HDI vs Standard Multilayer PCB: Complete Technical Comparison

The Question I Get Most Often

"Do I really need HDI, or is standard multilayer good enough?"

I hear this at least twice a week. Engineers see the price difference—HDI can cost 2-3x more than standard multilayer—and naturally wonder if it's worth the investment.

After 15 years of manufacturing both types, here's my honest answer: it depends on your component density and via requirements, not on how "advanced" you want to appear.

This guide will help you make that decision based on real technical and economic factors, not marketing hype.

Quick Comparison: HDI vs Standard Multilayer at a Glance

What Exactly Is HDI PCB?

HDI stands for High Density Interconnect. But what makes it "high density" isn't just smaller traces—it's fundamentally different via technology.

The Defining Feature: Microvias

Traditional multilayer PCBs use mechanically drilled through-holes. A typical drill bit is 0.2-0.3mm diameter. You physically can't go smaller without breaking drill bits constantly.

HDI boards use laser-drilled microvias—typically 0.075-0.15mm diameter. Lasers can create holes that mechanical drills simply cannot.

**Hommer's Definition**: If your board uses laser-drilled microvias, it's HDI. If all vias are mechanically drilled through-holes, it's standard multilayer. That's the real distinction.

HDI Via Types Explained

10 Key Differences: A Detailed Breakdown

Difference 1: Component Density

This is why HDI exists. Modern chips have ball pitches that standard PCBs simply cannot route.

Real example: An iPhone contains processors with 0.4mm ball pitch. You physically cannot route that with standard multilayer technology. HDI isn't optional—it's mandatory.

For our HDI PCB manufacturing capabilities, we routinely handle 0.5mm pitch BGAs with 0.1mm microvias.

Difference 2: Routing Capacity

Here's a calculation that changed how I think about PCB design.

Standard multilayer routing density: - 0.3mm via requires 0.6mm via pad - With 0.1mm trace/space, you get 1 trace between pads - Result: ~20 traces per cm

HDI routing density: - 0.1mm via requires 0.2mm via pad - With 0.05mm trace/space, you get 3-4 traces between pads - Result: ~60-80 traces per cm

**Hommer's Math**: HDI gives you roughly 3-4x the routing density of standard multilayer. That translates directly to smaller boards or fewer layers—both of which can offset the higher per-square-inch cost.

Difference 3: Signal Integrity

High-speed signals hate vias. Every via is a discontinuity that causes reflections and losses.

Why this matters: For signals above 3-5 GHz, via stubs in standard boards act like antennas, radiating energy and causing signal loss. HDI microvias eliminate this problem.

For high-speed applications, we combine HDI technology with proper RF material selection.

Difference 4: Layer Count Reduction

This is where HDI economics get interesting. Higher routing density often means fewer total layers.

Example: Complex digital board

See what happened? The HDI boards cost more per layer but need fewer layers. Total cost can be equivalent—and the HDI board is thinner and lighter.

**Hommer's Insight**: Don't compare apples to oranges. Compare the total cost of a finished, functional design. Sometimes HDI is actually cheaper when you factor in layer reduction.

Difference 5: Board Thickness

For wearables, mobile devices, and space-constrained applications, thickness matters.

HDI typically achieves the same connectivity in 40-60% of the thickness.

Difference 6: Reliability (Surprising Truth)

Many engineers assume thinner = less reliable. The reality is more nuanced.

HDI reliability advantages: - Shorter via paths = less thermal stress - Microvias = better plating quality (lower aspect ratio) - Less drilling = fewer potential defect sites - Cleaner signal paths = less electromagnetic interference

Standard multilayer reliability advantages: - More mature process, better understood failure modes - Larger features = more tolerant of handling damage - Simpler rework and repair - Longer track record in harsh environments

Difference 7: Manufacturing Complexity

Let me explain why HDI costs more by showing what happens in our factory.

Standard multilayer process: 1. Inner layer imaging → Lamination → Mechanical drilling → Plating → Outer imaging → Finish

HDI process (1+N+1): 1. Inner layers imaging → Lamination → Laser drilling → Plating → Additional lamination → More laser drilling → Plating → Outer imaging → Finish

Every "HDI layer" (the +1 in 1+N+1) adds a complete lamination and drilling cycle. More cycles = more cost, more time, more potential failure points.

Difference 8: Design Rule Constraints

Here are the practical design rules we use at our prototype service:

Standard Multilayer Design Rules:

HDI Design Rules:

**Hommer's Warning**: Not all HDI fabs have the same capability. Our "standard HDI" is another shop's "advanced." Always verify actual capability, don't assume.

Difference 9: Cost Breakdown

Let me give you real numbers from recent quotes:

Example: 100mm x 100mm board, 100 pieces

Cost drivers in order of impact: 1. Number of HDI layers (laser drilling cycles) 2. Number of lamination cycles 3. Minimum feature size (yield impact) 4. Via complexity (stacked vs staggered) 5. Material selection

Difference 10: When HDI Is Required (No Choice)

Sometimes HDI isn't a trade-off—it's mandatory:

Our turnkey assembly service handles both standard and HDI boards, allowing design optimization without changing vendors.

HDI Stackup Notation Explained

You'll see HDI boards described as "1+N+1" or "2+4+2". Here's what it means:

Visual representation:

`` 1+4+1 Structure: ┌─────────────┐ HDI Layer 1 (top microvia) │─────────────│ Standard Layer 2 │─────────────│ Standard Layer 3 │─────────────│ Standard Layer 4 │─────────────│ Standard Layer 5 └─────────────┘ HDI Layer 6 (bottom microvia) ``

**Hommer's Rule**: Start with 1+N+1. Only go to 2+N+2 if routing still won't fit. We've rarely needed 3+N+3 except for extremely complex designs.

