What is a loop

Ring ring is a technical term for the area between a hole drilled in a through-hole and the edge of a conductive pad. The through-holes act as interconnection nodes between the different layers on the PCB.

To understand the basics of annular rings, you need to know how to construct through-holes. In PCB manufacturing, the PCB is etched and removed by pads aligned with each other on different layers. Drill holes to form a hole and deposit copper on the wall by electroplating.

When you view the PCB from the top, the drilled through holes show a circular pattern. They are called rings. The size of the ring is different. Some PCB designers chose to use thicker loops, while others assigned thinner loops due to space constraints.

The size of the ring is calculated by the following formula.

Ring size = (diameter of backing plate – diameter of drill bit) / 2

For example, drilling a 10 mil hole in a 25 mil pad will produce a 7.5 mil ring.

Common problems with loops

Since the through-holes are an important part of PCB manufacturing, it is often assumed that the loops are error-free. This is a misconception. If there is a problem with the loop, it may affect the continuity of the trace.

Theoretically, a perfect ring is formed by drilling a hole in the center of the through-hole pad. In practice, the precision of drilling depends on the machine used by the PCB manufacturer. PCB manufacturers have a specific tolerance for the ring, usually about 5 mils. In other words, the borehole may deviate from the mark within a given range.

When the bit is not aligned with the mark, the resulting hole will face the side of the pad. Annular tangents appear when part of the hole touches the edge of the pad. If the borehole deviates further, leakage may occur. Leakage is when a portion of the hole exceeds the filled area.

Annular fracture can affect the continuity of the through-hole. When the copper area of the connection hole and pad is small, the current will be affected. This problem becomes even more apparent when the affected channels are used to deliver more current. When a ring break is detected, more copper filler is usually added around the exposed area to hold it in place.

In some cases, it can cause irreparable problems. If the hole is offset in a way that pierces adjacent wiring, the PCB will be accidentally short-circuited. This problem is difficult to resolve because it involves physical isolation through holes and short circuit wiring.

Correct ring size adjustment

While PCB manufacturers do have a responsibility to produce accurate loops, designers can play a role in setting the design to the right size. Allow more space outside the manufacturer’s specified tolerance range. Assigning an extra 1 mil to the size of the loop will save you trouble shooting later.