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PCB Drilling: Important Step in PCB Manufacturing

After lamination, the PCB manufacturing moves on to the drilling stage. PCB drilling is the most critical and time-consuming stage. Due to the increasing density of electronic components and their continual downsizing, the PCB drilling process has become increasingly more complex and crucial. In the case of single-side or double-side PCBs, drilling is done right away after PCB cutting; however, in the more typical scenario of multilayer PCBs, the drilling phase follows the lamination process. We will discuss more details about PCB drilling in today’s blog.

What is PCB Drilling?

Making holes, slots, and other cavities in an electrical circuit board is called PCB drilling or printed circuit board drilling.  This procedure makes installing components and linking electrical nets between different PCB layers easier.
The PCB drilling process lays the foundation for vias and layer interconnectivity. The shrinking of electronic products such as TVs and smartphones has sparked the transition from stationary to portable PCB drilling. Advanced micromachining is required to reduce electronics’ dimensions, and the drilling technique is crucial to reducing the number of devices.
 
Drilling is a costly and time-consuming process in the manufacture of PCBs. Additionally, you must be extremely careful because even a small error could negatively affect the PCB’s quality. Therefore, PCB manufacturer’s capabilities are critical for someone who needs PCB products. FC takes center stage in PCB manufacturing and assembly industries. You can cooperate with us!

Types of Holes in PCB

As mentioned, we know what PCB drilling is. The purpose of drilling is to drill holes in the board material, the location and size of the holes should meet the customer’s requirements. It can realize layer-to-layer conduction and future component insertion welding. It also makes positioning or alignment holes for post-process circuit board processing. Therefore, there are different hole types in PCB. They are given below:

Classification by function

Foremost, the holes are categorized according to their purpose and function: via holes, component holes, mechanical holes, slot holes, and back drill holes.

Mechanical Holes

Typically, a PCB has mechanical components attached to it, such as connections, fans, and brackets. These items require holes to be mounted. Even though metal plating rarely occurs in these holes, it might if the mounted device needs an electrical connection to the PCB, such as a chassis ground. 

Via Holes

Tiny metal-plated holes can be applied to transfer ground, power, and electrical signals through the PCB layers. Depending on the specifications, these holes are known as vias. They provide electrical connections between various PCB layers, helping pass the power and signal through the board.

Component Holes

Even though surface mount components are mostly used for separate, inactive PCB components, most still work well with through-hole packaging. These parts consist of switches, connectors, and other mechanical parts that must be firmly mounted, which a through-hole package ensures. Furthermore, due to their ability to transfer heat and current, these packages are ideal for power components such as large resistors, capacitors, op-amps, and voltage regulators.

Slot Hole

The drilling machine’s drilling program is automatically converted into a collection of multiple single holes or through the milling method of processing out of the slot, generally used as a plug device pin installation, such as the oval pins to connect to the socket.

Back Drill

A hole with a certain depth (larger than the front-plated hole) drilled on an already plated through-hole, is used to block the stub of the through-hole and reduce reflections in the signal transmission process.

Classification by Electrical Connection

Depending on whether it is connected to an electrical appliance, it is categorized into PTH with plated holes and NPTH without plated holes.

PTH(Plated Through Hole)

Plated Through Hole (PTH) is a type of hole whose walls are plated with metal. It enables electrical connections between conductive patterns on the inside, outside, or inside a PCB. The size of the hole is determined by the size of the drill hole and the thickness of the plated metal layer

NPTH(Non-Plated-Through-Hole)

A non-plated-through-hole (NPTH) is a hole not involved in the electrical connection of the PCB, i.e. non-metalized. According to the level of holes through the PCB’s inner and outer layers, the holes can be divided into: through holes, buried holes, and blind holes.

Drilling in PCB Manufacturing Process

We know that drilling holes is after the press-fit of PCB manufacturing. Let’s look at the specific steps of how it is done next.

Mechanical Drilling Process

 Here are the six steps of machine drilling:
Step 1: Pinning
Nail the pins on the board’s edge, then the product can be fixed in the drilling work platform.
 
Step 2: Boarding
Stack and secure matting, plates, and foils in the specified order on the drilling platform.
 
Step 3: Drilling
Call up the drilling belt information, line up the knives, and then drill the holes for the finished products.
 
Step 4: End of shift
After drilling the holes, dismantle the pads, plates foils, etc.
 
Step 5: Back pin
Next, pull out the nails around the edges of the boards to make it easier to work behind them.
 
Step 6: Hole checking (AVI inspection)
Finally, an auxiliary inspection tool or automatic hole checker is adopted to check the drilled holes.

Laser Drilling Process

As for laser drilling, due to the difference in drilling equipment, the process is less uniform, the industry is mainly to infrared light, ultraviolet light to distinguish. The infrared light is represented by COz laser drilling machine, and the ultraviolet light is represented by UV laser drilling machine.
Step 1: Pre-drilling treatment
The copper surface is treated to improve the copper’s ability to absorb infrared light for direct ablation.
 
Step 2: Laser drilling
Ablation of copper for a different dielectric layer to create the desired hole.
 
Step 3: Hole checking (AVI inspection)
An automatic hole inspection machine is used to inspect the drilled holes.

