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What Are High-Density Interconnect (HDI) PCBs?
High-density interconnect PCBs are advanced circuit boards that enable the integration of more components and connections within a small space.
They achieve this by using finer lines and spaces, smaller vias, and higher connection pad densities compared to standard PCBs.
PCB manufacturers can achieve miniaturization through several techniques. For example, using microvias allows components and traces to be densely packed.
Thinner lines and closer conductive path spacing improve routing density.
Meanwhile, using thinner dielectric materials allows for a higher layer count while leading to a thinner board.
Also, blind vias and buried vias make the vertical interconnects more efficient while saving outer layer space.
Here are the main characteristics that set a high-density interconnect PCB apart from a standard PCB:
- Layer count: Manufacturers produce HDI PCBs with multiple layers, usually between 4 and 20, depending on the intended application and circuit design. If the PCB has 30+ layers, it’s more suitable for advanced applications.
- Line width: Line width is the conductive path width. Typical HDI circuits have a line width between 0.05mm (50um) and 0.15mm (150um). This line width can be smaller or higher based on the circuit specifications and production process.
- Line spacing: Spacing, on the other hand, is the distance from one conductive path to the next. It has similar measurements as the line width—0.05 mm to 0.15mm. Adequate spacing reduces the risk of short circuits.
What Are Standard PCBs?
Printed circuit board.
Standard PCBs are flat boards that mechanically support and provide connections for electronic components. Manufacturers fabricate these circuit boards with one or more layers, each with a substrate and conductive traces.
The substrate is typically a fiberglass (FR-4) material with excellent durability and insulation. Copper is etched on the substrate, forming conductive traces that enable electrical signals to flow between components.
Standard printed circuit boards are cost-effective because they’re fabricated in bulk, lowering costs per unit.
A simple design process, which only requires standard components, reduces overall costs.
The manufacturing processes are well-refined, resulting in better performance and higher yields. Standard PCBs also undergo quality control to meet high-quality standards.
Head-to-Head: A Comparison of HDI and Standard PCBs
There are several key differences between HDI PCBs and standard PCBs. Let’s look at some of the most important:
| Category | High-density interconnect | Standard |
| Line width and spacing | 0.05mm to 0.15mm | 0.10mm to 0.25mm |
| Layer count | 4 to 32 or more layers | 1 to 4 layers |
| Material composition | High-performance materials, such as Teflon, FR-4, polyimide, etc. | FR-4 |
| Manufacturing complexity | More complex processes. HDI PCB relies on techniques like microvias and laser drilling. | Simpler manufacturing processes. It uses automated drilling, chemical etching, electroplating, and other techniques. |
| Cost considerations | More expensive. It uses high-performance materials and advanced processes. | Less expensive due to simple materials, processes, and design. |
Advantages of HDI PCBs
HDI PCBs are beneficial for consumers and various industries. They ensure better device quality, reliability, and performance to meet required standards. Let’s have a deeper look.
Increased functionality in a smaller footprint
A greater number of components can be integrated closely together onto HDI boards. As a result, electronic devices gain more functionality without increasing in size.
Blind vias, microvias, and buried vias make this possible due to their efficient routing.
Improved signal integrity and performance
HDI-printed circuit boards have shorter signal paths, which result in faster transmission without signal loss. Because of this, signal integrity and performance significantly improve.
Layers are more compact, with stack-ups and short interconnects decreasing electromagnetic interference (EMI), like crosstalk, switching noise, and reflections.
HDI technology also often uses advanced thermal management techniques, which further boost performance stability.
These ensure that components operate in their specified temperature range, reducing the risk of sustaining damage and enhancing reliability.
Potential for weight reduction in devices
HDI PCBs are made from strong, lightweight materials like polyimide, Teflon (PTFE), and FR-4, resulting in lighter devices. They also benefit from layer optimization and microvias, which increase component density to reduce weight on smaller boards.
Disadvantages of HDI PCBs
Compared with standard printed circuit boards, HDI PCBs have drawbacks that can impact costs and production. It’s important to be aware of them to ensure this circuit type meets your needs. Here are a few worth mentioning,
Higher cost due to complex manufacturing processes
Manufacturing HDI PCBs is more expensive than conventional printed circuit boards.
The process requires laser drilling machines to create microvias and lamination presses for lamination cycles.
Manufacturers use highly efficient and costly substrates during fabrication. Substrates ensure that HDI PCBs have excellent electrical and thermal management properties, which is essential for small devices.
However, these materials can affect the cost-effectiveness of an HDI board, especially if you’re looking for low-priced products.
Potential design challenges for high-density routing
The very feature that elevates the efficacy of HDI PCBs—high-density routing—can also become a disadvantage.
If the HDI PCB design is less than optimal, there can be increased risks of signal integrity issues such as crosstalk and signal loss.
