Search

To facilitate a rapid response to the International Linear Collider (ILC) L-band development program at SLAC, a spare converter-modulator was shipped from LANL. This modulator was to be a spare for the spallation neutron source (SNS) accelerator at ORNL. The ILC application requires a 33% higher peak output power (15 MW) and output current (120 Amp). This presents significant design challenges to modify the existing hardware and yet maintain switching parameters and thermal cycling within the semiconductor component ratings. To minimize IGBT commutation and free-wheeling diode currents, a different set of optimizations, as compared to the SNS design, were used to tune the resonant switching networks. Additional complexities arose as nanocrystalline cores with different performance characteristics (as compared to SNS), were used to fabricate the resonant "boost" transformers. This paper will describe the electrical design, modelling efforts, and resulting electrical performance as implemented for the ILC L-band test stand.

Summary form only given. A solid state induction modulator was designed and operated for the Next Linear Collider accelerator project at SLAC (Stanford Linear Accelerator Center) to drive 8 X-band klystron. With the redirection of the NLC physics program, the remaining hardware from the DFM (Design for Manufacturability) modulator was combined with existing pulse transformers to fabricate two hybrid solid state induction modulators, one to drive two XK5 klystrons at 420 kV 400 A 1.5 mus and a second modulator to drive a single 5045 klystron to 360 kV 430 A 3.5 mus. These modulators use induction cells to drive a conventional pulse transformer. Both modulator are smaller and operate at a lower operating voltage than a equivalent modulator using thyratron and PFN. The modulator have been fabricated, tested, and are in operation. The design, implementation, and results will be describe in the paper.

Evanescently coupled waveguide arrays are written in fused silica using femtosecond laser pulses. Array supermodes are tailored by adjusting the writing conditions of a common central core and agree with scattering matrix method simulations.

A compact, water cooled, high power switch for the Superconducting Module Test Facility (SMTF) long-pulse klystron modulator has been constructed and implemented at the Fermi National Accelerator Laboratory (FNAL). This solid-state switch is composed of six series devices, each having a rating of 4.5 kV and 2000 Adc. Latest generation, press-pack IGBT modules are utilized to reduce the physical size and complexity of the switch assembly. The new switch and its associated controller provide a high degree of redundancy and fail-safe operation, which meets the modulator requirements. This paper describes the general switch assembly, IGBT protection and control schemes, and test results.

As the switching capabilities of solid-state devices increase, these devices are being incorporated into modulator designs for high voltage accelerator applications. Solid-state modulators based on inductive adder circuit topology have demonstrated great versatility with regard to pulse width and pulse repetition rate while maintaining fast pulse rise and fall times. Additionally, these modulators are capable of being scaled to higher output voltage and power levels. An explanation of the basic circuit operation will be presented as well as test data of several different hardware systems.

The next linear collider (NLC) accelerator proposal at Stanford Linear Accelerator Center (SLAC) requires a high efficiency, highly reliable, and low cost pulsed power modulator to drive the X band klystrons. The present NLC RF compression technique needed a modulator to drive 4 Klystrons at 400 kV, 1300 A for 1.6 muS at 60 PPS (>500 megawatt pulse, 80 kW average). A prototype NLC solid-state induction modulator was modified to drive this new klystron array. The prototype induction modulator utilizes a three-turn secondary with 76 single "fraction turn" primary to produce the 400 kV pulse. The design, testing and operational experience will be discussed

At SLAC, research and development for the next linear collider (NLC) is progressing. The 8-Pack project is a test stand in which key NLC components will be developed. Presently the setup is such that an induction modulator [R. L. Cassel et al., The Prototype Solid State Induction Modulator for SLAC NLC] will generate 400 kV, 1200 A, and 1.6 /spl mu/s flattop pulse to drive four XL4 X-band klystrons. This requires the use of 76 high power IGBT modules operating in parallel at 3600 A and up to 2200 V each. IGBT switching speeds and short circuit protection from klystron arcs are major concerns. This paper describes a gate drive circuit with a new method to protect IGBT modules under short circuit conditions. Using a dI/dt control technique, the gate drive circuit enabled the Mitsubishi module CM600HB-90H to switch 4000 A at speeds up to 10 kA//spl mu/s in normal operation, while holding the short circuit peak-current to about 8000 A. Results from the single IGBT test and the 8-Pack Modulator prototype will be presented.

The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed power modulator to drive the X band klystrons. The present NLC envisions a solid state induction modulator design to drive up to 8 klystrons to 500 kV for 3(S) at 120 PPS with one modulator (>1000 megawatt pulse, 500 kW average). A prototype modulator is under construction, which will power 4 each 5045 SLAC klystron to greater than 380 kV for 3(S) (>600 megawatt pulse, >300 kW ave.). The prototype induction modulator utilizes a three-turn secondary to produce the 500 kV pulse. The design, installation and testing of the three turn secondary and its effect on rise time and fault conditions is discussed. The design and implementation of a snubber to improve the arcing condition are covered.

