Wafer-Level Packaging Method for RF MEMS Applications Using Pre-Patterned BCB Polymer

Abstract

A radio-frequency micro-electro-mechanical system (RF MEMS) wafer-level packaging (WLP) method using pre-patterned benzo-cyclo-butene (BCB) polymers with a high-resistivity silicon cap is proposed to achieve high bonding quality and excellent RF performance. In this process, the BCB polymer was pre-defined to form the sealing ring and bonding layer by the spin-coating and patterning of photosensitive BCB before the cavity formation. During anisotropic wet etching of the silicon wafer to generate the housing cavity, the BCB sealing ring was protected by a sputtered Cr/Au (chromium/gold) layer. The average measured thickness of the BCB layer was 5.9 μm. In contrast to the conventional methods of spin-coating BCB after fabricating cavities, the pre-patterned BCB method presented BCB bonding layers with better quality on severe topography surfaces in terms of increased uniformity of thickness and better surface flatness. The observation of the bonded layer showed that no void or gap formed on the protruding coplanar waveguide (CPW) lines. A shear strength test was experimentally implemented as a function of the BCB widths in the range of 100–400 μm. The average shear strength of the packaged device was higher than 21.58 MPa. A RF MEMS switch was successfully packaged using this process with a negligible impact on the microwave characteristics and a significant improvement in the lifetime from below 10 million to over 1 billion. The measured insertion loss of the packaged RF MEMS switch was 0.779 dB and the insertion loss deterioration caused by the package structure was less than 0.2 dB at 30 GHz.

Research Status and Development Trend of MEMS Switches: A Review

“…(3) High packaging cost. The packing of the switch has always been a conundrum [167,168]. The packaging cost of switches is often much higher than the manufacturing cost, which restricts their mass quantification.…”

Scalable Batch Transfer of Individual Silicon Dice for Ultra-Flexible Polyimide-Based Bioelectronic Devices

“…After determination of their exact position, the dice were subjected to shear test. The shear strength was measured to be 58.1 ± 13.7 MPa, a value comparable to dice attached with benzocyclobutene (BCB), a commonly used adhesive for attachment [19,20]. After accelerated aging at 60 °C in PBS the average shear strength drops to 15.2 ± 10.5 MPa.…”

A Simple Method for Fabricating Ink Chamber of Inkjet Printheads

“…The thermal bonding technique requires a high temperature and high pressure in the bonding process, leading to deformation and damage of the structure [ 24 ]. Although the adhesive bonding approach has some disadvantages, such as the need to design the joints in the proper way or to have adherent substrates, the requirement for specific clamping devices to fix the joint during cure, and the requirement for specific processing (surface pretreatment, curing, process control) [ 25 ], the adhesive bonding technique offers several advantages, including a simple process, lower cost, short time, and no need for heating when compared with the above two technologies [ 26 , 27 , 28 ].…”