Glass Interposers for High-Frequency Circuits

In high-frequency electronics, every fraction of a decibel counts. Engineers designing for 5G, radar, and high-speed computing are constantly battling signal loss, interference, and thermal issues. Traditionally, silicon and organic interposers have been the go-to choices for chip packaging and signal routing. But now, glass interposers are emerging as the superior alternative.

Less interference. More performance.

With better dielectric properties, lower signal loss, and superior thermal expansion matching, glass interposers are setting a new standard:

• Better dielectric properties: This means glass doesn’t absorb and distort signals like silicon does. Signals move faster and with more clarity.

• Lower signal loss: Less resistance means more of the signal reaches its destination. In contrast, silicon absorbs energy, weakening the signal.

• Superior thermal expansion matching: Glass expands and contracts at nearly the same rate as silicon chips and PCBs, reducing stress and preventing cracks over time.

  
  

Think of it like this: If silicon interposers are like running on a rough dirt path, glass interposers are like running on a smooth highway. The signal moves faster, with fewer obstacles.

By improving these three factors, glass interposers are transforming RF design, making devices more efficient, powerful, and reliable.

An interposer is a thin layer placed between microchips to connect them and improve performance. Think of it as a high-tech bridge that makes communication between electronic parts faster and more efficient.

There are three main types:

1. Organic Interposers – Made from PCB-like materials, good for low-cost applications but not ideal for high frequencies.

2. Silicon Interposers – Better for high-performance computing but causes higher signal loss at RF frequencies.

3. Glass Interposers – A breakthrough technology offering low signal loss, high reliability, and better overall performance.

   
   

How Glass Interposers Reduce Signal Loss

1. Glass Lets Signals Flow with Minimal Interference

Glass has superior dielectric properties, meaning it doesn’t interfere with signals as much as silicon does.

• Dielectric constant (Dk): Lower values mean signals travel faster and with less distortion. Glass has a Dk of ~4-5, while silicon is much higher at 11.7.

• Loss tangent (Df): This measures how much signal is lost as heat. Glass has a low Df of 0.0004-0.002, whereas silicon is 0.01-0.02.

Glass interposers allow signals to move faster and cleaner, like cars on a freeway compared to stop-and-go traffic.

2. Glass Reduces Signal Weakening (Attenuation)

Every material absorbs some part of an electronic signal. The less it absorbs, the better the signal quality.

• Glass has high resistivity (10¹² - 10¹⁶ ohm-cm), meaning it doesn’t absorb much signal energy.

• Silicon has much lower resistivity (1 - 100 ohm-cm), meaning it absorbs more and weakens signals.

Glass keeps signals strong and clear, while silicon weakens them over long distances.

3. Through-Glass Vias (TGVs) Make Vertical Connections Better

Through-Glass Vias (TGVs) are tiny conductive holes that allow electrical signals to pass through different layers of a circuit.

• TGVs reduce extra noise and interference that happens when signals have to travel sideways through longer paths.

• Compared to silicon’s Through-Silicon Vias (TSVs), TGVs have lower capacitance, leading to less distortion and better performance at high frequencies.

  TGVs in glass interposers allow cleaner, faster, and more direct signal paths, improving circuit efficiency.

Manufacturing Challenges and Advancements

While glass interposers offer significant advantages, their adoption has been limited due to certain manufacturing challenges:

1. Processing Complexity

Creating glass interposers requires precision fabrication techniques, including:

• Laser drilling or wet etching to create TGVs.

• Plasma-enhanced chemical vapor deposition (PECVD) for dielectric coatings.

• Advanced metallization processes for conductivity.

Recent advancements, including higher precision laser drilling and improved metallization techniques, have significantly reduced these challenges, making glass interposers more viable for mass production.

2. Cost Considerations

• Historically, glass processing was more expensive than silicon, but improvements in yield and scalability have brought costs down.

• Companies are now investing in panel-level manufacturing, enabling large-scale production at lower costs.

  
  

Glass Interposers in Action

1. 5G Antennas: Glass interposers for 5G mmWave modules to reduce power consumption and improve signal efficiency.

2. Aerospace Radar Systems: Glass interposers to improve precision radar performance, enabling longer-range detection and lower signal interference.

3. AI & High-Performance Computing: Glass interposers to support high-density chiplet integration, improving processing speed and heat dissipation.

With lower signal loss, better dielectric properties, and high compatibility with next-gen tech, glass is leading the way for 5G, radar, and AI computing.