As part of an improvement project on the linear accelerator at SLAC, it was necessary to replace the original thyratron trigger generator, which consisted of two chassis, two vacuum tubes, and a small thyratron. All solid-state, fast rise, and high voltage thyratron drivers, therefore, have been developed and built for the 244 klystron modulators. The rack mounted, single chassis driver employs a unique way to control and generate pulses through the use of an asymmetric SCR, a PFN, a fast pulse transformer, and a saturable reactor. The resulting output pulse is 2 kV peak into 50 /spl Omega/ load with pulse duration of 1.5 /spl mu/s FWHM at 180 Hz. The pulse risetime is less than 40 ns with less than 1 ns jitter. Various techniques are used to protect the SCR from being damaged by high voltage and current transients due to thyratron breakdowns. The end-of-line clipper (EOLC) detection circuit is also integrated into this chassis to interrupt the modulator triggering in the event of a high percentage of line reflections occurring.

Retrieval information about soil moisture and roughness from remotely sensed data is of great interest for agricultural soil management. In fact, these two physical parameters are crucial for predicting erosion rates within agricultural watersheds during the rainfall season. In this context, there exists a strong interest to assess the potential of SAR (synthetic aperture radar) images to provide information regarding to these two physical surface parameters with periodic acquisitions. Nevertheless, one major source of error in the quantitative estimate of these parameters is the presence of the speckle within the scene registered by SAR instruments. To overcome this difficulty many filtering techniques have been developed for reducing this multiplicative noise. However, as to the authors' knowledge, no study has analysed the sensitivity of these speckle filtering approaches on the estimates of soil moisture and roughness. Consequently, the authors propose in this paper to quantify the influence of several speckle filtering methods on the assessment of these agricultural soil parameters.

Recent experience with SLC (Stanford Linear Collider) has shown that very fast, ferrite-loaded, transmission-line, beam-kicker magnets can cause significant and undesirable distortion of a 1.5-2.5-kA, 20-40-kV pulse as it travels through the magnet. In general, there is a net lengthening of the pulse, with increases in its rise and fall times, a decrease in amplitude, and an unsymmetrical rounding of the flat top. A number of practical design considerations are discussed in terms of equivalent circuits, magnet circuit dispersion and dissipation, undesired circuit shunting and coupling, high-voltage breakdown problems and high-order-mode losses that lead to beam tube heating. These effects are linked to the properties of the materials, the presence of radiation, and realizable magnet topologies. Measurements and calculations of some of these characteristics for several magnet design are reviewed. >

Silver filled epoxy is the most common type of adhesive used to attach Si chips to metal leadframes in plastic packages. However, with the attachment of larger die sizes (2 cm length on the side or larger) to thin copper lead frames now coming into routine use, most of the current adhesives were not reliable for these applications. Major technical issues of these materials are: stress-induced Si fracture; delamination at molding and post molding; device failures under pressure cooker tests and thermal shock tests; thermal/hydrolytic stability of adhesive; and narrow processing window. A novel thermoset cyanate ester die-attach paste has been developed to address the above issues. The paste is suitable for use on conventional dispensing equipment. This material can be cured in less than 60 seconds at 200/spl deg/C and does not generate any appreciable weight loss during cure. As a result, the same fast cure profile can be utilized for all die sizes. In this paper, we review the chemical and physical characteristics of the material and its functional performance as a die-attach media. The combination of a lower modulus of rigidity, about 400 MPa (vs. 1000 Mpa for conventional epoxies) and thermal stability at temperatures well above 300/spl deg/C has given the material excellent adhesive strength, even at 300/spl deg/C, as well as imparting very low stress on the die. Our data indicated the stress level is not sensitive to curing methods such as fast-curing on a heater block or slower-curing in a box oven. The stress level also does not change after long term high temperature at 150/spl deg/C or temperature cycles between -65/spl deg/C to 150/spl deg/C. >

A fluxless repair process for flip-chip multichip modules (MCMs) is demonstrated. The process includes steps for removing defective chips, reducing and leveling solder at the chip site, and retacking a new, good chip in its place. After chip removal, most of solder remained on the bonding pads. A technique has been developed to remove excess solder and to level the pads to a consistent bump height. Experimentation has shown that the wick chip reduced remaining solder bump heights to about the same height as the virgin substrate. New chips were then retacked to the leveled sites and the modules were heated in a controlled atmosphere to reflow the solder joints. Modules repaired using this technique have shown yields similar to those obtained during the initial assembly stages in electrical continuity tests. >

