In computing and electronic devices, the conduction of a circuitry is done by a green board, which transfers different signals to the screen from its control prompts. In all smartphones, you will find a printed circuit boards in it with different components and chips. This helps in conducting signals for the thousands of commands and features of the device.
Anytime you push any of the touchscreen’s prompts, you are automatically activating one of the internal board’s signals. The conduction of majority of these signals is done through via PCB. Let’s go into more details about what via PCB is all about, types of via, the importance of via in pcb design and more.
Via PCB: What does this Mean?
In PCBs, vias are referred to as holes passing through the board layers to ensure conductivity. Each of these holes serves as a path that allows electrical signals to pass through circuit layers. There are varying levels through which vias travel on a PCB.
Depending on the PCB design, the board may require holes that pass through the layers. Some vias pass through only the bottom and top layer, while some pass through the inner layer. Concerning vias on PCBs, different options are available.
Vias are included among one of the most important features on PCBs. They make up a fairly large fraction of the necessary cost of board manufacturing. Despite that these vias serve one major purpose, just one type of via will be suitable for some PCB designs. Let’s go on to talk about the different available types of via in PCB design, as well as how each of them facilitates connections on PCBs.
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Types of Via in PCB Design
Depending on the location of vias in PCB layers, two major categories exist. These include the buried and the blind hole.
For blind hole, its hole passes through the board’s bottom or top layer and then stops before getting to the internal layers. They are called blind holes because when you hold the board up to face light, you won’t be able to see through it.
The process dealing with the creation of the blind-hole could be hard because you have to know the exact time to stop the drilling of the board. This is the reason why many via PCB manufacturers usually don’t want to hole plate this type.
The other type of via in PCB design is called the buried hole. This may appear via internal layers (one of more). Since this type is usually sandwiched between the layers, you won’t be able to see it with your naked eyes.
For blind-layer multilayer boards, the internal layer’s hole plating has to be finished before time during the PCB assembly. After then, you can apply the bottom and top layers onto the board. You can placed the via through any of these main types
Through-hole
Through-hole is the most obvious of all the types of via PCB. This penetrates the layers of multilayer boards. Compared to buried and blind holes, through holes are larger. You can also identify them easier with the eyes.
This technology has been in existence since the middle of the 20th century. This period, it came to replace point-to-point construction. From the 1950s to the 1980s, the Through-holes became the most common. This time, almost all the PCB features had an attachment to a through-hole.
During its early days, the tracks of PCBs were only printed on the top area. However, as advancement in technology increased, the printing started appearing on the two sides. Now, plated-through holes helps in connecting the different PCB layers. Furthermore, through-holes are useful in facilitating components having wire leads.
You can find through-holes on large motherboards, which were utilized in computer towers all through the 1990s and the 2000s. Furthermore, you can also see printed circuit boards having through-hole components in old PCI cards, which were plugged to the older motherboards. You will also find similar features on graphics cards, which predate the flat-screen all-in-one devices of today.
The way compact, small, electronic gadgets and mobile devices are gaining popularity today, printed circuit boards are either designed with a few or no through-hole component. Therefore, there are few reasons why PCB designers keep making use of boards, which contain through-holes that are large, as they take up so much of the board’s space. This could have been used more efficiently with microvias.
The fact is, for designers to ensure their boards remain small, they must make sure that surface mounts and microvias are used more frequently. As this trend continues, in years to come, through-holes may likely be discontinued.
Via in pad
This type of via involves applying vias on ball grid array pads. Via in pad involves placing vias on the BGA pads of the circuit board. This design is popularly applied since it reduces the required space for vias. Therefore, via in pad enables PCB manufacturers to design smaller PCBs that need less space for signals routing.
The via in pad design is an effective technology for compact electronic devices. These devices have been designed to fit small spaces. The via in pad design enhances routing. This is because the holes directly link up to the layer underlying the component. Therefore, signals can route without going beyond the perimeter of the device.
However, some PCB manufacturers don’t place vias on BGA pads. This is because of the drawbacks of the via in pad technology. One of which is that you have to fill up the pad with copper. If not, the solder will come off the pad and the circuit board will lose connectivity.
Another drawback is that vias involve a time-consuming step. Some manufacturers don’t want to add this to the cost of manufacturing a PCB. Also, vias can alter the drill diameter when placed in a pad.
Although there are drawbacks to placing vias on BGA pads, there are some advantages to it. With via in pad technology, you can create smaller circuit boards. The via in pad PCB might be the only option for modern mobile devices.
