What Is Considered a Microvia?
When designing your PCB, one of the most important things you should do is keep the size of your circuit board as small as possible. This needs to be done for the total size of the product and its components to be held at a minimum, thus ensuring that your product is as compact and lightweight as possible. However, if you use printed circuit board (PCB) technology, some elements are used to connect the copper planes on a PCB, such as microvias.
A microvia is considered to be the smallest hole that can be created through a printed circuit board. It is usually used for various functions such as making connections or soldering on components. This post covers the different types of microvias, their advantages, and some things to consider when using them.
What Are Microvias?
A microvia is a small via that can be used in surface-mount technology (SMT) boards. Microvias are similar to vias, which are holes that connect two different layers or planes of a board. However, unlike vias, microvias are smaller and have less depth than standard vias. Depending on your specific application, they are also available in various shapes and sizes.
Microvias can be used for many different purposes, including:
- Connecting two other planes to form a circuit path;
- Creating a signal path between two adjacent layers;
- Creating pathways for power supply connections; and
- Creating pathways for ground connections
Why Should You Use Microvias over Vias?
There are several reasons why a designer might choose to use microvias instead of larger ones:
Reduced Cost
The cost per hole is less for smaller holes than for larger ones. This may be important if you are designing a board with large numbers of holes or if you are trying to save money on your design costs.
Reduced Thermal Expansion
The thermal expansion coefficient (TEC) for microvia holes is lower than that for standard through-holes because their diameters are typically much smaller than their depth. A smaller TEC means less strain on the circuit board when it is heated up and cooled down regularly during its lifetime.
Improved Reliability
Because microvias have such small diameters, it is difficult for them to become clogged with solder during assembly - especially when using surface-mount components that require reflowing to be soldered successfully.
Better Routing Performance
Microvias can be routed directly underneath other components without worrying about routing around them, which can help simplify the routing process and improve performance.
Improved Signal Integrity
The impedance of a via decreases as its diameter decreases, so vias with smaller diameters have better signal integrity than those with larger diameters.
Increased Resistance to Corrosion
Larger holes have a greater surface area exposed to environmental conditions such as moisture, dust, and dirt, which can accelerate corrosion of copper traces leading to shorts between adjacent traces or even complete failure of the trace itself over time. Microvias expose less copper to these corrosive conditions, thereby increasing the longevity of your circuit boards.
Common Microvia Types
Microvias come in various types. Some of the common ones include:
Through Microvias
These are holes that go all the way through a board’s layers. They allow through-hole components to be soldered onto the board’s surface or bottom layer. Through microvias are typically found on double-sided boards, which do not have any plated through holes because there is no need for them in this case.
Blind Microvias
These are similar to through microvias, except that they do not go all the way through a board’s layers. Blind microvias can be placed anywhere on a PCB without causing problems or requiring special attention from designers or manufacturers during production or assembly processes. In fact, blind microvia placement does not affect how your product looks after it has been assembled at all.
Stacked Microvias
Stacked vias are two or more blind vias placed close together vertically such that one is above another and connected by an electrical trace or copper path beneath them both. This configuration allows you to add extra connections between two layers without increasing the plated holes required on your PCB.
Staggered Microvias
Staggered microvias are small holes that are drilled into the board, with the ends staggered on opposite sides of the board. This allows for the easier placement of components, especially in high-density applications.
Microvia Design Considerations
The design of a PCB with microvias differs from that of a PCB without microvias. There are several essential considerations that must be taken into account when designing microvias. These considerations include:
Microvia Density
The number of vias you need to create depends on the density of your board and the size of your traces. The more densely you place things on your board, the more vias you need to connect everything.
Microvia Spacing
How close together your microvias should be placed depends on what they connect, what they are made of, and their size, which is the diameter. You will want to keep your spacing as tight as possible, so there is no concern about signal integrity or mechanical strength issues caused by excessive bending around corners.
Microvia Placement
You will want to place your vias in areas where they will not interfere with other components such as heat sinks or capacitors so that when these components are placed onto your board, they do not cover up any of your vias and cause problems during manufacturing or in-use operation of your product.
Final Word
Knowing how to interpret microvias is crucial as they can significantly affect the electrical performance of a PCB. If you are new to using these small copper holes, we hope this guide has given you some insight into microvias and why they are essential to board design. If you want to learn about microvias in HDI PCB, check out HemeixinPCB. Hemeixin is a leading PCB manufacturer and can help you pave your way to fabricating a successful PCB with microvias in it.
