Through-Glass Vias for Glass Interposers and MEMS Packaging Applications Fabricated Using Magnetic Assembly of Microscale Metal Wires

Citation

M. J. Laakso, S. J. Bleiker, J. Liljeholm, G. E. Mårtensson, M. Asiatici, A. C. Fischer, G. Stemme, T. Ebefors, and F. Niklaus, "Through-Glass Vias for Glass Interposers and MEMS Packaging Applications Fabricated Using Magnetic Assembly of Microscale Metal Wires," IEEE Access, vol. 6, pp. 49938-49950, 2018.

Keywords

• Through-glass vias (TGVs)
• Magnetic assembly
• Glass interposers
• MEMS packaging
• Wafer-level packaging
• Thermal expansion mismatch
• Coefficient of thermal expansion (CTE)
• Solder bumps
• Nickel wires
• Spin-on glass (SOG) 

Brief

The article presents a novel method for fabricating through-glass vias (TGVs) using magnetic assembly of metal wires, enabling low-resistance vertical electrical connections in glass substrates for advanced packaging applications like glass interposers and MEMS packaging. The sources describe the fabrication process, characterize the electrical resistance of the TGVs, and analyze the thermal expansion properties of different metal-glass combinations for optimal thermal compatibility. 

Summary

This article, published on August 1, 2018, presents a method for creating vertical electrical connections through glass substrates, known as through-glass vias (TGVs). The authors utilize a magnetic assembly technique to fill via holes in glass substrates with metal wires, offering an alternative to conventional methods like super-conformal electroplating, which is challenging to implement on glass due to its rough via-hole sidewalls.

Here's a summarized breakdown of the article:

• Background: TGVs are crucial for advanced packaging technologies in electronics, offering advantages over silicon-based through-silicon vias (TSVs) such as low electrical losses, reduced coupling, and cost-effectiveness. However, fabricating high-quality TGVs in glass is difficult due to the challenges in creating smooth via holes suitable for conventional metal filling techniques.
• Magnetic Assembly Method: This article demonstrates the use of magnetic assembly to overcome the limitations of existing TGV fabrication methods. The process involves magnetically pulling ferromagnetic metal rods into pre-fabricated via holes in a glass substrate. The rods are then fixed in place using spin-on glass (SOG). This method allows for the creation of completely filled TGVs, even in blind holes, which is advantageous for achieving thin substrates.
• Addressing Challenges and Demonstrating Functionality: The article addresses the challenge of metal rods disassembling from the glass via holes (due to their conical shape and low aspect ratio) by employing multiple magnets during assembly. This ensures a continuous magnetic field, preventing disassembly before the rods are secured with SOG. The researchers successfully demonstrate the fabrication of TGVs with a typical resistance of 64mΩ, comparable to other reported metal TGVs. They also showcase the feasibility of depositing solder paste directly onto the TGVs using a jetting technology, demonstrating potential for high-density integration.
• Parallelization and Thermal Expansion Considerations: To improve fabrication throughput, the article explores the parallelization of the magnetic assembly process using multiple magnets simultaneously. Results indicate that this approach can significantly reduce wafer-scale assembly time. Additionally, the article analyzes the thermal expansion compatibility of different metals (suitable for magnetic assembly) with various glass substrates. This is crucial for minimizing stress and ensuring the reliability of TGVs, particularly those without a hollow center. The analysis identifies Kovar and Invar as promising materials, exhibiting good thermal expansion matching with glass substrates like borosilicate and fused silica.

Overall, the article highlights magnetic assembly as a promising technique for fabricating high-quality TGVs. The authors address key challenges,  demonstrate functionality, and explore avenues for improving efficiency and reliability.

Origin: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8424149