Solder masks can prevent the flow of solder into the via in a via layout. Manufacturers need to fill in the vias when placed in BGA via in pad. Also, a flat planar surface is very important as this can help to connect fine-pitch BGAs.
Microvias
Vias below 150 microns are microvias. Manufacturers use these microvias on several high-density interconnect PCBs. Microvias are more preferred because of the small hole size that takes less space on the PCB. Copper plating helps to connect the layers to one another.
Microvias are available in a cone shape. This ensures it is easier to plate the vias’ sides with copper. A microvia can’t go through more than two adjacent layers. You would have to stack many microvias if a PCB design needs a via through several layers.
Manufacturers confirmed that the creation of stacked microvias can be a time-consuming process. Also, it can be very costly. PCBs that need one microvia over the other will feature two microvias. The limit for stacking is four microvias. Manufacturers rarely apply four microvias due to the high costs. The staggered microvia is the alternative option to the stacked microvia. However, staggered microvias are difficult to make on a multilayer circuit board.
A blind microvia occurs when a microvia passes through the board’s outer layer and cuts to an inner layer before it stops. Manufacturers increase the wiring density on a PCB with the help of blind microvias. These microvias are beneficial if you must route a signal on the outer layer to an underlying layer. In this case, the blind microvias will provide the shortest distance.
Also, blind microvias can maximize space in a multilayer PCB. In some scenarios, a microvia will pass through two layers. Such blind vias are referred to as skip vias. Manufacturers don’t recommend skip vias due to the nature of the hole.
A buried microvia is one that links up two inner layers in a circuit board. Manufacturer s must drill the layers with the holes before applying the outer layers.
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Importance of Vias in PCB Design
If you are designing a simple PCB, vias might not be important. However, you will need vias when designing multi-layer boards. Vias offer a lot of benefits in PCB design. Here are some:
- Vias increase the density of trace in multi-layer PCBs. You can run these vias over and beneath one another in several directions. Vias enable different traces to connect with each other. Therefore, they function as vertical connection factors.
- Vias enhance signal and power transmission between PCB layers. Route PCB components on a single plane if you plan not to incorporate vias in your design.
- They create a great component density in multilayer PCBs.
- Vias offer multiple connections to a plane on a PCB. For instance, strip of metal with vias may surround a sensitive area on a circuit board. This provides EMI protection
Via PCB Sizes: Which is the Right Size?
Always make sure you consult your manufacturer for their least annular ring and drill size they plan to use for the whole process.
Normally, without any frequent breakage, mechanical drills do not go below 12 miles in diameter. For cases of frequent breakage, the manufacturer will have no choice but to raise the cost to cover for the broken drills.
For the standard processing, annular rings usually don’t go less than 6 miles. Therefore the smallest possible via you can create has a diameter hole of 12 miles and a diameter pad of 24 millimeters. This means that the size of the pad must be twice that of the hole.
Making a Via in Printed Circuit Boards (PCBs)
Making a via is best during the design process of circuit boards unless you possess a DIY Via Rivet gun. First of all, drill holes through your board’s copper pads.
Secondly, on the holes you’ve drilled, apply a specific chemical. This helps in liquefying the epoxy present in the inner layers of your printed circuit board. In addition, this further uncovers the copper pad inner layers.
Lastly, add some copper to these holes through electro-coating.
Majority of manufacturers of circuit boards usually place some sacrificial vias on some design board parts. Next, they slice them and scan its cross-sections in order to determine the electro-coating process’ efficiency.
Determining the Right Requirements for Via on PCB
The size and purpose of a circuit board should determine the type of vias for a PCB design. If the PCB is for use in older and larger computing device, you need a PCB design that works with older standards. Any modern design will likely not match the device. Therefore, for these older devices, you need a larger board with THT components.
If your PCB is for use in a smaller device, you don’t need through-hole components. This is because you will need to optimize the small space on the tiny circuit board. For instance, if a PCB design is a square inch, there won’t be space for a big through-hole. This is because there are several signals to function well in the small space.
Therefore, such a board will need blind microvias. This microvias transfer strong signals between short distances on a tiny board. The process of fabricating smaller boards with microvias is a large investment. However, the benefits of these boards compensate the investment. This is certainly beneficial when you are designing a groundbreaking device.
Conclusion
Vias are important in PCB design. These metallic line holes carry out electrical signals between PCB layers. Manufacturers understand the role of via in pad technology in multi-layered boards. Hence, you must understand how they work. Vias are available in various types.
The application requirement of a board will determine the type of vias you opt for. Unarguably, the via in pad technology plays a vital role in both PCB design and manufacturing. It is important to incorporate vias when fabricating compact and complex PCBs.
