As PCBs advance towards higher levels of complexity and precision, the requirements for interlayer alignment accuracy have become increasingly stringent. Consequently, the issue of PCB layer misalignment has become more prominent. Various factors contribute to layer misalignment during PCB production. Here, we share some key factors affecting layer misalignment.
Definition of PCB Layer Misalignment
Layer misalignment refers to the deviation in concentricity between different layers of a PCB that are meant to align precisely. The required tolerance depends on the design specifications of the PCB type. The smaller the distance between holes and copper, the stricter the control to ensure conductivity and current-carrying capacity.
Common Methods for Detecting Layer Misalignment During Production
In the industry, the common practice is to add a set of concentric circles at each corner of the production board. The distance between these concentric circles is defined according to the layer alignment requirements of the board. During production, X-ray inspection machines or X-drill alignment machines are used to check the degree of offset in the concentric circles, thereby determining the layer misalignment.
Causes of Internal Layer Misalignment
Inconsistent Film Expansion and Shrinkage
Inner-layer films may expand or shrink due to changes in temperature or humidity during processing, causing misalignment.
Exposure Machine Misalignment
Misalignment during the exposure process can result in layer misalignment if positioning is inaccurate.
Operator Error
Improper handling during the alignment and exposure processes can also lead to misalignment.
Causes of Lamination Layer Misalignment
Inconsistent Core Board Expansion and Shrinkage
Variations in the expansion and shrinkage rates of core boards from different layers during processing can cause misalignment.
Defective Punching of Alignment Holes
Inaccuracies in punching alignment holes may lead to misalignment.
Fusion Misalignment
If the layers are not precisely aligned during the lamination process, fusion misalignment may occur.
Rivet Misalignment
Misalignment during the riveting process can lead to layer misalignment.
Sliding During Lamination
Sliding of the laminate during the lamination process can also cause misalignment.
Other Related Factors
Material Characteristics
Different PCB materials, such as FR-4 or high-frequency materials, may have varying shrinkage rates, which can lead to misalignment.
Process Control
Poor control of the manufacturing process can also result in layer misalignment.
Equipment Precision
Low-precision equipment used during manufacturing may contribute to misalignment.
Environmental Factors
Temperature and humidity fluctuations in the production environment can affect material shrinkage, resulting in layer misalignment.
Methods for Detecting Layer Misalignment
To detect layer misalignment, concentric circles are added to the four corners of the PCB. X-ray inspection machines or X-drill alignment machines are then used to measure the offset between these concentric circles.
Preventing Layer Misalignment
To minimize the risk of layer misalignment, PCB manufacturers must:
Strictly Control Production Processes
Ensure each step of the manufacturing process is carefully monitored and controlled.
Use High-Precision Equipment
Invest in advanced machinery to improve production accuracy.
Conduct Rigorous Quality Control
Implement strict quality control and inspection measures throughout production.
By addressing these factors, manufacturers can significantly reduce the occurrence of PCB layer misalignment and improve overall product quality.