Published On: Fri, Mar 23rd, 2018

The Connection of Aspect Ratio with Multi-Layered PCBs

Have you ever tried making a pot over the potter’s wheel? Ok! You haven’t tried! But you must have seen a pot maker, either in video or in reality, designing the pot over his wheel. You will, definitely, agree with my statement that it is really difficult to set those curves right for the pot but it is extremely important to set them right in order to get a stable, smooth and long-lasting pot.

Similar is the case with designing and manufacturing a Multi-Layered PCBs. Aspect Ratio is a significantly important factor in the entire process of building the multi-layered PCB or printed circuit board.  But before jumping onto Aspect Ratio, let us first learn about vias and annular rings.

What are Vias?

Vias are the holes that are drilled through traces of PCB Layers so as to connect the trace present on one layer to the other. Vias are of 3 types:

Blind Vias: Drilled for the purpose of establishing a connection between the outer layer of the PCB to an internal layer, but not more than that.

Buried Vias: These are drilled for the purpose of establishing a connection between two or more internal layers of the PCB.

Through-hole Vias: These are drilled through the total PCB altogether in an attempt to join the first and the last layer of the PCB.

Now, annular rings, made up of copper are placed around these holes so as to provide ourselves a connecting surface for placing components. If not placing any component, annular rings are just used for decoration purposes so as to give us a nice clean looking via.

What are Aspect Ratios?

Aspect Ratio, in the field of printed circuit boards, is defined as the ratio between the thickness of the board and the diameter of the vias drilled by you.

As an example, please suppose that you have a printed circuit board with you with a thickness of 0.3” and you drilled vias having a diameter of 0.03” on it. So, what will be the Aspect Ratio? Yes! Correct! It will be 10:1.

The significance of Aspect Ratio in PCB Manufacturing Process

Taking above given example into consideration, as the aspect ratio of 10:1 starts increasing, more plating will be needed to surround the via as compared to the portion of which is drilled. This will impact the quality of your printed circuit board as more the aspect ratio; more the manufactured printed circuit board is at the risk of cracking while soldering due to z-axis expansion.

Hence, lower the aspect ratio, more strength the manufactured printed circuit board will have. Boards with low aspect ratios will make way for constant and consistent plating throughout the via.

So, while designing a PCB, one must keep in mind two things for achieving a low aspect ratio. Keeping the board thickness to the minimum and the drill diameter must be as small as possible. This will help you achieve a PCB which will stay strong throughout its lifetime.

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