The damping ring kickers for the SLAC Linear Collider (SLC) must meet extreme requirements on rise and fall time, flatness, time and amplitude jitter and drift, voltage, repetition rate, and reliability. After several generations of improvements to the pulsers, magnets, and controls and evolution in the understanding of the requirements, the kicker systems are no longer a serious constraint on SLC performance. Implications for future linear colliders are discussed. >

A fast solid-state pulse generator used as a thyratron grid driver for kicker pulsers, has been developed and built with power MOSFETs and a transmission line transformer. The MOSFET, pulsed on and off by a pair of P-N channel HEXFETs, switches charged capacitors into the transformer connected in parallel on one end and in series on the other end to step up the voltage. The resulting output pulse parameters are 2-kV peak (into 50 Omega ), 13-ns, risetime (10-90%), 250-ns duration, and less than 50-ps pulse-to-pulse jitter. Various methods are employed to protect the MOSFETs from thyratron arc back, including the use of TransZorbs and a magnetic diode. >

The klystrons for the next-generation linear collider (NLC) are designed to operate at 500 kV, and have a microperveance of 0.75/spl times/10/sup -6/ AV/sup 3/2/, or 265 A of beam current. Two klystrons are planned to be driven in parallel by one pulse modulator with a 1:14 step up transformer. The impedance of the pulse forming network (PFN) for the modulator is therefore 4.8 /spl Omega/, while the charge voltage is 71.5 kV. The pulse width is 1.5 /spl mu/s, so the total capacitance to be charged is 0.156 /spl mu/F. The maximum repetition frequency is 180 Hz. The power supply required to charge the PFN is thus an 80 kV, 100 kW capacitor charging power supply. Because of the large number of klystrons used in the NLC, up to approximately 10,000, there are several additional requirements which the capacitor charging supply must meet. The most important of these requirements is efficiency, which must be approximately 95% or better. Next is cost, followed by reliability (greater than 50,000 hour MTBF), maintainability, ease of connection, disconnection and transport. Several circuit topologies designed to meet the charger requirements have been studied. Detailed analysis has been performed on a flyback power converter, a series resonant power converter, and a command resonant power converter. Advantages and disadvantages of each are discussed.

Each of the eight 1.2 MW RF klystrons for the PEP-II storage rings require a 2.5 MVA DC power supply of 83 Kv at 23 amps. The design for the supply was base on three factors low cost, small size to fit existing substation pads, and good protection against damage to the klystron including klystron gun arcs. The supply uses a 12 pulse 12.5 KV primary thyristor "star point controller" with primary filter inductor to provide rapid voltage control, good voltage regulation, and fast turn off during klystron tube faults. The supply also uses a unique secondary rectifier, filter capacitor configuration to minimize the energy available under a klystron fault. The voltage control is from 0-90 KV with a regulation of

A new type of die attach material based on a modified olefin thermoset polymer has been developed. Due to its hydrophobic molecular structure, moisture absorption is inherently very low. For example, it absorbs less than 0.05% moisture at 85/spl deg/C/85% RH/168 hrs. Even in HAST test (150/spl deg/C/85% RH/168 hrs.), moisture content is only 0.1%. The olefinic polymer is formulated as a low stress, electrical and thermally conducting paste adhesive. Its other principal features include good processability, less resin bleed and low temperature cure. The new die attach candidates were evaluated using 208 LD PQFP packages with standard epoxy molding compounds. This type of package passed moisture reliability tests at level 3. At JEDEC level 1, there were still package cracks and delaminations at the mold compound interfaces. However, no die attach delamination was observed. These studies clearly demonstrated the need for replacing conventional epoxies with low moisture absorbing polymers for die attachment and encapsulation in order to produce moisture insensitive packages. In summary, the new olefinic thermoset adhesives have shown promise for many die attach applications. These materials will provide important process and reliability improvement for advanced device packaging.

Polycyanate based die attach adhesives have found increased popularity for many applications including hermetic as well as plastic molded IC packages. Principal advantages of cyanate thermoset are high heat resistance, low outgassing of volatiles, and easily modified to satisfy various application requirements. This paper reviews the development of various types of adhesives designed to meet advanced semiconductor packaging requirements. Generally speaking, the hard, rigid adhesives are used on rigid, non-bending substrates such as alumina, copper heat sink, etc. While the soft, flexible adhesives find applications for flexible substrates such as thin copper leadframes, polymer laminates.

