Through holes are holes that pass through something, commonly used in PCB manufacturing for installing components. Through-hole soldering creates stronger mechanical bonds than surface mounting, but drilling makes boards more expensive and limits routing. Other components, such as capture pads and annular rings, ensure signal integrity. CAD software is used to design pad stacks accurately.
A through hole is any hole that passes through something, whether it is milled or drilled using hand tools or sophisticated machinery. The most common type is the plated hole used in printed circuit board (PCB) manufacturing. Hole plating makes it easier for electrical signals to pass along the PCB, but it is not necessary to plate a through hole if it will be used for mounting other hardware.
These holes are used for installing various components on a circuit board, such as capacitors or any type of component that is pinned in. The ends of these parts are bonded to the pads on the underside of the PCB during the through-hole soldering process, which is a molten metal soldering procedure using reflow or wave soldering equipment. This type of mounting is advantageous because the resulting mechanical bonds are stronger than other techniques, such as surface mounting.
The through-hole design results in more expensive boards due to the required drilling and limits the total PCB area for routing signal traces. With multilayer boards, this is a problem because the holes go through all the layers of them. Placing the holes too close together can create problems with how signals are transmitted from one end of the board to the other.
A through hole on a PCB must have various other components to ensure that the integrity of the signals is not compromised. The capture pad, placed on the outer or inner layers of the board outside the hole, connects the traces to the plated through-hole so connections can be made to other components. Other elements include a copper ring larger than the shadow of the hole, known as an annular ring, which is where the through hole passes through each layer of the board. The finished hole diameter defines the size of the hole drilled, while the hole diameter reflects the size of the hole plus the copper plating versus the space occupied on the board.
PCB manufacturers use computer aided design (CAD) software to accurately model and create each through hole. The hole, capture pad, tip size, and plating are referred to in this software as pad stacks. These elements are designed using complex calculations to make sure that the circuits are made correctly and work as intended.
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