The increase in the demand for PCB miniaturization has resulted in the design of very complex PCB layouts. Complex PCB layout usually involves inserting holes in BGA pads. A via in a circuit board is used to join pads, polygons, and traces on various layers of the board. It is a core part of a PCB as it ensures proper connection in the board.
Vias offer connections between several layers of a PCB. Multilayer boards usually feature at least two layers of copper. Vias make it possible to fabricate a PCB with more than a layer of copper. There are different types of vias. Our main topic in this article is capped vias. Capped vias enable the design of via in pad due to their flat surface.
What is a Capped via?
A capped via is a type of via in which plating is included over the via hole. In such a case, the surface becomes metalized with cap plating thickness. Capped via technology is crucial for the fabrication of high density interconnect boards (HDI). This via features hole filling with resin. The design of capped vias helps in improving the density of the interconnection in PCBs.
The two primary technological solutions are resin via filling and copper via filling. The capped vias have hole filling with resin which helps in improving interconnections in HDI printed circuit boards. These vias integrate through holes’s space as SMD assembly points. The capped via technology comprises filling the holes after they have been plated. The copper thicknesses are usually >25µm. However, the copper thickness may be defined according to the customer’s specifications.
The resins integrated for “capped vias” feature some insulation properties. Also, the dimension of this resin varies according to changes in temperatures and as such, they are treated with heat for the consequent hardening. The resins are first planarized and a layer of copper covers them. The copper layer thickness is at least 15µm.
PCB manufacturers can apply this technique to realize various types of printed circuit boards. Also, these various applications is a reason for strong expansion.
Phases of filling holes in PCB
There are two distinct phases for filling the holes with resin. In the first phase, vacuum and variable pressure fill up the holes. This enables the proper filling of the holes without any risk of having space in the resin. The second phase requires cleaning the surface of the panel to get rid of any excess resin, and as such, improving its subsequent planarization.
Regardless of the final technology you selected, a mechanical brushing process referred to as planarization helps in removing the resin. Planarization is usually done after polymerization has been completed. Also, planarization uses some particular machines that integrate cup brushes.
The aim of planarization is to get rid of the excess resin and enable an even surface. This process is crucial for over-plating of the filled vias with copper in order to enable soldering of electronic components.
The “capped vias” technology is crucial in today’s PCB. This technology has helped in creating compliant circuit boards to market. Also, it has helped to meet some regulations standards, especially those associated with the growing HDI technology demand.
Why is Capped Via Technology Crucial in PCB Fabrication?
The rising demand for the miniaturization of printed circuit boards, particularly in some industries has, led to the design of complex PCB layouts. These layout process often involve embedding interconnecting holes into the Ball Grid Array (BGA) pads. Therefore, these same pad help to realize the internal circuitry of the printed circuit board and its typical SMT use. The benefit of this is evident in the reduction of the circuit board size. However, the limitation becomes evident in the complexity of the SMT mounting procedure. Also, there is the possible reliability lacks into printed circuit board assembly (PCBA).
A good amount of the epoxy glue can pass through the hole when there hole in a SMD pad. This can cause a void (dry joint) and as such, have a negative impact on the component or result in a sudden break of the connection of components in the board.
Two different approaches can be used to solve these kind of problems as earlier mentioned. Capped vias and filling copper are these two approaches. The filling copper technology involves the depositing extra copper in the hole, until you have been able to reach the requested filling percentage. There is always a dimple to avoid compromising the pad’s thickness. This is because the deposition of copper, even in minute amount, impacts the pad.
Capped Vias: A solution to complex PCB manufacturing
While some SMD components don’t need any planarity some components do. In such a case, the capped vias technology is last resort. This technology plays a significant role in the manufacturing of complex printed circuit boards. It involves filling the hole with a good amount of resin requires and then plating it. A thin copper cap is deposited into the pad. One of the benefits of capped vias technology advantage is how it preserves interconnections generated by the hole. Also, another benefit of this technology is the perfect planarity of the pad which enables easy mounting of each component.
There are other cases where the capped vias technology can be integrated. It can be integrated in buried vias rather than laser vias (BGA pads). Some micro-break at every corner can affect the buried vias plating when you apply the SBU technology. This occurs due to the mechanical processes the PCBs are exposed to
In this case, the risk is evident. This includes the unreliability of the PCBA and the malfunctioning of the interconnections caused by the buried via. Resin is used in filling up the buried vias in order to prevent this possible problem from occurring. In fact, this process makes the via robust and as well preserve the desired performance of the board.
Capped Vias for PCB Design
Everything keeps evolving. Things change and transformation is necessary in technology. With the constant evolvement and increasing advancement in technology, the PCB design and manufacturing processes keep getting better. As a result of this, industries need to keep up with this pace of innovations.
The printed circuit board industry isn’t an exception to this innovation. The PCB technology occupies a vast and dynamic space. The integration of vias in circuit boards have become popular because of the development of modern electronic devices and their applications. Vias are crucial for creating interconnection between PCB layers. These holes play a foundation role in ensuring interconnectivity between circuit board layers.
Also, this technique is useful in multi-plated and complex layouts. So, what are the benefits of capped vias in PCB design?
Enhanced thermal dissipation
Choosing the capped via technology for a PCB design helps to include extra capping to the manufacturing process. The efficiency of these vias worth the cost of a complex PCB design project. High power surface components usually feature thermal pads. Capped vias are a better option in this case compare to traditional routing styles.
Furthermore, the components of via offer support to heat management within the pads. The copper area become bigger when vias are dropped in from one side of the board.
Enhanced PCB density
Capped vias are ideal for use in high density interconnection boards. These vias enhance the density interconnection of complex boards. The circuitry requirements of a PCB layout will determine the suitability of capped vias. Capped vias technology is crucial for complex circuit boards.
Traditional circuit board routing techniques don’t offer support to the rising demand for PCB chips miniaturization. However, capped vias does. The vias’ position on the mount surface is a crucial factor to consider. However, this helps in preventing any issues for complex projects. Capped vias are a perfect option in PCB designs where space is crucial. As regards improving density and enhancing performance, capped vias are an ideal choice.
Improved performance capability
One of the benefits of integrating capped vias technology in PCB design is increased voltage capability. Vias feature resistance and inductance characteristics which in turn impact the flow of current. These variables can affect the functionality of a circuit board. Capped vias allow shorter paths and increase the performance of the board. Capped vias help to enhance the voltage of vias.
Vias Covering or Filling
Additional treatments are required on vias to increase their thermal performance. These treatments include capping, filling, covering, or plugging. Integrating any of these processes help to get rid of many assembly issues like short circuit or solder wicking. With a proper via treatment, it is possible to get rid of rework or troubleshooting.
Plugging prevents solder flow or wicking when soldering. Filling is a good option of via treatment. PCB fabricators use non-conductive epoxy to fill encroached paste. Some PCB fabricators make use of conductive paste to fill micro-vias to improve conductivity.
Conductive filling enables the transfer of signals form one part of the board to another. Therefore, this helps to improve the thermal properties.
Conclusion
Capped vias feature several benefits which include the reduction of EMI, improved routing density and enhanced thermal conductivity.
