Printed Indium Inks for High-Density Chip Interconnects

Statement of the Problem or Situation that is Being Addressed – High Energy Physics detectors with large channel counts and fine granularity require higher-density interconnects. However, current assembly technology (flip-chip, etc.) uses solder-alloy bumps to interconnect devices that are stiff and cause warping of devices, possibly causing distortion in the detector. Current state of the art processing and patterning can achieve high resolution interconnects with submicron resolution on 2D surfaces but not around corners, edges and curved surfaces. Wire bonding is expensive and fragile. Statement of How this Problem or Situation is Being Addressed – Applied Nanotech proposes to use indium (In) inks that can be printed with sufficiently small pitch and feature sizes (<50 um) to achieve comparable bonding as solder bumps. Indium has the advantage of being malleable and compliant even at cryogenic temperatures. Printing of indium has advantages for printing circuits on 3D objects or curved surfaces, printing circuits around edges and corners without having to add bulky connections, and fill vias for through-wafer or through-carrier connections. Indium is also a superconducting material at 3.3K. What is done in Phase I – We propose to develop and demonstrate printed indium dots with the required size and pitch (25 um dots on 50 um pitch) using aerosol jet and/or screen-printing technology. We will demonstrate 3D printing of indium circuits and interconnects around corners and edges and demonstrate indium ink for via fill applications. ANI has already demonstrated an indium ink and together with Optomec, demonstrated printed indium with 150-micron feature size, lowering program risk. Commercial Applications and Other Benefits – Indium and indium-alloy solders are used in electronic packaging. Indium solders are generally screen printed or formed by solder ball jetting onto electronic packages with pitch of 100 µm or higher. The technology presented is nanoparticle-based indium ink and paste material that allows for the high-resolution, high-density printing over 3D surfaces, enabling smaller, lighterweight and higher-performance electronics for detectors or other electronics.