What is the standard for electronic assembly?

I. Material Standards

1. Consistency and Compliance: All components, structural parts, and auxiliary materials used must be fully consistent with the models, specifications, parameters, brands, and packages specified in the design drawings and BOM lists.
2. Appearance Quality: The materials themselves should be free from obvious physical damage, such as bent or oxidized pins on components, cracks, scratches, or contamination on PCB boards, and burrs, deformations, or color differences on structural parts.
3. Traceability: Critical materials should be traceable, with clear batch information and supplier details to facilitate the tracing and analysis of quality issues.

II. Assembly Process Standards

1. Component Installation: Components should be installed in the specified direction and polarity, without significant misalignment, tilting, or inversion. The component bodies should be free from damage, cracks, burns, or discoloration. The installation height should meet the specified requirements, and components of the same specification should be installed at approximately the same height.
2. Soldering Quality:
   • Manual Soldering: The soldering iron temperature should match the component type. The soldering time should be controlled within 2-3 seconds to prevent the PCB pads from peeling off. The solder joints should be in a “half-moon” shape, free from cold solder joints, solder bridges, and lifted pad copper foils.
   • Wave Soldering: The flux spraying amount (usually 0.8-1.2 ml/cm²), preheating temperature (90℃-110℃), and soldering time (3-5 seconds) should be optimized to ensure full and bridge-free solder joints. For lead-free soldering (e.g., SAC305 alloy), due to its higher melting point (about 217℃), the temperature profile should be adjusted, and the preheating time should be extended to reduce thermal stress while meeting RoHS environmental requirements.
   • Reflow Soldering: The temperature profile should be set according to the solder paste type (e.g., for Sn63/Pb37 solder paste, the preheating temperature is 120-140℃, and the reflow temperature is 210-220℃). After soldering, check for full and bridge-free solder joints (which can be inspected using AOI).
3. Circuit Connection: Circuit connection is mainly achieved through soldering. Ensure that the solder joints are smooth and firm, without cold solder joints or missing solder joints. Clean the pads before soldering to remove impurities such as oxide layers. During soldering, move the soldering iron tip quickly between the pad and the pin to evenly attach the solder to both, forming a good electrical connection.

III. Appearance Standards

1. Overall Appearance: The product housing should be firmly installed without significant looseness or excessively large gaps. The housing surface should be free from scratches, dents, and should have a uniform color without fading or discoloration.
2. Detail Aspects: All interfaces should be neat and tight, without looseness or poor contact hazards. For products with indicator lights, check whether the indicator lights can illuminate normally and whether the colors are correct. Labels and markings should be clear, accurate, and firmly attached.

IV. Functional Performance Standards

1. Function Verification: Verify each function one by one according to the product’s design requirements. For example, for a simple electronic calculator, test whether its addition, subtraction, multiplication, and division operations are accurate. For an electronic product with a display screen, check whether the display screen can display information normally and whether the displayed content is clear and complete.
2. Performance Indicator Testing: Measure parameters such as voltage, current, and power to ensure they are within the specified ranges. For example, for a charger, measure whether its output voltage and current comply with the specifications marked on the product. For electronic products with signal processing functions, also test indicators such as signal strength, frequency, and distortion.

V. Reliability and Safety Standards

1. Reliability Testing: Includes high- and low-temperature testing, humidity cycling testing, vibration testing, shock testing, and aging testing to evaluate the product’s long-term stable operation capability under different environmental conditions.
2. Safety Testing: Focus on the product’s electrical safety performance, such as insulation resistance, dielectric strength, leakage current, and grounding resistance, to ensure that the product will not cause electric shock, fire, or other safety hazards to users under normal use and fault conditions. In addition, electromagnetic compatibility (EMC) testing may also be involved to ensure that the product does not interfere with other devices and is not susceptible to interference from other devices.

VI. Environmental and Safety Specifications

1. Environmental Control: The assembly workshop temperature should be 20-25℃, and the humidity should be 40%-60%. The humidity in the SMT workshop should be ≥45% to prevent solder paste from cracking. The cleanliness of the workshop should reach ISO Class 8 (particle count ≤ a specific number/m³), and air filters should be replaced regularly to prevent dust from causing short circuits.
2. Electrostatic and Safety Protection: The workshop floor should be laid with anti-static flooring, and the workbench surface should be grounded. Operators should pass an electrostatic test (human body electrostatic ≤ 100V) before entering the workshop. The soldering area should be equipped with smoke exhaust equipment (air velocity ≥ 0.5 m/s) to prevent inhalation of soldering fumes. Operators should receive training before operating equipment, and it is strictly prohibited to wear gloves when operating high-speed rotating equipment (such as lead-cutting machines).