Is Silicon Photonics Going to Kill Traditional Copper PCB Traces?

As data rates accelerate toward:

• 800G → 1.6T → beyond
• 224G PAM4 and future signaling
• ultra-high bandwidth interconnect

a new narrative is gaining traction: optical interconnect (Silicon Photonics) will replace electrical copper traces

At first glance, the argument seems compelling:

• optical signals have near-zero resistive loss
• no skin effect limitations
• immunity to electromagnetic interference
• extremely high bandwidth potential

However, the reality inside PCB Assembly, especially in HDI PCB and High-Speed PCB systems, is far more complex.

Because replacing copper is not just a matter of signal physics.

It is a matter of system architecture, manufacturability, cost, integration, and reliability

So the real engineering question is: Will silicon photonics eliminate copper traces—or simply redefine where copper is still necessary?

1. Why Copper Traces Are Reaching Their Physical Limits

Copper-based interconnects face fundamental challenges at high data rates:

• skin effect increases resistance
• dielectric loss increases with frequency
• signal attenuation rises sharply
• equalization becomes more complex

At:

• 112G PAM4
• 224G PAM4

the channel becomes: loss-limited

This drives:

• ultra-low-loss materials
• smoother copper surfaces
• shorter trace lengths

copper is not failing—but it is reaching its practical limits over distance

2. What Silicon Photonics Actually Solves (and What It Doesn't)

Silicon photonics enables:

• optical signal transmission
• extremely low loss over distance
• high bandwidth density

It solves:

• long-reach interconnect loss
• EMI/EMC issues
• bandwidth scaling challenges

But it does NOT solve:

• power delivery
• short-range interconnect complexity
• integration challenges at chip/package level

it addresses specific problems—not the entire system

3. Electrical vs Optical Interconnect: A System-Level Comparison

Electrical (Copper)

• strong for short distances
• supports power + signal
• simple integration
• mature manufacturing

Optical (Photonics)

• superior for long distances
• low loss
• high bandwidth
• requires conversion (electrical ↔ optical)

The key trade-off:

• electrical is simple but lossy
• optical is efficient but complex

4. The "Last Millimeter Problem": Why Copper Still Matters

Even in optical systems:

• signals originate electrically in chips
• must be converted to optical
• must be routed to optical interfaces

This creates: short electrical paths that cannot be eliminated

These include:

• die-to-package
• package-to-substrate
• substrate-to-PCB

This is known as: the "last millimeter problem"

Copper remains essential in this region.

5. Power Delivery: The Domain Where Photonics Cannot Replace Copper

Photonics can transmit data—but not power.

Every system still requires:

• voltage distribution
• current delivery
• ground reference

This is handled by: copper planes and traces

Even in fully optical systems: copper remains the backbone of power integrity

6. Integration Challenges: Packaging, Alignment, and Assembly

Optical systems introduce new challenges:

• precise alignment of optical components
• coupling efficiency (fiber ↔ chip)
• packaging complexity
• sensitivity to contamination

Compared to electrical interconnect:

• assembly is more complex
• tolerance is tighter
• yield is more sensitive

In advanced PCB Assembly, integrating photonics requires not just electrical expertise, but also optical alignment capability and process control.

ULTRONIU approaches such hybrid systems as a multi-domain integration problem—ensuring that high-speed electrical routing, packaging interfaces, and emerging optical interconnect requirements are aligned within manufacturable PCB and PCBA architectures.

7. Thermal and Reliability Constraints in Optical Systems

Photonics introduces:

• thermal sensitivity in optical devices
• wavelength drift with temperature
• reliability concerns in optical interfaces

Additionally:

• lasers and modulators generate heat
• packaging must manage thermal stability

thermal design becomes more complex—not simpler

8. Cost, Scalability, and Ecosystem Maturity

Copper PCB technology is:

• mature
• cost-effective
• scalable

Silicon photonics is:

• emerging
• expensive
• limited in manufacturing scale

Barriers include:

• equipment cost
• integration complexity
• supply chain maturity

large-scale replacement is not immediate

9. Hybrid Architectures: The Real Future of PCB Interconnect

The most realistic architecture is: hybrid electrical + optical systems

Where:

• optical handles long-distance, high-bandwidth links
• copper handles short-range interconnect and power

This creates:

• optimized system performance
• balanced cost and complexity

10. Strategic Conclusion: Replacement vs Redistribution

Silicon photonics will not eliminate copper.

Instead: it will change where copper is used

• long-distance → optical
• short-distance → electrical

Technical Summary（Engineering Conclusions）

• Copper traces face loss limitations at ultra-high speed
• Silicon photonics solves long-distance interconnect challenges
• Optical systems cannot replace power delivery
• Short-range interconnect still requires copper
• Integration and assembly complexity increase with photonics
• Thermal and reliability challenges remain
• Cost and ecosystem maturity limit rapid adoption
• Future systems will be hybrid

Silicon photonics will not kill copper—it will redefine its role in next-generation electronic systems.