Investigation of micromachined LTCC functional modules for high-density 3D SIP based on LTCC packaging platform

Micromachining of three dimensional (3D) micro functional structures or modules in interposers/substrates has been demonstrated as a prospective solution to high-density and heterogeneous 3D integration on package level. As follow-ups of the author's research jobs reported on the 62nd ECTC, which have initially revealed the capability of a unified LTCC packaging and laminate micromachining platform as such a solution, 3 types of LTCC micro functional modules based on the platform are investigated further, with their designing, fabrication, samples and validation/test results presented in this paper. The samples are prepared with 10~25 layers of green tapes by micromachining perforated 2.5D features into the individual layers, filling them with sacrificial materials, and laminating/sintering to form micron to millimeter scale 3D micro-structures. Sometimes, laser machining is used to finalize the 3D microstructure. The modules include: a) piezoresistive micro-accelerometer integrated with a preamplifier and passives, which responds linearly to ±4g (gravity acceleration) acceleration input, with a nonlinearity <;1%, 5~350Hz frequency response, and a resolving threshold of 10-4 g; b) 3D cooling microchannels, with a rectangle cross section (of 200μm height) and a length over 20mm, which can cut the peak temperature by over 100K at a heat flux of 3.2W/cm2 dissipated by thick film resistors emulating IC heating; additionally, an off-the-shell LED module is used as a practical vehicle to demonstrate the significance and efficiency of these channels by comparing their cooling effect with that of a bulky fan-cooling module as demanded by the LED supplier; c) RF MEMS passive and active functional structure for sub-millimeter and THz applications, including a filter sample with mid-band frequency at 82GHz and 5GHz pass bandwidth, and a method to enhance the radiation bandwidth of 60GHz patch antenna by shaping the laminates into sta- rcase and forming cavity coupling, both of which are validated with finite element full-wave analysis.