Drilling holes in a circuit board

Understanding the PCB Drilling Process for Different Hole Types and Locations

One of life’s greatest joys is the satisfaction of knowing that you have built (or helped build) something with your own hands that others will use. Those types of memories never fade. Do you remember when your father, uncle, or employer finally decided that you were ready to graduate from gopher to actually using tools? More than likely, the first power tool you mastered was the drill. Although a simple device, this machine is essential for virtually any type of construction.

PCB construction is certainly an area where drilling is a critical part of the process. This is true whether your design is single-layer and only needs mounting holes or is a multilayer PCB that requires vias. In most cases, your design requires both of these, as well as other types of drill holes. Let’s explore the different types of drill holes and their uses, and then the PCB drilling process that your CM employs to ensure your built board precisely incorporates the drill holes that your board design requires.

Types of PCB Drill Holes

PCB drill holes can be classified according to whether they carry current or not. This categorization falls short of demonstrating the significance of drill holes within circuit board structures. A more thorough means of organizing or distinguishing between drill holes is according to their usage, as described below.

PCB Drill Hole Types:

  • Non-plated through-holes
    • Fasteners

These holes are used for mechanical justification or to ensure that an installed component that required additional support was installed correctly.

    • Mounting holes

These holes are typically for mechanical fasteners on installations where vertical clearance is not a major concern.

    • Countersink holes

Countersink holes are NPTHs that are used for mounting boards where the bolt head needs to be lowered below the surface.

  • Plated through-holes
    • Press-fit

Press-fit holes fit the leads of through-hole components and therefore do not require solder or fill.

    • Through-hole vias

These holes are for routing traces from the top to the bottom surface. However, as these conductors extend throughout the board stackup, they can also be used to route signals between any layers, as needed.

    • Blind vias

Blind vias provide an electrical connection between a surface layer and an internal layer of the stackup. In contrast to through-hole vias, blind vias only extend to targeted layers.

    • Buried vias

Connections between internal layers that do not extend to either the top or bottom surfaces are referred to as buried vias.

    • Microvias

Microvias may be blind or buried. What distinguishes them from other vias is their small size, enabling their use in high-density signal routing.

    • Thermal vias

The objective of thermal vias is not to conduct current; however, these critical PTHs leverage the high transfer rate of copper to remove excess heat, typically from a high-power component on the surface.

As shown above, vias are used in many ways. Now, let’s take a look at the PCB drilling processes for creating them.

PCB Drilling Process for Different Drill Holes

When designing the PCB layout, your CM’s DFM rules and guidelines should be optimized to ensure the highest quality manufacturing of your boards. Following these rules for drill holes is critical, as they are one of the most important elements of your board’s design and construction and are impacted by trace routes and widths, clearances, annular ring design and other board specifications. Additionally, holes must be precisely bored, and accuracy is directly related to the equipment and PCB drilling process methods that your CM utilizes, as shown below.

PCB Drilling Process Equipment and Methods

Drilling holes through circuit boards may be a common process, but it is also a delicate procedure that often requires specialized equipment. For most PCB manufacturing requirements, an automated drilling machine will suffice; although, these vary in capability among fabricators. Mill machines are also used due to their flexibility that allows for board shaping or the machining of other non-standard PCB form factors in addition to performing complex drilling operations. For small precision holes, such as microvias, laser drilling is employed. These three PCB drilling process options, along with the ability to back drill, are sufficient to create any drill hole that your design requires, as shown below.

Drill Hole Type Automated Drilling Mill Machine Laser Drilling
Press-fit O O
Mounting hole O O
Countersink (back drilling) O O
Through-hole O O
Blind O O
Buried O O
Microvia O
Thermal via O O
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As discussed above, PCBA operation depends significantly on the use of drill holes and the PCB drilling process options available from your CM. Tempo Automation, the industry leader in fast, high-quality board manufacturing, is capable of creating your boards with precise drilling for any holes that your design requires.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you would like more information on the PCB drilling process, contact us.

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