Alan J. Sangster

A Novel RF-Curing Technology for Microelectronics and Optoelectronics Packaging

A novel open waveguide cavity resonator for the combined variable frequency microwave (VFM) curing of bumps, underfills and encapsulants, as well as the alignment of devices for fast flip-chip assembly, direct chip attach (DCA) or wafer-scale level packaging (WSLP) is presented. This invention achieves radio frequency (RF) curing of adhesives used in microelectronics, optoelectronics and medical devices with potential simultaneous micron-scale alignment accuracy and bonding of devices using VFM technology. The open oven cavity can be fitted directly onto a flip-chip or wafer scale bonder and, as such, will allow for the bonding of devices through localised heating thus reducing the risk to thermally sensitive devices

Small signal bandwidth characteristics of a travelling-wave gyrotron amplifier

Small signal gain calculations on a travelling-wave gyrotron amplifier (gyro-TWA) show that for a low density uni-velocity beam, for which space charge forces can be neglected, moderate band widths, between 5% and 20%, can be attained at the expense of basic electronic efficiency. Interaction between the beam and the first four TEon modes of the circular cylindrical waveguide interaction region is considered and, for nil four cases, it is shown that at a given beam voltage mid current level an optimum bandwidth condition exists which is principally governed by the transverse-to-axial velocity ratio of the electrons in the uni-velocity gyrating beam.

Multiphysics simulation of microwave curing in micro‐electronics packaging applications

Purpose – This paper aims to present an open‐ended microwave curing system for microelectronics components and a numerical analysis framework for virtual testing and prototyping of the system, enabling design of physical prototypes to be optimized, expediting the development process.Design/methodology/approach – An open‐ended microwave oven system able to enhance the cure process for thermosetting polymer materials utilised in microelectronics applications is presented. The system is designed to be mounted on a precision placement machine enabling curing of individual components on a circuit board. The design of the system allows the heating pattern and heating rate to be carefully controlled optimising cure rate and cure quality. A multi‐physics analysis approach has been adopted to form a numerical model capable of capturing the complex coupling that exists between physical processes. Electromagnetic analysis has been performed using a Yee finite‐difference time‐domain scheme, while an unstructured fini...

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%.

A generalized analysis for a class of rectangular waveguide coupler employing narrow wall slots

A comprehensive analysis is presented which is applicable to the general class of waveguide couplers comprising a dissimilar pair of rectangular waveguide coupled by means of an inclined slot on the narrow wall of the primary waveguide. An entire domain moment method is used to solve a pair of coupled-integral equations for the tangential electric fields on the surfaces of the slot. Three typical examples have been examined to demonstrate the validity of the method. The numerical results are shown to be in good agreement with those obtained from independently procured theoretical evidence and measurements.

Optimization of an Open-Ended Microwave Oven for Microelectronics Packaging

A physically open, but electrically shielded, microwave open oven can be produced by virtue of the evanescent fields in a waveguide below cutoff. The below cutoff heating chamber is fed by a transverse magnetic resonance established in a dielectric-filled section of the waveguide exploiting continuity of normal electric flux. In order to optimize the fields and the performance of the oven, a thin layer of a dielectric material with higher permittivity is inserted at the interface. Analysis and synthesis of an optimized open oven predicts field enhancement in the heating chamber up to 9.4 dB. Results from experimental testing on two fabricated prototypes are in agreement with the simulated predictions, and demonstrate an up to tenfold improvement in the heating performance. The open-ended oven allows for simultaneous precision alignment, testing, and efficient curing of microelectronic devices, significantly increasing productivity gains.

