Stretchable PCBs Meet Structural Intelligence: The Rise of 'Stiff Islands'

From smart wearables to soft robotics and medical patches, modern electronics must do more than conduct signals - they must move, stretch, and survive real-life conditions. Traditional rigid PCBs simply can’t keep up. 

The answer lies in stretchable circuit boards (S-PCBs) - and more specifically, in a design concept called “stiff islands”: rigid sections embedded in a soft, elastic substrate that protect sensitive components while allowing flexibility around them. 

But fabricating such hybrid structures with precision? That’s the challenge where LPKF comes into the picture. 

What Are 'Stiff Islands' – and Why Do They Matter? 

Stretchable PCBs often face a core design challenge: they must flex and deform - yet many electronic components like ICs or connectors are inherently rigid. Simply embedding them in soft materials leads to failure under stress. 

That’s why researchers use “stiff islands”: small rigid zones strategically embedded within the stretchable substrate, acting as mechanical support platforms for delicate components. 

This hybrid design offers key benefits: 

• Mechanical decoupling: stress is absorbed by the soft areas, not the component 
• Improved fatigue resistance: devices withstand thousands of stretch cycles 
• Design freedom: allows rigid-flex integration in a soft, wearable form factor 

However, to make stiff islands work, the conductor geometry must be carefully routed across flexible and rigid areas—a job that requires laser precision. 

That’s where the LPKF ProtoLaser U4 comes in: it structures copper foils with exact isolation widths, no heat damage, and clean transitions, ensuring electrical and mechanical reliability across variable substrate zones. 

A Breakthrough from the University of Freiburg 

Researchers at the Freiburg Center for Interactive Materials and Bioinspired Technologies (livMatS) have developed an innovative, cost-effective method for producing S-PCBs using common materials like silicone and copper foil.  

Their process, published in Flexible and Printed Electronics (IOP Science) in 2024, uses laser structuring to define the copper tracks, which are then laminated into soft silicone substrates.  

Title: Stretchable printed circuit boards using a silicone substrate of variable stiffness 
Authors: Lorenz J. M. Letz, Jean-Pierre Bohn, Thomas Speck et al. 

This method balances durability and elasticity - critical for applications in wearables, soft robotics, and biomedical systems. 

The Role of LPKF: Precision Meets Flexibility 

A key step in the process is the selective laser structuring of copper foil for defining circuit paths. The team used the LPKF ProtoLaser U4 to precisely remove unneeded copper, leaving only the desired conductor geometry. 

Key contributions of the ProtoLaser: 

Structuring of fine copper tracks with ~60 µm isolation width 

Controlled ablation at varying power levels for different substrate conditions 

High speed with clean, burr-free separation of conductor areas 

Enables direct prototyping without masks or etching chemicals 

Why it matters: The durability and stretchability of the final S-PCB depend on exactly where the copper ends and silicone begins - and the laser defines that interface with surgical precision. This is especially critical in stiff island architectures, where rigid and soft regions must be cleanly separated but electrically connected. 

Empowering Next-Generation Wearables – With LPKF 

As applications demand smaller, more flexible, and more intelligent electronics, laser structuring is becoming a core tool in the design toolbox. LPKF enables research teams to:  

• Rapidly prototype custom geometries 
• Test mechanical behavior of circuit designs 
• Build and iterate in-house, without outsourcing delays 

From academic labs to startup incubators, LPKF is a trusted partner for stretchable, wearable, and bioinspired electronics.  

Get in Touch 

Whether you're prototyping flexible circuits or experimenting with stiff island PCB designs, LPKF gives you the tools to go from concept to reliable device - faster and in-house. Are you exploring stretchable electronics, soft robotics, or wearable devices? 

Let’s talk about how our prototyping systems can help bring your concepts to life: