PCB Minimum Annular Ring and Annular ring size

PCB  Minimum Annular Ring and Annular ring size

PCB minimum annular ring refers to the minimum amount of copper between the edge of the land and the edge of the hole, after the finished hole is plated. It is also referred to as a supported hole. Sometimes, the traces on a Electronic Circuit Board is required to be connected to another layer. In such cases, the traces end up on a pad. The via on the pad helps the trace to move from that pad and connect the other layer. The area on the pad, which surrounds the via is referred to as annular ring. It is very crucial to have a proper setting of the annular ring in the PCB layout software. This helps maintain proper spacing of copper. GWT is a company, which can help you in setting a proper annular ring for your Electronic Circuit Board.

Calculating The Annular Ring size

The copper ring, which is also referred to as the annular ring, makes a through-hole pad around a drilled hole. For the purpose of creating via, the drilled hole is surrounded by the ring of copper. In case of vias, this is most commonly referred to as outer diameter or via size. According to the IPC-2221A standard, the PCB minimum annular ring size is calculated as follows:

Minimum Annular Ring = (Min Ring Border) * 2 + (Hole Size) + (Tolerance)

--Minimum Annular Ring on the Inner Layer: 0.1mm

--Minimum Annular Ring on the Outer Layer:0.05mm 

Annular ring width can be calculated as (diameter of the pad - diameter of the hole)/2. So, for example, if the diameter of a pad is 20 mil and its hole diameter is 10 mil, then the annular ring width would be: (20 – 10) / 2 = 5 mils.

Why Does the Annular Ring Size Matter?

The size of the annular ring matters because it determines the success of your conductivity. While you don’t want it to be too wide since you’re working with a tiny space, you do need it to be wide enough to keep the connection strong. 

Figure 01-PCB Minimum Annular Ring

How to Get the Annular Ring Size Right？

Each PCB manufacturer will stipulate the tolerance for the annular ring through the PCB manufacturing process. However, to be on the safe side, you should always add a little more space. 

Most designers recommend increasing the size by 1.0mm from the manufacturer’s specifications. The slight extra width will help prevent any issues later on. 

The size of your annular rings will also depend on what you’re designing the board for. The Institute of Printed Circuit Boards specifies three categories for PCBs: Class 1, Class 2, and Class 3. Heavy-duty PCBs need larger annular rings because the via will be wider in diameter. Class 3 PCBs require more heavy-duty annular rings.