Low-Loss Glass Fiber Introduced for High-Speed Digital Systems

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L-Glass^TM, a new low-loss glass fiber yarn for printed wiring board (PWB) applications,
is AGY's answer to the rapid development of high-speed digital electronic systems.
Photo courtesy of AGY.

Circuit Designs Reported to Benefit from Higher Signal Speeds, Improved Signal Integrity

AIKEN, S.C.--In response to the rapid development of high-speed digital electronic systems, AGY, a major producer of glass fiber yarns and high-strength glass fiber reinforcements, has introduced L-Glass^TM, a new low-loss glass fiber yarn for printed wiring board (PWB) applications. The low dielectric constant (Dk) and low dissipation factor (Df) properties of L-Glass fiber are reportedly well-suited for designs requiring increased signal speeds and better signal integrity than traditional E-Glass/epoxy substrate materials.

"Substrate materials that provide low dielectric constant and low dissipation factor properties have become an essential element of high-speed digital systems, such as mobile communication base stations, high-end routers and servers, and high-speed storage networks," said Scott Northrup, director of new business development at AGY, in a statement released by the company. "As these systems move to higher processing speeds, substrates with low-loss properties are needed to ensure the speed and integrity of the signals."

Low-loss laminates for high-speed applications have traditionally been produced in one of two ways. In one method, a higher-performing epoxy resin system is used in conjunction with E-Glass--an approach that limits the achievable Dk and Df properties, according to AGY. The second method combines very low Dk/Df resins, such as PTFE, with ceramic filler and a much lower E-Glass content. Although these systems can achieve much lower Df/Dk properties, they are subject to high material and processing costs. The low glass loading also reduces the dimensional stability of the laminate. However, the use of L-Glass fiber is said to overcome these limitations by allowing epoxy resin systems to achieve much lower Dk/Df properties, and the PTFE-based systems to use a higher glass loading.

At 10 GHz, L-Glass fiber has a dielectric constant of 4.86 and a dissipation factor of 0.0050, whereas E-Glass has a dielectric constant of 6.81 and a dissipation  factor of 0.0060 at 10 GHz. The coefficient of thermal expansion (CTE) of L-Glass fiber is 3.9 ppm/°C, compared to 5.4 ppm/°C for E-Glass. According to AGY, this makes L-Glass fiber an attractive material for use in IC packaging, where CTE mismatches with silicon are magnified due to the thermal environment and can cause defects.

"L-Glass fiber is a cost-effective alternative to current systems," added Northrup. "The low- loss properties make it ideal for applications operating at the highest signal speeds and provide designers a compelling alternative to traditional materials."

AGY (www.agy.com), headquartered in Aiken, South Carolina, produces glass fiber yarns and high-strength glass fiber reinforcements used in a variety of composites applications. The company serves a diverse range of markets that include aerospace and defense, electronics, construction, and industrial.

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