and product model. If the PCBA component consists of multiple PCB boards, the rest of the PCB boards should also print the above content.

1.5 The printed symbols and font sizes should be clear and distinguishable.

1.6 If PCBA components use resistor-capacitor voltage reduction circuits, they must use half-wave rectification circuits to improve circuit safety and stability.

1.7 If PCBA components use switch-mode power supply circuits, the standby power consumption must be less than 0.5W.

1.8 European products using PCBA must have standby power consumption less than 1W. For the US version of PCBA, if customers have special requirements, standby power consumption should be executed according to technical requirements.

1.9 Except for power indicator lights using φ5 amber high-brightness scattering, the rest should use full green or full red φ3 high-brightness scattering.

1.10 PCBA components specify the live wire (ACL), neutral wire (ACN), relay common terminal wire (ACL1), high-grade or continuous wire (HI), and low-grade wire (LO).

1.11 The solder fuse and CBB capacitor (resistor-capacitor circuit) of PCBA components must be on the live wire (ACL).

1.12 ACL1 must be connected to the live wire, HI or LO must be connected to one end of the heating body each, and the common terminal of the heating body must be connected to the neutral wire.

1.13 The solder joints of PCBA components must not have virtual soldering, continuous soldering, or desoldering. The solder joints should be clean, uniform, and free of bubbles, pinholes, etc.

  1. Component Selection

2.1 PCBA component elements should be prioritized from reputable brand manufacturers, followed by manufacturers that meet international or industry standards; manufacturers with proprietary standards should not be used.

2.2 Integrated circuit (IC) components should be industrial-grade ICs.

2.3 Connector plugs and terminals must have UL certification and provide certificates.

2.4 Resistor components should use metal film resistors with clear color bands, and manufacturers should meet industry standards.

2.5 Electrolytic capacitor components should use explosion-proof capacitors with a working temperature of -40 to 105°C, and manufacturers should meet industry standards.

2.6 Crystal oscillator components should use crystal elements; RC or chip-embedded options are not recommended. Manufacturers should meet international standards.

2.7 Diodes or transistors should be selected from reputable domestic brands that meet industry standards.

2.8 Tilt switches should use infrared photoelectric types and avoid mechanical types.

2.9 Specified component surfaces must be printed with clear and visible UL/VDE/CQC symbols, trademarks, parameters, etc.

2.10 Relevant wires must have UL/VDE symbols, wire specifications, certification numbers, manufacturer names, etc., clearly visible.

  1. Testing and Inspection

3.1 PCBA components are mounted on the corresponding test fixtures, and voltage frequency parameters are adjusted accordingly.

3.2 Verify whether the self-check function of the PCBA components meets the requirements of the functional specifications. Check for abnormal sounds in relay outputs and uniform brightness in fully lit LEDs.

3.3 Verify whether the placement of the tilt device and the output function during tilting comply with the functional specifications.

3.4 Check whether the output function and fault indication of the PCBA components meet the functional specifications when the temperature probe is disconnected or shorted.

3.5 Verify whether the output of each button function of the PCBA components meets the requirements of the functional specifications.

3.6 Check whether the temperature indicated by the environmental temperature indication LED or digital display of the PCBA components complies with the functional specifications.

3.7 Verify whether the power status indication LED of the PCBA components meets the functional specifications.

3.8 Check whether the smart control operation mode of the PCBA components complies with the functional specifications.

3.9 Verify whether the continuous operation mode of the PCBA components complies with the functional specifications.

3.10 Check whether the standby power consumption of the PCBA components complies with the functional specifications.

3.11 Adjust the voltage to 80% of the rated voltage, and check for abnormal sounds in relay outputs and uniform brightness in LEDs.

3.12 Adjust the voltage to 1.24 times the rated voltage, and check for abnormal sounds in relay outputs and uniform brightness in LEDs.