This is because the routing becomes denser, and the spacing between traces gets tighter.
Another design issue is heat dissipation.
If not addressed correctly, densely connected components on the circuit board can increase heat production, which can impact the devices’ reliability and performance.
Lower yield rates during fabrication
The advanced manufacturing techniques required for an HDI PCB, such as microvias, laser drilling, and precise layer alignment, are more complex and demanding than those used for a standard printed circuit board.
This complexity increases the likelihood of defects during fabrication, such as misaligned layers, incomplete vias, or electrical shorts.
As a result, a higher percentage of boards may need to be discarded or reworked, driving up production costs and time.
Design Considerations for HDI PCBs
HDI PCBs Design Considerations
Consider the following factors when designing your circuit board. Adhering to them will keep you on the right track for a successful manufacturing process.
Line impedance control for high-speed signals
High-speed signals require uniform impedance to ensure proper transmission. This is achieved through carefully designing the trace width and spacing. Any variations can lead to signal reflections, which degrade signal quality.
PCB stack-up and dielectric materials also play a part in reaching the desired impedance. So, you must factor these into your design and configure components to match your required impedance output.
Via Management Strategies (Blind Vias, Buried Vias)
Buried vias and blind vias provide a higher routing density while preserving signal integrity. Using these vias ensures efficient usage of the inner layers.
Consider adding via in-pads to reduce signal paths and conserve board space. Also, shortening via stubs decreases signal degradation and reflections.
Material Selection for High-Density Routing
HDI circuits consist of laminate materials that provide high-density routing. Those laminates should feature a lower dielectric loss factor and permittivity, which maintains signal integrity.
Consider choosing polyimide, PTFE, and modified FR-4 as the substrate material. Importantly, the selected material must tolerate the micro via drilling process.
Real-World Applications of HDI PCBs
Real-World Applications of HDI PCBs
HDI PCBs boost performance in everyday electronics found across all industries. Some examples include.
High-Performance Computing Systems and Servers
The higher component density in HDI PCBs gives smaller computing systems increased processing power.
Data center servers, for example, benefit from these PCBs, which provide rack-mounted equipment with more computational power.
This enhancement improves energy efficiency and performance.
High-density interconnect PCBs also enhance signal integrity, boosting server data speeds.
Advanced Mobile Devices and Wearable Electronics
Tablets, smartphones, and wearables use HDI technology, which provides them with a small form factor and advanced capabilities.
Miniature, lightweight, and thin devices like smartphones typically feature sensors, powerful processors, and high-resolution cameras.
HDI PCBs’ high component density and compactness make that integration possible.
HDI PCBs also enable advanced technology to fit inside the small space of wearables.
Medical Devices Requiring Miniaturization and High Functionality
Medical wearables like heart rate, blood pressure, and glucose monitors require a small PCB with built-in functions.
HDI PCBs allow sensors, Bluetooth modules, Wi-Fi modules, GPS, NFC, and other components to integrate into a compact space.
This results in lightweight, low-power, miniaturized medical devices with high performance for constant health monitoring.
Additionally, HDI PCBs are practical for cochlear implants, neurostimulators, and pacemakers. Other applications include hearing aids, handheld diagnostic devices, and endoscopic devices.
Choosing the Right PCB for Your Project
Choosing the Right PCB for Your Project
Standard PCBs and HDI PCBs offer different functionalities for the intended application. When choosing between the two types of PCBs, consider the following points to simplify your decision.
Consider project requirements
The project specifications can give you a better idea of what to select.
Size
HDI PCBs are ideal when the project demands a small form factor. With this technology, the components can fit in a tight space on the PCB, leading to portable devices.
Standard PCBs are suitable if the project isn’t size-strict. There’s more room for the components and PCB.
Performance
HDI PCBs may be a better option for projects requiring a high level of performance. Their short signal routes make them ideal for this purpose.
Nonetheless, standard PCBs work for applications that don’t need high electrical performance.
Evaluate budget limitations
HDI PCBs have a higher fabrication cost because of the advanced materials and processes. On the other hand, standard PCBs (simple designs) are more cost-effective for those on a budget.
Seek expert advice from a qualified PCB manufacturer
Ask a qualified PCB manufacturer for guidance on your project needs. They will discuss manufacturing processes, feasibility, and budget considerations to achieve the best result.
PCB manufacturers also advise whether an HDI or standard design will work best for your requirements.
We Can Help You Achieve High-Density Success
WellPCB handles complex HDI projects that meet IPC Standards for HDI PCBs. We use advanced manufacturing processes, including micro via drilling, precise line spacing and width, and lamination.
We perform thorough testing and inspections to meet the highest quality standards and ensure reliability.
By doing so, it also guarantees a high-performance PCB that meets your needs.
Are you ready to work with us? Get a quote for your next HDI PCB project today.