Open ended microwave oven for flip-chip assembly

A novel open-ended microwave oven in the form of a waveguide cavity partially filled with dielectric is proposed for the microwave curing of bumps, underfills and encapsulants during flip-chip assembly. By adjusting the dimensions and the dielectric permittivity, a well defined resonance can be confined in the dielectric part with non-radiating evanescent decaying fields in the remaining of the cavity. Curing occurs by virtue of the energy stored in localized evanescent field maxima. The dielectric to air interface enhances the longitudinal electric field and therefore the cavity is designed to operate at a TM mode. Careful selection of the resonance order can control the locations of the electric field maxima (hot-spots) allowing for spatially selective heating. The open end design offers enhanced flexibilities for the simultaneous curing and alignment of devices for fast flip-chip assembly, direct chip attach (DCA) or wafer- scale level packaging (WSLP). Low power tests using heat sensitive film demonstrate clearly that selective heating in multiple locations in the open end of the oven is achievable.

Theoretical and Experimental Studies of Flip-Chip Assembled High-

This paper reports the theoretical and experimental studies of high-Q suspended microinductors produced by flip-chip assembly for multigigahertz RF integrated-circuit applications. The effects of device and substrate parameters on the Q factor of the inductor devices are studied by numerical simulation using Ansofts high frequency structure simulator electromagnetic field simulation package. Suspended inductor devices are realized using a flip-chip assembly method in which the inductor structures with the supporting pillars are fabricated on a low-cost polyimide thin-film carrier and then assembled onto a low resistivity (3-4 Omegaldrcm) silicon substrate by flip-chip bonding. Individual and 2times2 arrays of meander and spiral inductor designs have been successfully fabricated with air gap heights ranging from 15 to 31 mum. Maximum Q factors of ~15 and ~13 at ~1 GHz have been achieved for meander and spiral suspended inductor devices before pad deembedding. It is shown that the optimal air gap between the inductor and substrate surface is ~15 mum beyond which no further enhancement in the Q factor can be obtained for devices on low-resistivity substrates. The experimental results are in excellent agreement with that of theoretical simulation. The inductor assembly method requires minimal chip/wafer processing for integration of high-Q inductors.

Q

A novel open waveguide cavity resonator is presented for the combined variable frequency microwave curing of bumps, underfills and encapsulants, as well as the alignment of devices for fast flip-chip assembly, direct chip attach (DCA) or wafer-scale level packaging (WSLP). This technology achieves radio frequency (RF) curing of adhesives used in microelectronics, optoelectronics and medical devices with potential simultaneous micron-scale alignment accuracy and bonding of devices. In principle, the open oven cavity can be fitted directly onto a flip-chip or wafer scale bonder and, as such, will allow for the bonding of devices through localised heating thus reducing the risk to thermally sensitive devices. Variable frequency microwave (VFM) heating and curing of an idealised polymer load is numerically simulated using a multi-physics approach. Electro-magnetic fields within a novel open ended microwave oven developed for use in micro-electronics manufacturing applications are solved using a dedicated Yee scheme finite-difference time-domain (FDTD) solver. Temperature distribution, degree of cure and thermal stresses are analysed using an Unstructured Finite Volume method (UFVM) multi-physics package. The polymer load was meshed for thermophysical analysis, whilst the microwave cavity - encompassing the polymer load - was meshed for microwave irradiation. The two solution domains are linked using a cross mapping routine. The principle of heating using the evanescent fringing fields within the open-end of the cavity is demonstrated. A closed loop feedback routine is established allowing the temperature within a lossy sample to be controlled. A distribution of the temperature within the lossy sample is obtained by using a thermal imaging camera.

Suspended MEMS Inductors

A hybrid technique which combines the finite element method with the moment method is proposed for the analysis of radiating slots as used in slotted-waveguide array antennas. It differs from earlier contributions to this topic in that it formulates the field in the slots in terms of a functional, rather than a Greens function or combination of higher order waveguide modes which are generally used in conventional moment methods. It is, therefore, a promising candidate for the analysis of radiating elements of complex shape as used in, for example, circularly polarized and polarization selective slotted-waveguide array antennas. A conventional longitudinal slot in the broad wall of rectangular waveguide and a complex T-shaped slot in bifurcated waveguide have been modeled to demonstrate the validity of the hybrid technique. The numerical results are shown to be in good agreement with those obtained from independently procured theoretical evidence and measurement.