Annular ring's explanation provided by a PCB production specialist
In the realm of electronic components, annular rings play a crucial role in ensuring a robust and reliable connection. These copper bands surround drilled holes in multi-layer printed circuit boards (PCBs), providing an area for connecting leads or wires, and serving as an anchor for the circuit.
The primary function of an annular ring is to establish a good connection between a via and the copper trace. This connection is vital in preventing tangencies or breakouts, which can compromise the circuit's current-carrying capacity and reliability.
When it comes to the optimal annular ring width, recommendations suggest a minimum of 5 mils (125 microns) or more to meet IPC Class 2 reliability standards. This width balances mechanical robustness, electrical connectivity, and manufacturability of vias and pads.
It's essential to maintain a sufficient difference between the pad diameter and the drill hole to prevent the copper from touching the edge of the pad. A common practice is to have a pad diameter at least 0.1 to 0.15 mm larger than the drill hole, providing an annular ring width of about 0.05 to 0.075 mm on each side.
Incorporating tolerances in the design can account for potential mechanical or thermal stress during manufacturing and operation. Minimum conductor width in the annular ring area should maintain at least 50 microns (0.05 mm) and the copper reduction due to breakouts in this area should not exceed 20% of the minimum conductor width.
For users seeking guidance on PCB design, resources such as the Design for Manufacturing Handbook and the Better DFM tool offer valuable insights. The Better DFM tool even allows users to set minimum annular ring width requirements based on their needs, with options for 5 mil, 6 mil, 7 mil, and no minimum width (though this is not recommended).
In addition to annular rings, teardrop pads can be used to increase structural integrity, especially in flex PCBs. These pads add additional copper at the junction of annular rings with PCB traces, increasing structural integrity against mechanical or thermal stress. However, they are not necessary for conductors bigger than 20 mil.
In conclusion, maintaining annular rings of at least 5 mils, with appropriate drill-to-pad clearances, provides the best balance of manufacturability, mechanical strength, and electrical reliability for printed circuit boards. For further advice, users can refer to resources such as the Design for Assembly Handbook and the Better DFM tool.
For those designing annular rings, the SierraConnect PCB forum offers a platform where users can post their queries about designing annular rings and have them answered by experts. By adhering to these guidelines, designers can create PCBs that are not only cost-efficient but also reliable and durable.
Technology plays a significant role in the design and manufacture of printed circuit boards (PCBs), as annular rings – thick copper bands surrounding drilled holes – are essential for establishing robust and reliable connections between vias and copper traces. Adhering to recommended annular ring widths, such as a minimum of 5 mils, ensures mechanical robustness, electrical connectivity, and manufacturability of vias and pads, thereby contributing to the overall reliability and durability of the PCBs.
