Is HDI PCB Worth It for Mid-Volume Projects?

Is HDI really worth it? That is the question over which many project teams will ponder. Our times have seen HDI technology finds its way into everything, from smartphones to automotive controllers to many a critical application. The advantages are clear: HDI allows for smaller, lighter and more complex devices, while certainly being more expensive and not to mention with its own share of challenges. But the question remains: for a mid-volume project, where is this break-even point where a conventional multilayer PCB will have its disadvantages outweigh its advantages, and where the transition to HDI will no longer be the question of a simple upgrade, but the correct solution for a given application? This will be the question that we will be trying to answer in the article for today.

Conventional and HDI PCBs?

The distinction comes down, at the most fundamental level, to how densely a board can be packed with traces and components. Conventional multilayer PCBs typically rely on through-hole vias, with trace width and spacing in the range of 75 to 100 micrometers. These have been the backbone of the electronics industry for decades and their manufacturing processes are well-established and supported by fabricators worldwide.

HDI, by contrast, works with much finer lines, closer spacing, and advanced via structures such as microvias and stacked, blind and buried vias. Laser drilling replaces mechanical drilling for the smallest holes, and sequential lamination allows for layer stacks of more elaborate design. You get a dramatic increase in wiring density, estimated by some to be up to be a 40% higher component density compared to standard multilayer boards.

There are other implications as well. HDI PCBs can accommodate fine-pitch components such as modern BGAs and chip-scale packages, and they make possible designs of both smaller sizes and greater functionality. But these advantages are balanced by HDI’s higher cost, and not to mention a particular set of challenges specific to HDI.

Cost Structures of HDI PCB

The price gap between HDI and conventional PCBs is significant, especially for small-volume runs, the main cost drivers being the use of laser-drilled microvias, additional lamination cycles, and tighter tolerances throughout the stack-up and imaging processes. Even when labor costs are low, a design executed in HDI will demand a price premium two to three times higher than the same design executed in a conventional multilayer PCB.

Another advantage for standard multilayer PCBs is the decades of process optimization, commodity pricing for materials, and broad supplier competition. Setup and tooling costs are lower, and the economies of scale start at very modest production volumes.

For mid-volume projects, say, between 2,000 and 10,000 units. The calculus is more nuanced. High volumes can absorb the fixed costs of an HDI project like NRE, tooling and process engineering. But for a mid-volume product, these costs will not disappear entirely in the unit price. If the NRE is $5,000 for HDI and $2,000 for standard multilayer, the per-unit cost difference for a run of 5,000 boards is going to be $0.60 for HDI, before considering the higher ongoing fabrication costs per board.

This premium, however, will narrow for dense designs. A 10-layer standard PCB that pushes the limits of traditional through-hole technology will require additional layers, board real estate, or complex via fill operations. In such cases, the difference between HDI and non-HDI narrows, since advanced features are going to be necessary regardless of the stack-up.

When Is HDI PCB Justified?

HDI PCB is not the prerogative of high-end smartphones. The technology is justified wherever product requirements demand a level of density, miniaturization, and performance that cannot be offered by traditional multilayer PCBs. The clearest cases are in applications where board size and thickness are crucial: advanced wearables, implantable medical devices, and compact industrial modules. BGAs with less than 0.65 mm pitch and other fine pitched components, cannot be routed on standard multilayer PCBs without resorting to extremely complex and expensive workarounds.

You will also want to consider the demands on the performance of your product. HDI boards offer shorter trace lengths and better control of impedance, things that are crucial for high-speed signals, radio-frequency applications, or mixed-signal layouts where crosstalk and electromagnetic interference are issues. A 2023 survey reported 70% of engineers citing “signal integrity” as a key reason for adopting HDI, many of whom working on projects of compact IoT and automotive designs.

There are also situations for which HDI is the only possible solution. A medical device requiring multiple sensors, Bluetooth, and battery management in a package the size of a coin cell would be impossible to realize with through-hole vias and standard trace widths. In a similar scenario, the higher price is well worth it to be able to launch a product that meets the form and function conceived for your product.

When to stick with Standard Multilayer PCB?

But standard multilayer PCBs remain the workhorses of the industry for good reason. They offer reliable performance, lower cost, shorter lead times, and a vast ecosystem of fabricators worldwide. For an application where space is not going to be a stringent requirement, conventional PCBs offer lower risk and better value. The examples for this are industrial controllers, desktop electronics, and large-format sensors.

Another advantage for conventional PCBs is their repairability and supply chain flexibility. Standard boards are easier to rework and modify. This quality shines when unforeseen changes arise during validation or after deployment. Despite the worldwide growth of HDI, not every fabricator will be able to handle fine lines and microvias with the same yields as the major players, meaning that standard PCBs offer more sourcing options and less supply risk.

A common pitfall is what is called overspecification, when you load up HDI features on a product that does not truly require them. This will lead to unnecessary engineering complexity, higher costs, and longer manufacturing times without real benefit to the product or its user.

Additional Considerations

Mid-volume projects are the ones too large for prototyping-oriented “quick-turn” PCB shops, but not big enough to leverage the absolute lowest per-unit costs from large-scale, offshore production lines. In this difficult middle position, the impact of non-recurring engineering costs is less important, and additional complexity in the design must be justified against its lifetime value.

Design for manufacturability, because small design choices such as the number of HDI layers, the type of microvias, or the stack-up configuration will make a difference of weeks in lead time and dollars per unit. You will want to consider hybrid approaches like using HDI only in certain regions of the board or for specific layers. You may find that these middle ways balance performance needs with cost.

Supply chain factors also come into play: fabricator capability, lead time, and logistics. It is not a bad idea, and especially if you are just making this transition from conventional PCB to HDI, to consult multiple board houses early in the design process to validate both feasibility and cost.

Conclusion

The question of transitioning from a conventional PCB format to HDI PCB is a difficult one, especially for a project of mid-volume for which the premium in price can very well outweigh the advanced features promised by HDI: higher density, miniaturization, and advanced performance. But if your product absolutely demands a compact form factor, fine-pitched components and high-speed signaling, HDI is well worth the cost. If you yourself are in the process of deliberating this difficult dilemma, we hope that this article was able to help you and shine some light on the possible implications of either of these choices. We hope you enjoyed reading and look forward to seeing you next time.