W. Kinzy Jones

Mechanical properties of Pb/Sn Pb/In and Sn‐In solders

The mechanical properties of eight solder alloys from the Pb‐Sn‐In‐Ag alloy systems were determined over the temperature range ‐200°C to 100°C, using uniaxial tensile tests, dynamic mechanical analysis (DMA), acoustic pulse methods and dilatometry. In general, the strength and elastic modulus of the alloys studied was inversely dependent on temperature. PbSn, PbIn and SnIn alloys were observed to turn superplastic with elongations over 100 per cent at temperatures of 50°C or above. The Pb‐based and In‐Sn eutectic solders possessed superplasticity at temperatures greater than 50°C. From these results, deformation and fracture processes are reviewed, and the appropriate fracture mechanism is proposed.

A miniature transformer/dc‐dc converter for implantable medical devices

This paper presents a new technique for the design of a miniature dc‐dc converter used in energy producing implantable devices such as defibrillators and advanced pacemakers. This converter is inserted in such a device and is used to boost the voltage from a low voltage implanted battery to high voltage energy storage capacitors in a short period of time. The stored energy is then delivered, when needed, through an energy delivery circuit in order to stimulate or defibrillate the heart. The converter takes the form of a flyback topology which includes a miniature transformer and a specialized control circuit. The transformer was designed using a new numerical synthesis method which utilizes finite elements and dynamic programming for predicting the geometries of the transformer’s magnetic circuit. The final transformer design satisfied the performance criteria and provided means for selecting the converter components. The obtained performance results for the transformer and the dc‐dc converter were in excellent agreement with laboratory performance tests.

Micro-Dispense Direct Printing for Thermal Management Structure Using LTCC

The microelectronic manufacturing industry has been seeking improved efficiencies and faster fabrication turn-around for decades. The demand for better thermal management has been increasing in recent years and better materials and new processing techniques have been emphasized. LTCC technology has demonstrated great potential for satisfying most performance, cost and processing requirements. A novel approach for LTCC is micro-dispense direct printing which can print a wide range of materials to include a variety of screen printable thick film conductors, thick film resistors, dielectric materials and solder. Those with experience in micro-dispensing recognize the size limitation using a dispensing approach and understand that the hope of achieving smaller line widths, smaller pad sizes, and precise placement of the material is challenging. nScrypt has demonstrated the ability to build a complete branching micro-channel structure using a micro-dispensing LTCC approach. nScrypt has also demonstrated how th...

The At-Temperature Mechanical Properties of Lead-Tin Based Alloys

The mechanical properties (elastic modulus, yield point, ultimate tensile strength, and elongation) of five Pb-Sn solder alloys (63Sn/37Pb, 62Sn/36Pb/2Ag, 96Sn/4Ag, 5Sn/95Pb, and 10Sn/90Pb) commonly used in electronic packaging have been determined over the temperature range of -200 to 150°C using uniaxial tensile test and an acoustic pulse method. It was found that the elastic moduli measured acoustically were 10 to 30 times greater than those measured mechanically, however, it is believed that the viscoelastic response of the materials may make the uniaxial tension test inaccurate for these types of alloys.

Electrochemical Modification of Superconductive Oxides

The electrochemical potential between highly electropositive cations and conductive oxides has been the basis for numerous electrochemical batteries (Li/MnCO2, Li/V2O5). A new cell, based on the superconductive oxide, YBa2Cu3Ox, as a cathode and lithium as an anode, has been developed. The cell exhibited high open-circuit voltage (2.8 volts) and long-term loaded voltage stability under low drain conditions at room temperature. The cell was discharged four months before destructive analysis. Room temperature operation was initially performed due to the use of a liquid electrolyte.

