Sumanth Kumar Pavuluri

High Efficiency Wideband Aperture-Coupled Stacked Patch Antennas Assembled Using Millimeter Thick Micromachined Polymer Structures

Micromachined stacked patch antenna devices with high efficiency and wideband characteristics are reported. Polymer based fabrication and assembly processes have been developed in order to produce the stacked suspended antenna devices. Millimeter thick micromachined SU8 based polymer rings are used to create air gaps between the patches and the microwave substrate for optimized high efficiency operation. Thin film liquid crystal polymer (LCP) and polyimide substrates are used to support the radiating and parasitic patch elements. The polymer rings also form cavities to protect the patches and substrate from moisture and dust. The antenna structures are fabricated in layers and then assembled to obtain 3D devices. The antenna devices have been designed using an electromagnetic simulation package. The aperture coupled devices are impedance matched for wideband operation. RF measurements show wideband operation of the devices and the results are in good agreement with that of simulation. Typical gain and bandwidths are 7.8 dBi and 39% for a microstrip fed antenna device while they are 7.6 dBi and 44% for a CPW fed device. The predicted efficiency from the results of simulation is above 97% for the antenna devices.

A High-Performance Aperture-Coupled Patch Antenna Supported by a Micromachined Polymer Ring

An aperture-coupled high-gain microstrip patch antenna with wide bandwidth is reported. The slot-coupled antenna device was produced on a microwave PCB substrate with a suspended patch supported by a micromachined polymer ring structure. After the fabrication of the microstrip feed line and the coupling slot on the substrate and the patch on a polyimide film, two polymer rings of identical design were deposited on the microwave and the polyimide substrates respectively using a SU8 epoxy resin and the photolithography technique. The two polymer rings were then aligned and bonded together to obtain a suspended patch antenna for high-gain operation. The resultant height of the SU8 ring and hence the gap between the polymer and the microwave substrates was 1.5 mm. Reflection and radiation measurements were carried out to evaluate the performance of the antenna device. The results show that the device has a gain of 8.3 dBi at ~12 GHz and a -10 dB bandwidth of ~2.5 GHz or 19%. The simulated results are demonstrated to be in good agreement with measurement. The predicted efficiency of the device is about 98%.

Encapsulation of Microelectronic Components Using Open-Ended Microwave Oven

An open-ended microwave oven system is presented and characterized for the rapid encapsulation of microelectronic components. In situ real-time measurement of the temperature of the curing materials is carried out by an infrared pyrometer integrated in the microwave head of the oven. An automatic computer-controlled closed feedback loop has been used to measure the temperature in the curing material and modulate the system operating power to obtain predefined curing temperature cycles for efficient curing. Uniform curing of the encapsulant material is achieved with typical cure time of ~300s with a ramp rate of 1.66°C/s and a hold period of ~100s . Differential scanning calorimeter based measurement for the curing of the polymer dielectric indicates a near 100% degree of cure.

Label-free chemical/biochemical sensing device based on an integrated microfluidic channel within a waveguide resonator

In this article we propose a novel label-free chemical/biochemical sensing device based on a waveguide resonator with an integrated microfluidic channel. This device is intended for the characterisation and detection of cells and various chemical substances from within a variety of micro-litre test samples. This paper outlines the design of the prototype device and describes the fabrication of the microfluidic network and microwave resonator. Initial testing of the prototype at X-band is examined with promising results. Finally, we propose a Low Temperature Co-fired Ceramic (LTCC) integration scheme for the miniaturization of the device for use in the THz regime.

Integrated microfluidic capillary in a waveguide resonator for chemical and biomedical sensing

A novel microfluidic sensing device based on waveguide cavity filters is proposed for the characterisation, detection of cells in solution and chemical substances in micro-litre volumes. The sensor consists of a micromachined microfluidic channel within a waveguide-based resonator localised increased near-fields and could potentially be designed for different frequency regimes to improve the sensitivity. The present sensor has been proposed for fabrication in different manufacturing platforms and an initial prototype with a 100μm micromachined channel that is embedded within an X-band E-plane waveguide has been fabricated and tested. The design methodology for the microfluidic channel and the E-plane filter is also presented.