Real-World Decision Framework

Here's the framework I use when helping customers decide:

Choose Standard Multilayer When:

• All components have 0.8mm pitch or larger
• Routing density is manageable with through-holes
• Cost is the primary driver
• Design is well understood/mature
• Lead time is critical (standard is faster)
• Application is industrial/harsh environment with conservative specs

Choose HDI When:

• Any component has 0.65mm pitch or finer
• Standard routing would require 10+ layers
• Board size is tightly constrained
• High-speed signals above 5 GHz
• Weight is critical (aerospace, wearables)
• Component count is very high

The Hybrid Approach

Often the best answer is selective HDI. Use HDI only where needed: - HDI under fine-pitch BGAs - Standard everywhere else - Often called "partial HDI" or "localized HDI"

This can reduce cost by 20-40% compared to full HDI while meeting all requirements.

Design Tips for HDI Success

Tip 1: Via-in-Pad for Fine-Pitch BGAs

For 0.5mm pitch and below, route microvias directly under BGA balls:

Via-in-pad requires filled and planarized vias—add this to your spec.

Tip 2: Stackup Planning

Work with your fab early. HDI stackups need careful planning:

• Layer assignment matters more than standard
• High-speed signals need reference planes
• Power delivery needs sufficient copper
• Thermal management requires thought

We offer free DFM review including HDI stackup consultation.

Tip 3: Test Point Strategy

HDI boards often lack space for traditional test points. Consider: - Flying probe instead of ICT - Boundary scan (JTAG) for digital ICs - Built-in self-test where possible - Functional testing at module level

Our testing services include flying probe for HDI boards.

Common HDI Design Mistakes

Mistake 1: Unnecessary HDI

The most expensive mistake: specifying HDI when standard would work. I've reviewed designs with 0.8mm pitch BGAs on HDI boards. Complete waste of money.

Mistake 2: Wrong Stackup Selection

Using 2+N+2 when 1+N+1 would suffice. Each additional HDI layer pair adds significant cost and lead time.

Mistake 3: Via Stacking Without Need

Stacked microvias are expensive and have reliability concerns. Use staggered vias unless you genuinely need the vertical routing density.

Mistake 4: Ignoring Aspect Ratio

Even microvias have limits. Trying to drill 0.1mm via through 0.2mm dielectric = 2:1 aspect ratio = marginal for microvia. Keep microvia aspect below 1:1 for reliability.

Mistake 5: Not Panelizing Correctly

HDI yields are lower than standard. Proper panelization with adequate board spacing helps. Work with your fab on panel design.

FAQ

Is HDI more reliable than standard multilayer?

It depends on the application. HDI microvias are actually very reliable (lower aspect ratio than through-holes). The complexity is in the multiple lamination cycles. For most applications, both technologies are adequately reliable when manufactured properly.

What's the minimum order for HDI prototypes?

We have no minimum order quantity for prototypes. Even a single HDI board is possible, though the setup costs make small quantities expensive per piece.

How much does HDI cost compared to standard?

Roughly 1.5x to 3x, depending on HDI complexity. A 1+N+1 board might be 1.5x a standard multilayer. A 3+N+3 with stacked vias might be 3x or more.

Can you convert my standard multilayer design to HDI?

Yes, but it usually requires layout modification. HDI enables different routing strategies that standard designs don't use. A direct conversion rarely captures the full benefit.

What's the lead time difference?

HDI typically adds 5-10 days to lead time due to additional processing cycles. Our standard multilayer prototype is 5-7 days; HDI prototype is 10-15 days.

Do you offer HDI with flexible materials?

Yes, rigid-flex HDI is possible but extremely complex and expensive. We recommend discussing requirements early. See our flex PCB capabilities.

Conclusion: Make the Right Choice

HDI and standard multilayer aren't competing technologies—they're tools for different jobs.

My recommendation: 1. Start with standard multilayer as your baseline 2. Move to HDI only when design requirements demand it 3. Use selective/partial HDI when full HDI is overkill 4. Work with your manufacturer early in design phase 5. Don't let marketing drive technical decisions

The best engineers I work with treat HDI as a tool, not a status symbol. They use it when it solves a real problem, not to impress colleagues.

Need help deciding? Contact us with your design files—we'll give you honest advice on whether HDI is necessary and what it will cost.

Related Reading

HDI technology intersects with material selection, testing, and assembly strategies. These guides provide context:

• **[PCB Materials Guide: FR4, Aluminum & Flex](/blog/pcb-materials-comparison)** – Material properties become more critical in HDI designs. Understand Tg, Dk, and CTE considerations.
• **[PCB Testing Methods Compared](/blog/pcb-testing-methods-comparison)** – HDI boards often require flying probe or X-ray inspection. Know your testing options.
• **[Turnkey vs Consignment PCBA](/blog/turnkey-vs-consignment-pcba)** – HDI boards with fine-pitch BGAs benefit from turnkey assembly where we control the entire process.

References

1. [IPC-2226](https://www.ipc.org/) - Sectional Design Standard for High Density Interconnect (HDI) Printed Boards
2. [IPC-6016](https://www.ipc.org/) - Qualification and Performance Specification for HDI
3. [Samtec HDI Design Guide](https://www.samtec.com/) - Via-in-pad and BGA escape guidance

*Written by Hommer Zhao, founder of PCB Portugal. We manufacture both standard multilayer and HDI PCBs, so I have no agenda in recommending one over the other—just whatever solves your actual problem. Last updated: December 2024.*