PCB Hole/PAD Through Hole

A pad is a small surface of copper in a printed circuit board that allows soldering the component to the board. There are 2 types of pads; thru-hole and smd.

Thru-hole pads are intended for introducing the pins of the components, so they can be soldered from the opposite side from which the component was inserted. The smd pads are intended for surface mount devices, or in other words, for soldering the component on the same surface where it was placed.

See the image:IC1 and R1 are SMD and Q1 and PW are Through Hole.

PCB PAD CALCULATION for Leaded Components:

To calculate the max pad Diameter of through hole components we have to go for 3 processes.

1.Find out the Maximum Lead Diameter:Firstly you should find out the maximum lead diameter. It is present in the datasheet or package drawing of the component. Lead sizes are in Round,square or in rectangle shape. Lead shapes images are given below.Rectangle or square shape hole diameter consider from diagonal.

2. Calculate the Minimum Hole Size:

Minimum Finished hole size the size of hole in which leads of the components can be easily inserted and Solder can easily flow through the lead.

Minimum Hole Size =Maximum Lead dia+Hole Diameter Factor

Minimum Hole Size = Maximum Lead Diameter + 0.25mm (for Density Level A )

Minimum Hole Size = Maximum Lead Diameter + 0.20mm (for Density Level B )

Minimum Hole Size = Maximum Lead Diameter + 0.15mm (for Density Level C )

* Density Levels A, B and C describe the measure of the relative ease of manufacturing.

Density Level A is used for General Design Producibility. It is a Preferred Level. Level A is used for the Low component density. In this case, footprint geometry is ‘Maximum’. This method is applied to the most robust producibility.

Density Level B is used for Moderate Design Producibility. It is a Standard Level. Level B conditions are suitable for reflow, wave, drag or dip soldering.

Density Level C is used for High Design Producibility. It is a Reduced Level. Level C is used for the High component density. In this case footprint geometry is ‘Minimum’. This method is applied to a hand-held and portable appliances.

Hole Diameter Factor Diameter factor details are as per IPC 2222 .

3. Calculate the Pad Diameter

After you calculate the Minimum Hole Size, you should know that the Minimum Annular Ring is0.05mm (50um). According to IPC-2221 the Minimum Fabrication Allowance is 0.6mm for Level A, 0.5mm for Level B and 0.4mm for Level C.

Pad Diameter = Minimum Hole Size[Finished] + Minimum Annular Ring X 2 + Minimum Fabrication Allowance

Pad Diameter = Minimum Hole Size + 0.1mm + 0.40mm (for Level A of IPC-2221)

Pad Diameter = Minimum Hole Size + 0.1mm + 0.25mm (for Level B of IPC-2221)

Pad Diameter = Minimum Hole Size + 0.1mm + 0.20mm (for Level C of IPC-2221)

Annular Ring:An annular ring is the area on the pad that surrounds the hole . The width of the annular ring is important design and manufacturing consideration. Generally we keep 10mils annular ring.

Anti pad: The anti-pad is the void area (shown as the blue annular ring in the diagram below) between the pad and the copper of the plane. Generally anti pad is 30 mils over to finished hole size.

Thermal Pad: A thermal relief pad is a printed circuit board (PCB)pad connected to a copper pour using a thermal connection. It looks like a normal pad with copper "spokes" connecting it to the surrounding copper. A pad directly connected to the copper pour is difficult to soldersince the heat quickly leaks away from the pad into the copper pour due to high thermal conductivity of copper. A thermal connection restricts the heat flow, making the pad easier to solder

See the below 2 images are there. One is filled copper pad another is thermal pad with 4 copper spokes connection.

A common plated through-hole pad stacks Chart is given below.