PCB annular rings, often a source of concern for designers, are the copper areas surrounding drilled holes on a PCB. Ensuring a centered via doesn’t guarantee the absence of tangencies or breakouts, highlighting the need for a deeper understanding of these structures. This article aims to shed light on the challenges and solutions associated with designing PCB annular rings, their significance in PCB functionality, and how to prevent potential issues.
What is a PCB Annular Ring?
Essentially, an annular ring is the copper region encircling a finished, drilled hole, specifically the through-hole copper plating. Adequate copper in this area is crucial for forming strong connections between the via and copper traces, particularly in multilayer PCBs, where annular rings act as anchors for the board and facilitate inter-layer connections. The minimum annular ring diameter is dictated by the capabilities of the PCB assembler, with the nature and plating of the hole influencing the diameter. Small annular rings pose a risk of via damage and breakouts.
The Structure of PCB Annular Rings
Mathematically, an annulus is the region bounded by two concentric circles. Similarly, a PCB annular ring is the copper area between the edge of the drilled via and the outer edge of the pad. Ideally, a wider annular ring ensures a better copper connection around the hole, mitigating the risk of breakouts.
Why Annular Rings Matter
Annular rings are vital for establishing reliable electrical connections on a PCB. Issues with annular rings, such as inadequate width or tangency, can severely impact trace continuity and the overall functionality of the board. Unfortunately, some designers overlook the importance of proper annular ring design, leading to potential problems. Accurate drilling is critical to avoid tangency, where the drilled hole touches the pad’s edge, further compromising board performance.
Common Problems and Solutions
Undesired Annular Rings: When pad size is small, the drill hole may consume excessive space, leading to an undesired annular ring. Prototyping can help identify and rectify such issues before mass production.
Tangency: If drilling is inaccurate, the hole’s edge may approach the pad’s edge, causing tangency. Precise drilling is essential to prevent this.
Breakout: Breakouts occur when the drilled via lacks proper encircling by the pad, often due to shifts during the lamination process. Maintaining an appropriate annular ring width is key to avoiding breakouts.
Annular Rings vs. Through-Holes
While related, annular rings and through-holes serve distinct purposes. An annular ring is the copper area between the pad and the via’s edge, providing connections for drilled vias. Through-holes, on the other hand, are mounting schemes for electronic components, involving leads inserted into drilled holes. Though an older technology, through-hole mounting remains relevant, especially for hobbyists due to its simplicity.
In Conclusion
Annular rings play a critical role in PCB functionality, acting as interconnect nodes between layers. Proper annular ring design is vital to ensure reliable electrical connections and overall board performance. By understanding the challenges and solutions associated with annular rings, designers can create high-quality PCBs that function optimally. Remember, partnering with a reputable PCB manufacturer like WellPCB can further ensure the production of boards with ideal annular ring widths and minimal risk of tangency or breakouts.