PCBA General Appearance Inspection specification

  1. Solder Joint Contact Angle Defect: The wetting angle between the angle solder fillet and the terminal pad graphic endpoint exceeds 90°.

  2. Standing: One end of the component is raised or standing up from the solder pad.

  3. Short Circuit: The solder between two or more solder joints that should not be connected, or the solder of the solder joint is connected to adjacent wires.

  4. Open Solder: The component leads are not soldered to the PCB solder pads.

  5. False Solder: The component leads are seemingly connected to the PCB solder pads but are not actually connected.

  6. Cold Solder: The solder paste at the solder joint is not fully melted or does not form a metal alloy.

  7. Insufficient Solder (Insufficient Fill): The solder area or height of the component terminal and PAD does not meet the requirements.

  8. Excessive Solder (Excessive Fill): The solder area or height of the component terminal and PAD exceeds the requirements.

  9. Solder Joint Blackening: The solder joint is blackened and lacks luster.

  10. Oxidation: Chemical reaction has occurred on the surface of components, circuits, PADs, or solder joints, resulting in colored oxides.

  11. Displacement: The component deviates from the predetermined position in the plane of the solder pad horizontally, vertically, or rotationally (based on the centerline of the component and the centerline of the solder pad).

  12. Polarity Reversal: The orientation or polarity of components with polarity does not match the requirements of documents (BOM, ECN, component position diagram, etc.).

  13. Float Height: There is a gap or difference in height between the component and the PCB.

  14. Wrong Part: The specifications, models, parameters, and forms of the components do not match the requirements of documents (BOM, samples, customer data, etc.).

  15. Solder Tip: The component solder joint is not smooth and has a pulled tip condition.

  16. Multiple Parts: The positions of parts that should not be mounted according to the BOM, ECN, or samples, or there are surplus parts on the PCB.

  17. Missing Parts: The positions on the PCB where parts should be mounted according to the BOM and ECN or samples, but no parts are present.

  18. Misalignment: The position of the component or component pin has shifted to other PADs or pin positions.

  19. Open Circuit: PCB circuit is disconnected.

  20. Side Mounting: Sheet-like components with differences in width and height are mounted sideways.

  21. Reverse Side (Upside Down): Two symmetrical faces of components with differences are swapped (e.g., faces with silk screen markings are inverted vertically), common in chip resistors.

  22. Solder Ball: Small solder points between component pins or outside PADs.

  23. Bubbles: There are bubbles inside solder joints, components, or PCBs.

  24. Soldering (Solder Climb): The solder height of the component solder joint exceeds the required height.

  25. Solder Cracking: The solder joint has a cracked condition.

  26. Hole Plugging: PCB plug-in holes or vias are blocked by solder or other substances.

  27. Damage: Components, board bottom, board surface, copper foil, circuits, vias, etc., have cracks, cuts, or damage.

  28. Unclear Silk Screen: The text or silk screen on the component or PCB is blurry or has broken lines, making it unrecognizable or unclear.

  29. Dirt: The board surface is unclean, with foreign objects or stains, etc.

  30. Scratches: Scratches or exposed copper foil on the PCB or buttons, etc.

  31. Deformation: The component or PCB body or corners are not on the same plane or are bent.

  32. Bubbling (Delamination): PCB or components delaminate from the copper plating and have gaps.

  33. Glue Overflow (Excess Glue): Excessive amount of red glue (or overflow) exceeds the required range.

  34. Insufficient Glue: The amount of red glue is insufficient or does not meet the required range.

  35. Pinhole (Concavity): There are pinholes or concavities on PCBs, PADs, solder joints, etc.

  36. Burr (Peak): The edge or burr of the PCB board exceeds the required range or length.

  37. Gold Finger Impurities: There are dots, tin spots, or solder resist oil abnormalities on the surface of the gold finger plating.

  38. Gold Finger Scratches: There are scratch marks or exposed copper on the surface of the gold finger plating.