Introduction

Printed circuit boards (PCBs) provide the foundation for building electronic circuits and products. With the ongoing miniaturization of electronics, PCBs have also become progressively smaller over the decades. This enables integrating more functionality into compact packages across a range of applications.

But how small can PCBs actually get? This article discusses the key factors that determine the smallest achievable PCB size based on available materials, fabrication technologies and assembly processes. Practical examples of tiny PCB implementations are also provided.

Drivers for Miniature PCBs

The main applications demanding miniature PCB sizes include:

• Wearable devices
• Internet of Things nodes
• Medical implants
• Microcontrollers and sensors
• Robotics and drones
• Mobile phones
• Microcameras

Smaller PCB footprints allow fitting into tight spaces, reducing overall product size and leaving room for additional components and features. Physics ultimately limits how tiny PCBs can get.

Limits of Conventional PCB Processes

Standard PCB fabrication using mature photolithographic techniques can routinely achieve:

• Line/space widths down to ~100μm with ~50μm vias
• Registration accuracy around 50-75μm
• Minimum hole sizes ~150μm with mechanical drilling
• ~6 mil (0.15mm) annular rings
• ~0.2mm edge clearance

These conventional PCB process limits restrict the smallest practically achievable board size to approximately:

5mm x 5mm boards

This allows a few hundred micron clearance on each edge along with routing space for connections between a few tiny surface mount components or connectors.

Advances in Fabrication Technology

Progress in fabrication techniques now enables much smaller PCB features:

Laser Drilling

Laser drilling can create extremely fine ~50μm holes for interconnections.

Photolithography

Improved lithographic printing processes allow narrow line/space down to 20μm.

Thin Core Dielectrics

Using flexible cores like polyimide with 12μm thickness reduces layer height.

Build Up Layers

Thin dielectrics like 15μm Ajinomoto with ~20μm lines/spaces enable dense multilayers.

Plating Technology

Electroless processing allows metal traces under 10μm.

Example of Miniature PCB

An example miniature PCB with dimensions of just 2mm x 2mm fabricated using the above advanced processes:<img src=”https://drive.google.com/uc?export=view&id=1zniTwNgwfM-zmSSM3VE05zjv14OC8J-N” alt=”Tiny 2mm PCB” style=”width:300px;height:300px;”>

Key implementation details:

• 4 layers with 2 build up layers
• Thin flexible 12μm polyimide dielectric
• 20μm line width and space
• Microvias with 50μm holes and 10μm laser drilling
• Gold traces and pads

This illustrates that with specialized fabrication processes, PCBs down to 2mm x 2mm size or smaller can be realized.

Current Practical Limitations

However, producing such tiny boards at scale still faces challenges:

• Smaller line widths increase copper roughness and DC resistance
• Tighter spacing leads to more leakage and interconnect issues
• Scaling standard solder mask and legend printing is difficult
• Thinner traces handle less current and are less reliable
• Registration and tolerance control is critical
• Plating ultra-fine traces uniformly is challenging
• Component assembly requires micro-scale precision

These factors make manufacturing limitations the primary barrier currently rather than fundamental PCB technology limits. As fabrication equipment, materials and skills mature, we may see increasingly smaller but production-ready PCBs.

01005 Discreet Passives

To assemble electronic circuits on miniaturized PCBs, the smallest possible discrete components must be used.

A key enabler is the 01005 package size for resistors and capacitors. With dimensions of just 0.4mm x 0.2mm, 01005 components allow extremely high component density.

The diminutive 01005 discretes are pushing the boundaries of PCB assembly using tweezers under microscopes. Their tiny size matches well with the capabilities of advanced HDI PCBs.

Chip Scale Packages

Besides the PCB itself shrinking, even smaller electronic packages are enabling further miniaturization:

Flip Chip CSP

With no peripheral leads, flip chip packages have footprints approaching the bare silicon die size. Pitch can reach below 100μm. This allows ultra-dense component mounting.

Wafer Level CSP

Here the packaging is implemented while the ICs are still in wafer form prior to dicing. This eliminates traditional packaging steps for a minimal footprint.

Both flip chip CSP and wafer level CSP integrate electronic function in exceptionally compact formats to complement smaller PCB sizes.

Emerging Technologies

Next generation technologies that could enable pushing PCB dimensions even smaller:

Additive Printed Electronics

Additive printing using techniques like inkjet can potentially deposit traces and components measured in microns. But material quality and precision remain challenges.

Embedded Actives

Concepts exist for embedding bare dies or active components within the PCB layers during lamination. This provides vertical space savings.

2.5D/3D Integration

Integrating multiple ultra-thin die or interposers in a package-on-package configuration allows packing more functionality vertically.

Flexible Hybrid Electronics

Combining thin, discrete ICs on a flexible substrate can provide a foldable, compact architecture.

So in the future, we may see diverse solutions for integrated systems that completely reimagine the conventional discrete PCB approach.

Current Record for Smallest PCB

Currently, the smallest commercially manufactured PCB seems to be just 1mm x 1mm in size, developed by a Japanese company.

It uses:

• 0.2mm thick flex substrate
• Traces and spaces down to 15μm
• Microvias with 0.02mm diameter
• Only two 0201 size SMD components along with two 0.04mm diameter wires

This shows that 1mm x 1mm is close to the practical limit achievable with existing processes. We may still see slightly smaller dimensions as

fabrication precision keeps improving.

Conclusion

There is a perpetual quest to make PCBs smaller to enable compact, portable electronics. Innovations in fabrication technology along with material advancements have pushed the boundaries on minimal PCB size down to 1mm x 1mm or below. But numerous manufacturing and assembly challenges remain in implementing such diminutive boards cost-effectively in commercial products. As process capabilities catch up with fundamental technology limits, we can expect increased utilization of miniature PCBs where space is at an absolute premium. Beyond just PCB shrinkage, 3D packaging techniques and emerging additive manufacturing processes could potentially revolutionize electronics manufacturing in the coming decades by providing alternatives to traditional PCB platform implementations.

FAQs

What are some key challenges faced when designing tiny PCBs?

High density routing, thermal management, component assembly, tolerance control, power delivery, mounting and testing are difficult with micro-scale PCBs. The fabrication and assembly precisions required are still developing.

How small can traces and spaces be made on a PCB?

Using advanced processes, trace widths down to 15-20 microns are possible. But thinner copper traces have higher resistance and lower reliability.research

What are some examples of products that use tiny PCBs today?

Hearing aids, medical implants, microcameras, sensors, watches, drones, jewelry electronics. Enabling applications where device miniaturization is critical.

How are components assembled onto extremely small PCBs?

Extremely precise pick-and-place equipment combined with skilled technicians and inspection under high magnification microscopes. Automated optical assembly struggles with such small scales.

Are there alternatives emerging to conventional PCBs for tiny circuits?

Yes, additive printing techniques can potentially deposit electronics directly onto substrates. 2.5D silicon interposers also allow vertical integration. Flexible hybrid electronics is an area with ongoing research.