Drilling Methods

A manual or laser PCB drill is typically used to drill holes due to the need for accuracy. Additionally, boards can be automatically or manually fed into a drilling rig. The different drilling methods are given below:

Laser Machine

It’s a delamination-free drilling technique. The technology was created to solve small hole sizes. A printed circuit board comprises three fundamental components: glass fiber, copper, and resin. These materials vary in composition and optical characteristics. This makes it difficult for a laser beam to pass through a circuit board precisely and effectively. Occasionally, conventional boards have narrow laser beam holes. For this reason, tiny blinds and buried vias are the primary uses for laser machining.

Vibration Drilling

It is a subset of vibration cutting that is unlike traditional drilling. The first is a pulsed intermittent cutting technique made possible by piezoelectric crystal oscillators, whereas the latter is a regular cutting process. With the same drilling conditions, vibration thrust and torque are 20–30% less than typical values. Vibration drills improve cutting stability and reduce burr, but they also cause other problems.

Automated Drilling Machines

It uses a computer to regulate every process step to create holes in PCBs. CNC machines are the most efficient automated drilling machines. It saves time and production costs when you need to drill multiple holes of different sizes and dimensions.

Mechanical Drilling

Mechanical drilling is appropriate for making through-holes in motor protection circuit breakers (PCBs) due to the requirement for increased accuracy, low temperature, and deformation.

Drilling Parameters and Considerations

There are different drilling parameters to consider. They are given below:

Aspect Ratio (AR)

It is the characteristic that determines PCB dependability. AR in a through-hole printed circuit board refers to the ratio of the board thickness to the diameter of the drilled holes. It is the ratio of the drilled hole’s diameter to its depth in the case of micro vias.AR denotes the capacity to deposit copper swiftly within the vias. Reducing the diameter and increasing the depth will make it more difficult to plate copper inside the hole. A copper plating bath that can throw liquid farther is necessary to deposit copper in the tiny holes. Divide the board thickness by the via’s diameter to find the AR of a through-hole. Micro vias can not pass through the entire PCB, hence their AR is determined by dividing the drill depth by the via’s diameter.

Drill-To-Copper

It separates copper objects from the edge of the channel. A copper trace or any other active copper area can be the object. It is important because circuit disruptions can result from even small deviations.

PCB Drilling Hazards

After repeated use, drilling tools tend to wear out and break. This can lead to the following problems.
 

1. Accuracy of hole position is affected

Accuracy is compromised when the drill fails to hit the preferred point and moves along the same axis. If the drill is offset, it can cause the hole ring to tangent or break.

2. Roughness in the drilled hole

If the material is rough, it will lead to uneven copper plating, which will leak the air into holes and roller cracks. Copper plating solution penetrating the hole wall will also lead to a drop in insulation resistance.

3. Resin coating

Due to the heat generated during the drilling process, the resin in the board melts. The resin sticks to the hole wall and is called resin smearing. This again results in poor copper plating and leads to conductive failures between the through holes and the inner layers of the circuit. We can remove resin stains with a chemical solution.

4. Presence of entrance and exit burrs

Burrs are unwanted portions of copper protruding from the holes after the drilling process, they are mostly found on the top and bottom surfaces of the printed circuit board stack.

5.Nail head

If the nail head is not suitable, the inner layer of copper may be bent when drilling. These copper bends will lead to uneven plating and result in conductivity problems.

6. Separation of layers

Partial separation of circuit board layers is considered delamination, and improper drilling can lead to delamination.

Remedial measures for drilling

1. Resin removal process

This is a chemical process used to remove the melted resin deposited on the hole wall. The process eliminates unwanted resin and enhances electrical conductivity through the through-hole.

2. Demurring process

This is a motorized process that removes the raised end (crown) of the metal (copper), called the burr. Whatever debris remains in the hole will be eliminated by the demurring process. The demurring process is repeated once more after demurring.

3. Delamination

This can be avoided by using laser drilling. In laser drilling, the workpiece and the tool do not come into contact, thus eliminating delamination.

The best practices for PCB drilling are given below:
  • It is best to keep the AR low to avoid drill wear.
  • The more drill bits you need to use, the more distinct drill sizes are in a PCB design. To cut down on drilling time, you can limit drill sizes instead.
  • Check to see if the drills that aren’t plated are connected.
  • Verify the number and size of drills in the drill file compared to the fabrication print.
  • Verify whether the type of drill is PTH or NPTH.
  • Verify that the holes on your board are smaller than 0.007. If any are discovered, you can either separate them or, if it’s feasible, remove some of them.
  • Verify if perforated breakaway tab mouse parts are accessible. They resemble the holes encircling a coupon and form a line of tiny holes in a printed circuit board. Mouse bits offer a better grip.
  • Verify if the copper layer features and associated drills are positioned outside the PCB profile.
  • The minimum spacing between the hole (edge) and PCB profile should be 0.01.
  • Once drilling tolerances have been considered, it is determined if the through-hole size needs to be reduced to meet the minimum AR requirement.
  • The tolerance for plated holes should be less than +/- 0.002, and for non-plated holes, it should be less than +/- 0.001.
  • Verify if the arcs fabrication drawing shows NPTH drill or cut-out locations but is missing the drill.
  • Give the appropriate sizes to be filled.

Conclusion

The PCB drilling industry is an exciting and ever-changing field. The process starts with a computer design and finishes with a circuit board integrated into the everyday electronic devices we depend on. The fundamental step in this procedure is PCB drilling, which is crucial to the dependability of these gadgets’ operation due to their accuracy and precision.
As the needs of the electronics industry continue to change, so do all PCB drilling technologies. Developments such as automated tool changers, laser technology, and high-speed drilling are shaping the future of PCB fabrication.

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