Differences and Techniques in Copying 4-Layer vs. Multilayer PCBs Core Principles of Multilayer PCB Copying and Detailed Explanation of Sandpaper Grinding Delamination Technology

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I. Basic Logic of Multilayer PCB Copying

The essence of copying a multilayer PCB lies in deconstructing its complex internal structure into combinations of multiple double-sided boards. For example, a 4-layer board can be regarded as the superposition of two double-sided boards, a 6-layer board as three double-sided boards, and so on. The primary challenge in copying multilayer boards stems from the invisibility of internal traces, which necessitates delamination techniques to expose the internal circuitry.

II. Choice of Delamination Technology: Advantages of Sandpaper Grinding

Delamination is the core step in visualizing the internal layers of a multilayer PCB. Common methods include chemical corrosion and blade stripping, but these often risk damaging internal traces or losing data due to over-processing. Practical experience has shown that sandpaper grinding is currently the most accurate, economical, and widely adopted delamination solution.

III. Key Operational Points of Sandpaper Grinding

Tool Preparation: Ordinary sandpaper available at hardware stores is sufficient.

Operation Process: Typically, lay the PCB flat, hold the sandpaper, and grind evenly across the PCB surface.
For smaller boards, the sandpaper can be laid flat with the PCB placed on top (or vice versa).
Apply even pressure and grind repeatedly in the same direction. For very small boards, use fingers to press and move the PCB against the sandpaper.
The key is to maintain a flat surface and ensure uniform grinding.

Grinding Effect: The silkscreen and solder mask layers usually wear off quickly, while copper traces and planes require additional grinding.
Time Reference: Bluetooth boards take a few minutes, while memory modules may require over ten minutes.

IV. Specific Steps for Copying a 4-Layer Board

Surface Layer Scanning: Scan the top and bottom layer images of the 4-layer board.
Surface Layer Copying: Complete the replication of the top and bottom layer circuits.
Grinding Delamination: Use sandpaper to grind away the top and bottom layers, exposing the two inner layers.
Inner Layer Scanning: Scan the images of the exposed inner layers.
Inner Layer Copying: Add the inner layers in the copying software and replicate their circuitry.
Final Inspection: Cross-check each layer’s traces to ensure copying accuracy.
Note: PCBs with more layers can be processed similarly, with workload increasing proportionally to the number of layers.

V. Key Techniques and Precautions for Multilayer PCB Copying
Cost and Risk: The manufacturing cost of multilayer boards is significantly higher than that of double-sided boards (often several times higher). Additionally, internal trace errors are difficult to repair with jumpers.
Prioritize Accuracy: Strictly verify the circuitry of each layer during copying to avoid minor errors causing complete board failure.
Experience Accumulation: Mastering the pressure and uniformity of sandpaper grinding is essential for ensuring delamination quality.
By following the above methods, the technical challenges of copying multilayer PCBs can be effectively addressed. However, attention to operational details is crucial to mitigate risks and ensure the reliability of the final outcome.

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