Inserting component pins into through-holes and soldering them on the other side is a common practice, enhancing the connection between components and PCB. However, this approach poses two significant issues: electromagnetic interference caused by excessively long pins and space wastage due to traversing the entire board. As the electronics industry flourishes, the demand for multifunctionality and reliability has intensified. Traditional through-hole designs are no longer sufficient to meet these requirements. Consequently, blind vias have emerged to significantly promote the development of miniaturization. So, what are blind vias, and how are they manufactured?
What Are Blind Vias in PCB
Essentially, blind vias are one of many PCB vias, primarily designed to connect different layers of the PCB. Visually, blind vias are open on one end only, eliminating the need to traverse the entire PCB. A simple analogy would be pouring water into an opening without it flowing out from the other side.
From the definition of blind vias, we can discern that their manufacturing presents significant challenges. The main challenge lies in precisely controlling their depth to achieve the desired interlayer connection. To accomplish this goal, manufacturers need specialized equipment. Due to a higher failure rate, manufacturing costs are often elevated. Therefore, in practical applications, not all components are connected to the PCB via blind vias. They are primarily used for BGAs and other small chip package components.
Benefits of Adopting Blind Vias Design
One noteworthy advantage is the suitability of blind vias for miniaturized and high-density designs. Components are connected to the PCB via circuit traces, and for more complex projects, multilayer PCB is usually required. Blind vias allow the connection of circuits on internal layers to circuits on external layers, optimizing PCB surface area utilization without traversing the entire board. These advantages enable blind vias PCB to accommodate more components within the same footprint.
Furthermore, blind vias are highly compatible with advanced technologies like high-density interconnect (HDI). By creating an HDI structure, multiple layers of circuits can be combined into a single layer, saving space and reducing costs. While blind vias and HDI concepts often coexist, it does not imply necessity. However, blind vias allow designers to be more flexible when arranging components in building HDI PCB.
Another crucial aspect is that using blind vias during PCB drilling significantly improves product reliability. This is reflected in several aspects, such as reducing electromagnetic interference by shortening pins, using more advanced drilling equipment to minimize burr formation, and allowing designers to optimize the paths of signal traces without the constraints of traditional through-hole designs.
Despite the advantages, it is essential to be aware of the drawbacks of PCB blind vias, with the most obvious being their manufacturing cost. The most common method for manufacturing blind vias on PCB is laser drilling. While laser drilling allows for more precise drilling, the equipment is often more expensive, leading to higher manufacturing costs for the manufacturers who need to invest in them. Additionally, these extra costs are passed on to the users, thereby increasing the overall project cost.
On the other hand, blind vias can complicate repairs, both during manufacturing and in later use. If the drilling depth is excessive, it may penetrate layers that should remain unaffected, and this fault is often irreversible. Moreover, in post-assembly board usage, if a component failure occurs, removing it may lead to pins remaining in the hole due to the absence of pin protrusion from the other side, increasing the difficulty of subsequent repairs.
How to Create Blind Via PCB
When determining that your project indeed requires blind vias on the PCB, you need to start from the design phase. You can choose suitable design software, such as Altium, Eagle, KiCad, or any other software that includes setup options. Taking Altium Designer 17 as an example, you can find relevant details in the “Layer Stack Manager.”
Follow design specifications during the design phase, such as avoiding blind vias occupying an odd number of layers, starting from the top or bottom layer, and absolutely avoiding ending in the core or center. After completing the design, use the software’s built-in verification tools to validate compliance. Export the design files and submit them to the PCB manufacturer for production. It’s crucial to emphasize that the manufacturing capabilities of the manufacturer you choose must match your design, including minimum hole diameter, hole pitch, etc.
Typically, drilling occurs after lamination, when the basic outline of your PCB has been constructed. For drilling, it is advisable to use laser drilling for blind via drilling, as it not only improves drilling accuracy but also results in smoother hole walls. Hole diameter and depth are usually interrelated, with larger holes requiring greater depths. Finally, check the quality of blind via drilling.
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