Proportional Through-hole Padstacks

 

 

The first column is the Maximum Component Lead Size and it is determined by -

 

 

The second column is the Finished Hole Size and it is determined by adding 8 mil (0.2 mm) to the Maximum Lead Size in the first column. This is the "Nominal" Lead to Hole calculation as seen in the chart from the IPC-2222 standard.

 

 

The next 5 columns are the Pad Sizes for all the layers and they are the same value across all the rows. The Pad Size starts out using the IPC-2221 nominal annular ring requirements of 10 mil (0.25 mm) or the Pad is 20 mil (0.5 mm) larger than the hole size.

 

Then, as the hole size gradually gets larger, the pad annular ring grows "Proportionally" larger in increments of 1 mil (0.025 mm). The primary theory is that the hole size gets larger to accommodate a larger component lead. Larger component leads are created to carry additional current or because the component size is large and needs stronger support (more solder).

 

The Plane Anti-Pad Clearance is derived from the Hole Size and it remains relatively constant because it has nothing to do with supporting large components. It's simply a clearance from the hole to improve the PCB manufacturing yields. The minimum annular ring of the Plane Anti-Pad is 15 mil (0.35 mm) for holes intended for component leads. As the hole size grows in size, the Plane Anti-Pad stays somewhat constant but it does slightly grow as the hole size grows to keep a safe distance from higher voltage currents that larger holes can carry.

 

The Thermal Relief is a simple formula -

The ID is 20 mil (0.5 mm) larger than the Hole Size

The OD is the same value as the Anti-pad

The Spoke Width = Anti-pad X 75% divided by 4 spokes, the calculated spoke width X 4 = Hole Size or slightly larger than the hole