Novel adhesive, using in-line process, has been shown to reduce adhesive cure cycle time from 70 minutes to as little as 44 seconds at 160/spl deg/C. Throughput improvement of 60% using existing box ovens and no increase in floor space has been confirmed on production equipment. The adhesive is based upon a modified cyanate ester resin, which cures to form a triazine polymer with excellent temperature stability and unique moisture properties. It generates 75% less outgassing during cure than typical snap sure epoxies, which reduces contamination of the chip, leadframe and oven chamber. Live device reliability, equivalent to standard box oven, has been demonstrated for the new snap cure adhesive using in-line cure, as well as, fast box oven process. Material, processing and qualification data is summarized and compared to epoxies for analog and logic ICs packaged in SOIC, PDIP, and PLCC body styles. The material has been fully qualified and is in production use.

The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed-power modulator to drive the 500 KV, X band klystrons. A Solid State Induction Modulator to power the klystrons is under development uses high voltage 3.3 kV high current (3 KA pulses for 3 /spl mu/S) IGBT modules develop for traction and electric train application. Testing of these IGBTs under pulsed conditions have been very successful, however the IGBTs failed under short circuit testing. Unpredicted current and gate waveforms and eventual IGBT failures occur when short circuit tests were performed into extremely low short circuit inductances (< 50 nH). The failures appeared to be gate related and not the anticipated collector to emitter overvoltage. The internal connection structure of the IGBT package was analyzed and its performance simulated, which resulted in an understanding of the strange current response under short circuit and the resulting failures. Test results will be presented, IGBT package layout, circuit simulation and recommendation for modification to the standard IGBT layout to improve performance of IGBT's under extremely low inductance short circuits.

A paste adhesive system based on a modified cyclic olefin thermoset (MCOT) polymer was first introduced in 1997. MCOT consists of blocks of cyclic olefin (rigid) and linear olefin (soft). Due to its hydrophobic molecular structure, moisture absorption is inherently quite low, typically less than 0.1%; an order of magnitude lower than that of epoxies. Although its adhesive strength is less than that of epoxy, the MCOT based adhesive has been successfully used as die attach material for BGA packages. This paper describes our continued technology development to enhance the adhesion performance of MCOT material. The low adhesive strength is caused by the lack of reactive functional groups in the MCOT structure. Some desirable organic functional groups were identified, and grafted onto both the linear and cyclic olefin structures of MCOT. Using a Neural Network Analyzer model, we examined the effects of several variables such as the amount and type of reactive groups, and polymer molecular weight against key outputs such as adhesion, % moisture absorption, and viscosity. An optimized resin formulation with respect to these key elements was derived from this modeling approach. The improved MCOT composition shows at least twice the adhesion strength on various substrates with minimal impact on moisture absorption. Adhesion values are now comparable to epoxy. The new material with a unique combination of ultra low moisture and high adhesion appears to have the versatility to address a broad range of applications. It may promise to play an important role of the total material solution for many contemporary problems in polymer based packages.

Summary form only given. A test is ongoing at the Stanford Linear Accelerator Center (SLAC) where a solid state induction modulator is driving a SLAC 5045 Klystron. The modulator generates a 22kV, 6kA pulse which is stepped up by a 15:1 transformer that is a part of the Klystron pulse tank. The modulator's pulse duration is adjustable up to the volt-second limit of its cores, and it is capable of a pulse repetition frequency up to 120 Hz. The modulator's design, construction, and the experimental results are the focus of this paper.

A new gate drive for high-voltage, high-power IGBT has been developed for the SLAC NLC (Next Linear Collider) Solid State Induction Modulator. This paper describes the design and implementation of a driver that allows an IGBT module rated at 800 A/3300 V to switch up to 3000 A at 2200 V in 3 /spl mu/s with a rate of current rise of more than 10000 A//spl mu/s, while still being short circuit protected. Issues regarding fast turn on, high de-saturation voltage detection, and low short circuit peak current are presented. A novel approach is also used to counter the effect of unequal current sharing between parallel chips inside most high-power IGBT modules. It effectively reduces the collector-emitter peak currents and thus protects the IGBT from being destroyed during soft short circuit conditions at high di/dt.

The Stanford Linear Accelerator utilizes over 250, 5045 klystrons which are at driven by 35 year old modulator utilizing standard PFN capacitors, thyratrons and conventional pulse transformer to generate a 3.5 /spl mu/s pulse of 350 kV, 400 A, at 120 Hz. The proposal is to use a 10 section solid state induction modulator to replace the existing PFN/thyratron modulator, and drive the klystron using the existing conventional pulse transformer. The induction modulator utilizes a pulse transformer similar to an induction accelerator driven by solid state high voltage IGBT switches and DC capacitors. The performance and test results of the IGBT, induction modulator driving a conventional transformer with a 5045 klystron load is discussed.