Microvias and Their Aspect Ratios

If you’re designing a modern PCB that needs microvias, the aspect ratio of these interconnects is important. A wide range of fabrication capabilities are required to manufacture the different sizes, shapes, and aspects of these vias. Aspect ratios of vias are also important for plated through-hole (PTH) and buried via (BVID) performance, as well as reliability. The way you manage these aspect ratios will impact the quality of your end product.

microvia aspect ratio are determined by the diameter of the finished hole and the thickness of the board material. A high aspect ratio can result in damage to the plated copper network within the hole, while a low aspect ratio increases the consistency of the plating process. The aspect ratio of a via also affects the plating time and can increase the likelihood of thermal stresses that may cause the via to crack.

In the PCB manufacturing process, vias are formed by drilling holes into the surface of a printed circuit board. This can be done mechanically or by using a laser. A laser drill is a more precise method that allows the fabricator to achieve lower aspect ratios than can be achieved by mechanical methods. However, a laser drill can only drill to a certain depth, which restricts the size of the final via. This is why it’s important to consider the aspect ratio of your PCB design as you select your fabricator.

Thin Microvias and Their Aspect Ratios

When determining the dimensions of your microvias, you must take into account the diameter of the finished hole and the thickness to which you can drill, as well as the size of the annular rings that surround the drilled holes. Ideally, you want to use a smaller diameter than the finished hole for the annular rings. This will minimize the amount of metal needed for these rings and increase the strength of the via, making it able to withstand the stress of soldering.

The aspect ratio of your buried or blind microvias can also be affected by the thickness of the core and dielectric layers, as well as the copper weight. In general, a higher aspect ratio will be easier to fabricate with a thinner dielectric layer and higher copper weight. This is because a thin dielectric can bow during the drilling process, leading to mis-registration and microvia spacing problems. A thicker dielectric can make it harder to drill a large enough hole for the desired aspect ratio and will also limit the plating thickness.

Another factor to consider when selecting the aspect ratio of your buried or blind microvias is how they will be filled. For instance, if the buried or blind vias will be completely filled with solder, you must choose an aspect ratio that allows the solder to flow into the via’s barrel and fill it. If you do not, the solder may wick down the sides of the via and weaken the connection with the component’s pad.

With the right engineering and manufacturing partners, you can easily meet your microvia aspect ratio requirements. Hemeixin PCB has the expertise to work with your designer to make sure that the traces you need are placed in areas that can accommodate the desired aspect ratios.

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