Fabrication and assembly of high gain MEMS antennas for wireless communications

Polymer based fabrication and assembly processes for producing suspended antenna devices have been developed. Stacked high gain patch antenna devices have been assembled using millimeter thick micromachined SU8 polymer ring spacers. Thin polyimide substrates (125 mum) were used for supporting the radiating and parasitic patch elements. The SU8 based polymer rings were used to create air space between the patches and the microwave substrate for high gain wide band operation. The polymer rings also form cavities to protect the patches and substrate from moisture and particles. An aperture coupled stacked patch antenna consisting of two patch elements was designed using an electromagnetic simulation package. The antenna device was fabricated in layers and then assembled to obtain a 3D antenna device. The detailed fabrication and assembly processes was described. RF measurements showed high gain wide band operation of the device and the results are in good agreement with that of simulation. The average gain and the bandwidth of the antenna device were determined to be 7.2 dBi and -40% respectively.

Experimental investigation of open-ended microwave oven assisted encapsulation process

An open ended microwave oven is presented with improved uniform heating, heating rates and power conversion efficiency. This next generation oven produces more uniform EM fields in the evanescent region forming part of the heating area of the oven. These fields are vital for the rapid and uniform heating of various electromagnetically lossy materials. A fibre optic temperature sensor and an IR pyrometer are used to measure in situ and in real-time the temperature of the curing materials. An automatic computer controlled closed feedback loop measures the temperature in the curing material and drives the microwave components to obtain predetermined curing temperature cycles for efficient curing. Uniform curing of the lossy encapsulants is achieved with this oven with typical cure cycle of 270 seconds with a ramp rate of 1°C/s and a hold period of 2 minutes. Differential scanning calorimeter based measurement for the pulsed microwave based curing of the polymer dielectric indicates a ∼ 100% degree of cure.

Application of Particle Swarm Optimisation to Evaluation of Polymer Cure Kinetics Models

A particle swarm optimisation approach is used to determine the accuracy and experimental relevance of six disparate cure kinetics models. The cure processes of two commercially available thermosetting polymer materials utilised in microelectronics manufacturing applications have been studied using a differential scanning calorimetry system. Numerical models have been fitted to the experimental data using a particle swarm optimisation algorithm which enables the ultimate accuracy of each of the models to be determined. The particle swarm optimisation approach to model fitting proves to be relatively rapid and effective in determining the optimal coefficient set for the cure kinetics models. Results indicate that the singlestep autocatalytic model is able to represent the curing process more accurately than more complex model, with ultimate accuracy likely to be limited by inaccuracies in the processing of the experimental data.

On the integration of microwave curing systems into microelectronics assembly processes

In microelectronics packaging applications a variety of thermosetting polymer materials is applied. Such materials are dispensed in a liquid form and are heated with the intent to cure them. Conventional processes often take several hours to bring the material up to temperatures which result in a significant rate of cure. An alternative approach to curing thermosetting polymers is the use of microwave energy, which has been shown to cure encapsulant materials in substantially shorter times. A recent innovation is the open-ended microwave oven proposed by Sinclair et al. [1]. This paper deals with the implementation of the open-ended microwave oven into a precision placement machine. Two test products for encapsulation and flip-chip serve as objective for microwave-assisted assembly. An integrated system setup including the open ended oven is presented. Modifications on the open-ended microwave oven are described and a concept for the development of an embedded microwave curing system is presented. Tests on curing encapsulant materials dispensed over a commercially available QFN were performed to determine post-process functionality of the package, with no evident detrimental effects.

Post cure behaviour of encapsulants for QFN packages processed by an open-ended single mode resonant microwave applicator

An open-ended single mode resonant microwave applicator has been developed for the curing of encapsulants materials used for microelectronic packaging. Post cure behaviour of Henkel™ E01080 encapsulant material has been studied by Differential Scanning Calorimetry (DSC), Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) analysis and Dynamic Mechanical Analysis (DMA). DSC based measurement of the microwave cured samples indicates a ∼ 99.2% degree of cure and a glass transition temperature, Tg, of 113°C for a sample cured at 150oC for 90 seconds. For the corresponding convection oven cured sample the degree of cure was found to be approximately 70% for the same duration of cure. The ATR-FTIR analysis showed no significant difference between the conventionally and microwave cured samples. Thermal ageing analysis performed on fully conventional and microwave cured samples showed similar ageing behaviour for both samples at a given temperature under Tg.