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PCB inspection is one of the most crucial steps in the PCB manufacturing process. PCB inspection helps find flaws during the PCB manufacturing process.
Whether you have large-scale manufacturing or low-volume manufacturing, PCB inspection is an important step. One such type is Manual Inspection.
What does Manual Inspection Mean?
As the name suggests, manual Inspection means the examination of the PCB board visually by an expert individual inspector. It was one of the first and only methods of PCB inspection in the early days.
This method is still in practice because of its simplicity and faster approach. It is the very first step in PCB inspection.
It is one of the widely used processes of inspecting PCBs that depends on trained engineers or technicians who can identify the faults without needing special devices.
The quality and reliability of manual PCB inspection depends on the experience and knowledge of technicians. Also, its cost directly depends on labor and escape costs.
Although manual Inspection is a time-consuming method, it is still necessary in the PCB manufacturing industry.
Let’s look into some of the characteristics of the PCB inspection system:
- It is simple to carry out.
- It is fast and can be added at any time during the manufacturing process,
- It provides all the information required to eliminate the faults present in the circuit board.
Drawbacks of Manual Inspection
Although manual Inspection is a more accessible and simpler method, it has some drawbacks in the PCB manufacturing industry. Some of these drawbacks are as follows:
- For complex circuit boards, it isn’t easy to check the board.
- It can’t find the failures and errors outside of the sign, like hidden solder joints and more.
- It is less effective than other inspection methods.
Steps For Manual Inspection
#1 Review the Inspection Criteria
Review the inspection criteria that your customer asks for. The default type is IPC-1 610 for the electronics component assembly system.
Collect the necessary tools for carrying out the Inspection. This includes a magnifying glass, microscope, lighting work area, or any documentation or specifications of PCB components.
#3 Visual Inspection
Visually inspect the PCB surface for any defects like scratches, damages to the board, solder splashes, discoloration, etc. Check for any missing or misaligned components in the circuit board that may affect the working of the board device.
#4 Component Check
Verify all the components are correctly placed and soldered in PCB. Ensure no solder bridges are present in between adjacent pins or traces.
#5 Solder Joints inspection
Check the solder joints using magnification to ensure they are correctly formed and have sufficient fillets. Check for any signs of poor soldering, like solder balls, cold joints, or insufficient solders.
#6 Trace Inspection
Check for trace integrity or the conductive paths on the PCB to ensure there are no breaks or irregularities.
#7 Quality Standards Compliance
Compare the inspected PCB against quality standards and specifications provided by the manufacturer or industry standards. Ensure that the PCB meets all required criteria for functionality and reliability.
Document any defects or irregularities found during the inspection process. Record their location on the PCB and provide detailed descriptions to aid in troubleshooting and correction.
#9 Final Approval
Once the Inspection is complete and necessary corrections have been made, approve the PCB for further assembly or testing.
Why do we need Manual PCB Inspection?
Inspection is a crucial step in PCB manufacturing. If you find defects in the initial process of PCB manufacturing, you can correct them and improve the overall operations of the process. It can also help to reveal the flaws in design that could exist there. Manual Inspection avoids the rework and also speeds up the project. On the other hand, it provides the customer with added protection without increasing costs.
Let’s break down the characteristics of manual Inspection:
- Simplicity: Manual Inspection doesn’t need fancy equipment; human eyes or magnifying glasses are sufficient.
- Flexibility: It’s a quick process that can be incorporated at any production stage.
- Random Sampling: Typically, manual Inspection is applied randomly to batch orders. For detailed Inspection, precise instruments like AOI or X-RAY are used if faults are found.
- Fault Tolerance: While manual Inspection may not catch every fault, it helps eliminate many when combined with other detection methods.
- Expert Guidance: Experienced inspectors understand circuit board designs and can effectively identify potential issues.
- Limitations: Manual Inspection is limited to visible areas and can’t detect hidden solder joints or faults.
- Error Prone: It’s challenging to spot faults in complex circuit boards, and inexperienced inspectors may overlook issues, reducing their effectiveness.
Tools Required for Manual PCB Inspection
For effective PCB inspection, some essential tools exist to examine the circuit board for defects and irregularities. Some of the most essential tools are as follows:
Use the magnifying glass or microscope to inspect the PCB and components visually. This tool can help identify small defects that could be impossible to see with the naked eye.
Well-Lit Lighting Area
A well-lit area is required to inspect the circuit board. The IPC-A-610 guidelines recommend 1000 lm/m^2. A properly lit working area helps to reduce eye pressure. It also ensures the defects are more visible during the inspection process.
Ensure you have proper documents from the client or the manufacturer. It helps to understand the design requirements and expect quality standards for PCB.
Probe and Pointed Tools
Probe or pointed tools can test the solder joints or components for solidity. It helps to identify the loose connections and poorly soldered components.
Dust, debris, or residues on the PCB surface can obscure defects. Cleaning tools such as brushes, cotton swabs, or compressed air can be used to remove any contaminants before Inspection.
Fixture or Holder
A fixture or holder can secure the PCB in place during Inspection, preventing it from moving around and ensuring a stable viewing position.
Use a marker or labeling pen to mark any defects or irregularities found during Inspection. This helps document the issues and aids in troubleshooting and corrective actions.
Personal Protective Equipment (PPE)
Depending on the nature of the PCB and any associated risks (e.g., sharp components, hazardous materials), appropriate PPE such as gloves, safety glasses, or anti-static wrist straps may be necessary.
How effective is PCB Manual Inspection?
Manual Inspection of PCB can be practical for identifying certain types of defects. The effectiveness depends on various factors, including the experience and expertise of the inspector and design complexity.
Below are some factors to consider regarding the effectiveness of manual PCB inspection:
Visibility or Defects
Manual Inspection effectively identifies visible defects like missing components, misaligned parts, solder bridges, and other solder defects.
Inspectors can use various tools to examine the components and solder joints and enhance their ability to detect defects.
Expertise and Experience of Inspectors
The efficiency of manual Inspection depends on the expertise and experience of inspectors. Experience technicians who are familiar with the PCB assembly process and common defects can identify issues accurately.
Complementary to Automated Testing
Manual Inspection is often used with automated testing methods such as automated optical Inspection (AOI) or X-ray inspection. While manual inspection can catch certain defects, automated testing provides greater accuracy and efficiency in detecting defects that are impossible to see with the naked eye.
In batch production, manual Inspection is often applied through random sampling, where a subset of PCBs is inspected rather than every individual board. While this approach increases efficiency, it also introduces the risk of missing defects that may be present in uninspected boards.
Manual Inspection has both advantages and drawbacks. Due to its simplicity, it is low in cost. It doesn’t require specialized equipment and devices. The inspection is quick and easy to add in any step.
The only thing required for this PCB inspection is the subject matter expert. At ElePCB, we use all the standard methods to inspect the circuit board. We have a team of experienced and skilled inspectors who can accurately identify any defects present in your circuit board.