With the development of PCBs toward higher layers and higher precision, the requirements for interlayer alignment accuracy have become increasingly stringent, and the issue of PCB layer misalignment has become more severe. There are many reasons for layer misalignment in PCB manufacturing, and here we share some of the main factors influencing layer misalignment.
General Definition of PCB Layer Misalignment:
Layer misalignment refers to the deviation in concentricity between the layers of a PCB that are required to be aligned. The tolerance range is controlled based on the design requirements of different types of PCBs. The smaller the distance from the hole to the copper, the stricter the control to ensure its conductivity and current-carrying capacity.
Common Methods for Detecting Layer Misalignment During Production:
A common method in the industry is to add a set of concentric circles at each corner of the production board. The distance between the concentric circles is set according to the layer misalignment requirements of the production board. During the production process, the degree of concentricity deviation is checked using an X-Ray inspection machine or X-drill target machine to determine the layer misalignment status.
Causes of Inner Layer Misalignment:
- Inconsistent Film Expansion and Contraction: Inner layer films may expand or contract due to changes in temperature or humidity during processing, leading to layer misalignment.
- Exposure Machine Alignment Deviation: Inaccurate alignment during the exposure process may cause layer misalignment.
- Improper Operation: Improper handling by operators during the alignment and exposure process may also lead to layer misalignment.
Causes of PCB Lamination Misalignment:
- Inconsistent Core Board Expansion and Contraction: Different layers of core boards may expand or contract inconsistently during processing, potentially causing layer misalignment.
- Poor Punching of Positioning Holes: Inaccurate punching of positioning holes may lead to layer misalignment.
- Fusion Misalignment: Imprecise fusion during the lamination process may cause layer misalignment.
- Riveting Misalignment: Misalignment during the riveting process may result in layer misalignment.
- Slippage During Lamination: Movement of the board during the lamination process may cause layer misalignment.
Other Related Factors:
- Material Properties: Different PCB materials, such as FR-4 and high-frequency materials, may have different expansion and contraction rates, which could also lead to layer misalignment.
- Process Flow Control: Improper control of the process flow throughout PCB manufacturing may cause layer misalignment.
- Equipment Precision: The use of low-precision equipment may result in layer misalignment.
- Environmental Factors: Changes in temperature and humidity in the production environment may affect material expansion and contraction, thereby causing layer misalignment.
Methods for Detecting Layer Misalignment:
Add a set of concentric circles at the four corners of the PCB and use an X-ray inspection machine or X-drill target machine to detect the degree of deviation between the concentric circles.
To avoid layer misalignment issues, PCB manufacturers need to strictly control the production process, use high-precision equipment, and implement rigorous quality control and inspection during production.