Compliant Interconnects Based on Single Micrometer-sized Metal-Coated Polymer Spheres

• Published in: ACS applied materials & interfaces 2024-11, Vol.16 (44), p.60958-60966
• Main Authors: Huynh, Van Long, Aasmundtveit, Knut E., Nguyen, Hoang-Vu
• Format: Article
• Language: English
• Subjects: Applications of Polymer, Composite, and Coating Materials
• ISSN: 1944-8244; 1944-8252; 1944-8252
• DOI: 10.1021/acsami.4c12039

The rapid evolution of multifunctional electronics necessitates interconnection technologies appropriate for large dies with high-density and/or ultrafine pitch input/output pins. Existing technologies face numerous challenges, including demands for bonding equipment that can deliver extremely high force as well as thermo-mechanical stresses induced in the assembled packages due to mismatched thermal expansion of materials involved. This study proposes an approach to compliant interconnects comprising single micrometer-sized metal-coated polymer spheres, being joined to mating electrodes by sintering of Ag nano ink at low temperature (140 °C) and low pressure (∼15 mN/particle). Such an interconnection technology is expected to enhance the thermo-mechanical robustness of the assembled packages as well as be capable of high-density, ultrafine pitch interconnects. Our approach demonstrates control over conductive particles during assembly, achieving a 98% success rate in individual interconnects with a single captured particle. The use of sintered Ag not only secures free-standing particles on electrical pads (with an adhesion force above 2 μN) but also results in a 15% reduction in interconnect resistance, with measured resistance as low as 0.5 Ω, compared to interconnects without Ag ink. This method presents an alternative to metallurgical joints, particularly suited for high-density, ultrafine pitch applications, offering low bonding pressure and temperature, along with improved interconnect compliance to enhance the thermo-mechanical robustness of the packages.