One of the most common mistakes made during PCB manufacturing is the improper hierarchical order, which can cause the whole process to fail. The PCB assembly process can work from an electrical continuity point of view, even through electrical inspection. In design, the order of the plane and the signal layer and the distance between adjacent layers are important.
In order to ensure that the production information is needed to perform the correct visual inspection of layer processing, PCB designers need to design the correct copper characteristics into the manufacturing data, that is, to achieve the proper cascade order. These copper features provide a mechanism for inspecting the final components, once the internal Q&A checks are carried out, which are cleaned up to the manufacturing facility.
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Layer recognition?
The first function of the copper added to each layer is to identify the layer order relative to all the other layers. Each layer receives a layer number etched directly into the copper, which indicates its position in the cascade, and the layer number must be included within the area of the finished plate. Layers should be located near the edge of the board so as not to interfere with the electrical characteristics of the circuit. It can take the form of a single number on each layer. But the numbers may not stack up. When all check charts are stacked, they must be clearly visible when viewed from the top down.
Layers are usually placed in rectangular boxes for easy identification. Remove the welding mask and screen function from the area around the layers to facilitate viewing the layers through the complete PCB through the inspection light source placed behind the assembly. Layers cannot be connected to any layer on the copper function, such as the power layer or polygon.
How to ensure the correct stack in PCB design
The number of layers etched into each layer of copper geometry
How to ensure the correct stack in PCB design
Shows the number of layers removed by solder mask for visual inspection
PCB stack and test rails?
How to ensure the correct stack in PCB design
Edge view of stacked stripes and test traces
How to ensure the correct stack in PCB design
PCB stacks are copper features at the edges of the PCB to facilitate visual inspection of hierarchical order. When the PCB is routed from the panel, the geometry must extend outside the edge of the board to expose the copper. The appropriate lamination geometry can be seen by observing the stacked stripes at the edges of the finished panels.
The purpose of the test track is to verify the post-etched copper thickness and width on each layer in the lamination. The test trace shall be 50mil in length and 5mil in thickness, and must extend beyond the edge of the board so that the copper is exposed when the PCB is routed from the panel. The edge view of the test trace can be measured with an examination microscope. This function is critical in designs with impedance-driven geometry.
How to ensure the correct stack in PCB design
Stripe size and test trace are drawn on the film layer
Note: Stacked stripes and test rails should not be connected to any surface such as the power plane or polygon copper features.