Effect of platinum metallization in cofired platinum / alumina microsystems for implantable medical applications

Typically, hermetic feedthroughs for implantable devices, such as pacemakers, use an alumina ceramic insulator brazed to a platinum wire pin. This material combination has a long history in implantable devices and is the desired structure due to the acceptance by the FDA for implantable hermetic feedthroughs. The growing demand for increased input/output (I/O) hermetic feedthroughs for implantable neural stimulator applications can be addresses by developing a new, co-fired platinum/alumina multilayer ceramic technology in a configuration that supports 300 plus I/Os, which is not commercially available. Different densification rate of platinum and alumina is the major issue in developing a high-density feedthrough. This difference in densification rate could create delamination and crack in feedthrough structure and decrease the reliability and degree of the hermeticty of the final assembly. In this paper different metallization were evaluated to minimize this difference. Additionaly the firing atmosphere...

Materials Interaction in Cofired Platinum /Alumina High Density Feedthrough for Implantable Applications

Neurostimulator applications will require much higher I/O feedthrough density for hermetic implantable enclosures, often greater than 100 I/O. This work evaluates the development of high-density platinum via structure cofired in alumina. The platinum was observed to melt when cofired at 1550°C, almost 200°C below its melting point, independent of the particle size (nano to micron size particles) or particle morphology. An analysis of the effect of particle size (nano to micron size Pt), firing atmosphere (air, hydrogen, inert), firing temperatures, intermetallic reactions and additives to control thermal expansion and adhesion strength was performed to evaluate and minimize this exothermic reaction. The interaction of platinum and alumina has been evaluated using X-ray diffraction and SEM.

A Direct Methanol Fuel Cell Using Cermet Electrodes in Low Temperature Cofire Ceramics

Low temperature cofired ceramics (LTCC) is becoming more integrated as ceramic microsystems. Microsystems allow the integration of numerous components, including embedded passives, high-density interconnects, highperformance thermal management systems, sensors and actuators, mechanical, fluidic, and optical components. The development of these systems have led to enhanced processing capabilities including enhanced properties by controlled sintering or the development of cavities and microelectromechanical structures using fugitive inserts which are removed during firing. LTCC devices have produced meso and macroscale channels, large volume cavities, microcavities, wick, and controlled porosity structures. LTCC has been used to fabricate the cavities and channels required in a direct methanol fuel cell (DMFC), using an externally attached membrane electrode assembly (MEA) which consists of a carbon matte anode with a platinum catalyst, a Nafion® proton exchange membrane (PEM) and a platinum/ruthenium cathode. The DMFC has a maximum thermodynamic voltage of 1.18 V at 25°C, defined by the anode and cathode half cell reactions:

Jet Impingement Cooling Using Micro Channels in Low Temperature Cofire Ceramic (LTCC) Substrates

With power densities near 200 W/cm2 for devices, new methods for thermal management from the heat generation at the die to heat removal to the ambient must be addressed. Signal interconnect and thermal management are often decoupled, with the I/Os from the substrate to the chip through flip chip solder balls and heat removed through the backside of the chip. However, interconnect substrates could provide both first level interconnect and fluid cooling thermal management. Providing micro channels in the same dimension as the interconnect pitch in the substrate allows for new and novel cooling methods to be integrated at the lowest level of chip assembly. X-Y micro channels less than 2 5 m wide and Z dimension channels 4 5 m wide were fabricated within the LTCC substrate. The integrated micro channels allow for direct jet impingement cooling. Initial thermal testing using single jet impingement demonstrated over a 200X reduction in thermal impedance.Copyright

Material Composition Changes During High Temperature Annealing and Electrochemical Migration Reliability

Metals can exhibit dendritic short-circuit growth caused by electrochemical migration in conductor-insulator structures, which may result in failures and reliability problems in microcircuits. The classical model of electrochemical migration has been well known for several decades. This process is a transport of metal ions between two metallization stripes under bias through a continuous aqueous electrolyte. Due to the electrodeposition at the cathode, dendrites and dendrite-like deposits are formed. Ultimately, such a deposit can lead to a short circuit in the device and can cause catastrophic failure. Recent investigations have demonstrated that not only metallic components, but also oxides from the isolating layers can take part in the formation of migrated shorts, after a chemical reduction process. Material design aspects need to clarify the correlation between material composition, processing, chemical bonding state, and electrochemical migration failure rate in isolating compounds: this is the scope of the present study.