Fresh PCB Concepts: HDI Microvia Features in Illustrations

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Often, when I work with a customer or a designer on an HDI board, I hear questions about the different types of microvias and even what exactly a microvia is. I thought this would be a good opportunity to explain microvias and discuss aspect ratios with microvias. This is important to know when designing an HDI PCB because the different types vary in complexity. And the more complex, the more this affects the cost.

According to the new definition within IPC-T-50M, a microvia is a blind structure with a maximum aspect ratio (which is a measure of the ratio between the depth of the hole and its width) of 1:1, terminating on a target land with a total depth of no more than 0.25 mm measured from the structure’s capture land foil to the target land.

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Figure 1: An illustration of a microvia.

In the case of microvia boards, we’re most likely to see the depth be the dielectric thickness or the distance between layers one and two. For example, when we consider our design guidelines, typically we see layer one to layer two dielectrics’ thickness or depth, being 60–80 microns.

NCAB_via_1_0621.jpg

The size of the microvia hole (its width) is within the 80–100 micron range. Considering these values, this provides an aspect ratio ranging from 0.6:1 to 1:1; keep in mind that as the dielectric thickness increases so must the size of the microvia.

Microvias are not just limited to the outer layers, or the dielectrics between layers one and two. We can see them within the inner layers and this ability to have more than one layer of microvia dictates the different types and its features as defined in IPC-2226.

Type I structures are those that contain a single microvia layer on either one or both sides of the core (Figure 2). It uses both plated microvia and PTH for interconnection so, in effect, it employs only blind via holes. They do not employ buried vias.

NCAB_via_2_0621.jpg

Type II structures are similar to Type I in that they contain just a single microvia layer on either one or both sides of the core and use both plated microvia and PTH for interconnection (Figure 3). Yet unlike Type I, these structures employ both blind and buried via holes.

NCAB_via_3_0621.jpg

Type III are a little more complex in that this structure or build contains at least two layers of microvia on either one or both sides of the core (Figure 4). It also uses both plated microvia and PTH for interconnection as well as both blind and buried vias.

The graphics we created are really the best visual to illustrate the various types of HDI features and the varying complexities. Many times when I get these questions I will send the illustrations rather than trying to explain the different features, or at least send the graphics first while I explain them. Of course, if you would like more details about the specific features (blind vias, buried vias, PTHs, etc.) I am more than happy to explain (or illustrate) that further, or perhaps on another column.

Ruben Contreras is a program manager and field application engineer at NCAB Group. 

 

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2021

Fresh PCB Concepts: HDI Microvia Features in Illustrations

06-17-2021

Ruben Contreras explains microvias and discusses aspect ratios with microvias. This is important to know when designing an HDI PCB because the different types vary in complexity. And the more complex, the more this affects the cost.

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04-14-2021

Every time a printed circuit board is exposed to soldering temperatures it is damaged. This is the case not only for lead-free soldering applications but also for eutectic soldering consisting of tin-lead.

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03-18-2021

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Fresh PCB Concepts: UL Certification for the Safety of PCBs

02-18-2021

Security is essential in the electronics industry. It is vital that users can rely on the finished products when considering factors such as fire and electrical safety, which means that both the PCB and the materials they contain must measure up to the highest standards. To ensure that the boards do conform, it has become common practice to UL certify the constituent materials or the PCB itself. In this column I am going to discuss UL certification, what’s involved and why you need it.

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Fresh PCB Concepts: RF PCB Designs–Challenges, Solutions and Tips

01-14-2021

Today, RF circuitry is crammed into a large variety of commercial products. Most of these are handheld wireless devices for medical, industrial, and communications applications. There are also applications in a variety of fields that are migrating from desktop models to become portable communications units.

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2020

Fresh PCB Concepts: How 5G is Influencing PCB Technology Trends

12-17-2020

We have all heard about the Internet of Things (IoT) and artificial intelligence (AI). In combination with the increased data transfer rates available through 5G, they can open up a whole new level of connectivity and communication between devices and things.

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11-05-2020

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Fresh PCB Concepts: 4 Characteristics to Consider When Selecting PCB Base Materials

10-08-2020

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Fresh PCB Concepts: Advantages of Application-Engineered PCBs

09-17-2020

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Fresh PCB Concepts: How Do You Calculate Finished Copper?

08-13-2020

How do you calculate finished copper on a PCB? This may sound simple, but Ruben Contreras has seen copper thickness called out either on the drawing or the specification, which can lead to additional EQs and, in some cases, additional costs. In this column, he explains the unintentional results that can come from misunderstanding what was requested.

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Fresh PCB Concepts: Pros and Cons of the 6 Most Common Surface Finishes

07-23-2020

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Fresh PCB Concepts: 7 Options for Via Treatment

06-18-2020

In some cases, it's acceptable to have via holes that are completely exposed in a PCB design. But there are many others where the hole should either be covered and/or tented, or in most cases, plugged. Jeffrey Beauchamp shares seven different via hole protection types based on IPC-4761.

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Fresh PCB Concepts: Why Design and Produce PCBs Beyond Industry Specification?

05-07-2020

While questions may be an annoyance, especially when you finally have a board designed and are ready to have it built for a product, Ruben Contreras explains the importance of asking these questions and requiring specifications.

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Fresh PCB Concepts: What You Should Know About Your Board’s Solder Mask

04-09-2020

It’s a weird time we’re all in, and for most designers, work has slowed down or even stopped. While work might have slowed, now is a good time to review some of your past PCB projects to see if you can improve functionality and reduce field failures. Harry Kennedy explains how one of the simplest ways to do that is to start from the top: solder mask.

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Fresh PCB Concepts: The Benefits of Being a PCB Producer Without Owning Any Factories

03-19-2020

With NCAB's infrastructure and factory management team based in China, many customers ask why they don’t own any factories. Jeffrey Beauchamp explains how it's part of the company's long-term strategy and an advantage to our customers that they don’t own any factories. Instead, they “own” what is most important: the relationship with the factory.

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2019

Fresh PCB Concepts: Designing a PCB for Telecom Applications

12-12-2019

Jeff Beauchamp and Harry Kennedy discuss PCBs for telecommunication applications, including key factors to consider, such as design and material considerations. They also recommend involving your PCB supplier at the time of design to help ensure manufacturability at the lowest possible cost.

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Fresh PCB Concepts: The Current Material Situation

11-11-2019

We have all heard about the component crisis in the circuit board industry, and maybe you heard about the CCL shortage, but how many are aware of the bare board material shortage? Ruben Contreras explains the current material situation and tips to address this issue.

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10-23-2019

When faced with critical time-to-market situations, it is all too easy to say, “It doesn’t matter because this is just the prototype; we can fix this later.” However, if the design is perfected from the beginning, cost savings can be applied, and manufacturability can be ensured. Perhaps most importantly, the design can be adapted with reliability in mind, leaving a seamless transition from prototype to production. How do we get it right from the start?

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Fresh PCB Concepts: Why Material Selection Matters

10-02-2019

When you’re designing a PCB, it’s standard to call out FR-4 material, but you could be holding yourself back or even exposing your board to risk by not knowing more about PCB materials. Let’s take a small look into why. What Is FR-4, exactly? Harry Kennedy of NCAB explains.

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Fresh PCB Concepts: Qualities of Medically Applied PCBs

08-26-2019

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