Fabrication of Crack-Free LTCC Substrates with Large Aspect Ratio and Metal Pillar Embedded Cavities

Multilayer low temperature co-fired ceramics (LTCC) substrates have excellent electromechanical properties and flexible structural design, making them a preferred choice for fabricating high-density integrated microsystems. However, manufacturing complex embedded structures and large cavities in LTCC substrates still poses significant technical challenges. This work aims to improve the manufacturing techniques to address these issues and achieve reliable production of LTCC substrates with embedded metal pillar arrays and high aspect ratio microchambers. The side length of the chamber cavity is as large as 22 mm and the width-to-depth ratio is more than 38. Fugitive tapes are used as sacrificial materials. Several key fabrication processes are investigated, including laser drilling/cutting of single ceramic layers, sacrificial material drilling and firing, lamination, and low-temperature co-firing. A new two-step segmented lamination process has been proposed to prevent defects from occurring under isostatic pressure. Substrates free of cracks, delamination or collapses have been successfully fabricated and full evaporation of SVM has been achieved. The interlayer misalignment is smaller than 30 μm and the surface warpage is merely 13 μm The pressure resistance of the microchamber cavity in the substrate reaches 6 atm or more. Due to their excellent manufacturing quality, these LTCC substrates show great potential in high-efficiency liquid cooling and high-pressure applications.