Advantages and Precautions of Manual Soldering for PCBA

Manual Soldering for PCBA

PCB (Printed Circuit Board) is an indispensable component in electronic products. Soldering is a crucial step in connecting electronic components to PCBs. There are various soldering techniques, such as wave soldering, reflow soldering, and infrared soldering. Today, we will discuss manual soldering techniques.

What is manual soldering? Manual soldering is the process of manually connecting electronic components to printed circuit boards (PCBs) using a soldering iron or soldering station. The soldering iron is used to melt the solder, which is a low-melting-point metal alloy, forming a bond between the electronic component and the PCB. This process is crucial for establishing electrical connections between components and PCBs, ensuring the normal functionality of electronic devices.


Advantages of Manual Soldering for PCBA:

  1. Addressing Complexities: Manual soldering effectively addresses issues that automated machinery may struggle with, especially concerning intricate PCB layouts or small, irregularly shaped components.
  2. Precision: Skilled technicians perform manual soldering, ensuring high precision and quality of solder joints.
  3. Human Adjustment: Manual soldering allows for human intervention to rectify soldering errors, thereby enhancing the overall quality of PCB assemblies.
  4. Versatility: Manual soldering is suitable for a wide range of applications, particularly for handling small batches, high-reliability, and highly flexible products, compared to automated production lines.
  5. Cost-effectiveness: Manual soldering tends to be more cost-effective compared to automated production lines.

In summary, manual soldering holds significant advantages in the PCBA processing field. While automated machinery continues to evolve and replace manual soldering in many areas, manual soldering will still persist in certain special circumstances.


Selection of Soldering Materials and Flux:

(1) Soldering Materials: According to the composition, soldering materials include tin-lead solder, silver solder, copper solder, etc. Tin-lead solder is predominantly used in the assembly of general electronic products due to its advantages over pure lead and tin:

  • Low Melting Point: Various tin-lead alloy compositions have melting points lower than those of pure lead and tin, facilitating the soldering process.
  • High Mechanical Strength: Tin-lead alloys exhibit superior mechanical strength compared to pure tin and lead.
  • Low Surface Tension: Reduced viscosity enhances liquid flowability, facilitating the formation of reliable joints during soldering.
  • Good Oxidation Resistance: The antioxidation properties of lead are maintained in the alloy, minimizing oxidation during solder melting.

(2) Flux: Fluxes are categorized into rosin flux (rosin-based) and soldering flux (resin-based).

Soldering flux serves three main purposes:

  1. Oxide Removal: Flux helps remove oxide films from surfaces.
  2. Oxidation Prevention: It prevents further oxidation during soldering.
  3. Surface Tension Reduction: Flux reduces surface tension, enhancing the flowability of solder and aiding in wetting the solder to the workpiece.

Manual Soldering PCBA

Precautions for Manual Soldering in PCBA:

  1. Use an anti-static wristband to prevent IC damage from human static electricity.
  2. Wear gloves or finger cots to avoid direct contact with bare hands.
  3. Control soldering temperature, angle, sequence, and duration.
  4. Hold the edges of the PCB when handling to avoid touching components.
  5. Opt for low-temperature soldering to prevent tip oxidation.
  6. Avoid applying excessive pressure to prevent tip damage.
  7. Avoid tapping or shaking the soldering iron during soldering.
  8. Use a damp sponge to clean the soldering iron tip from oxides and solder residues.
  9. Properly apply solder and flux to avoid defects and failures.
  10. Keep the soldering iron tip tinned regularly to reduce oxidation.
  11. Watch out for flux splatter and solder ball issues.
  12. Prevent overheating insulation layers and surrounding components.
  13. Perform self-checks, inspecting solder joint appearance, response, AOI, and fault recurrence regularly.


Quality Inspection for Manual Soldering in PCBA:

  1. Visual Inspection of PCBA Samples: Quality Control (QC) visually inspects the solder joint appearance of circuit boards, utilizing microscopes for detailed examination when necessary.
  2. Testing Circuit Board Responses: Using a multimeter, circuit board resistances are tested at room temperature, examining surrounding solder points for any signs of faults.
  3. AOI Inspection: Conducting X-ray inspections on circuit boards, particularly focusing on detecting abnormal connections near resistors, any anomalies in connectors on the board, unusual internal copper wire formations, and potential resistor irregularities.
  4. Fault Reproduction: To validate the failure mode of the circuit board and identify the cause of failure, both resistive and non-resistive circuit boards undergo constant temperature and humidity tests.

In summary, manual soldering in PCBA is a traditional soldering technique that involves manually connecting electronic components to PCBs using soldering irons and solder. It offers advantages such as high flexibility, relatively low technical requirements, and lower costs, making it suitable for small-scale production and prototype development. Despite advancements in technology, manual soldering remains an irreplaceable process, playing a crucial role in the PCBA manufacturing process.


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