Gold Ball Research Articles

Conformation of Lac repressor tetramer in solution, bound and unbound to operator DNA.

We tested whether the Steitz et al. [(1974) Proc. Natl. Acad. Sci. U.S.A., 71:593-597] model of lactose repressor (LacR) (14 x 6.0 x 4.5 nm) represented the shape of free or operator-bound LacR in solution. The model predicts a 14 nm length for bound LacR. Direct measurement, using Pt-C shadow width standards, was 9.6 +/- 0.2 nm long. Using the Steitz model, we generated a distribution of measurements and converted them into a distribution of shadow widths using gold ball standards. Direct measurement of LacR produced a narrower shadow width distribution with a larger mean size than the Steitz model predicted. Measurement along two orthogonal axes of negatively stained LacR images generated a size distribution, also converted into a shadow width distribution using the gold ball standards. Since the experimental shadow width distribution exactly matched the shadow width distribution derived theoretically from negatively stained LacR, our negative-stained images are representative of LacR's conformation in solution. Approximately 56% of negatively stained LacR had a V-shaped fold around an axis orthogonal to its length, bringing the DNA binding domains of each dimer adjacent. This open end of the V binds single operator DNA. The other 44% of the LacR tetramer is in the extended form with its DNA binding sites at opposite ends. Although the V-shaped conformation has a closed hinge with the dimers associated along a side, the extended open-hinged state remains important since LacR must bind two distant operator sites for full repression. Our measurements predict the normal presence of both conformations in nearly equal amounts, suggesting that both are equally active in repressing the lac operon.

Quantification of particle sizes with metal replication under standard freeze‐etching conditions: A gold ball standard for calibrating shadow widths was used to measure freeze‐etched globular proteins

The real size of platinum-carbon (Pt-C) replicated particles is not directly equivalent to either its metal-coated diameter or its shadow width. This paper describes two indirect methods, shadow widths and coated particle diameters, for determining a particle's actual size beneath a Pt-C replication film. Both produce equivalent measurements using the same standardized conditions: 2.3 nm Pt-C films deposited at a 45 degree angle on an approximately -100 degrees C surface in a 10(-6) torr vacuum. For the first method, gold balls nucleated in a partial pressure of helium and deposited on flat indirect carbon films (root mean square roughness of 0.8 nm) on 400 mesh grids were used as test particles for calibrating shadow widths as a function of particle size. The gold ball test specimens were replicated, and a distribution of Pt-C shadow widths orthogonal to the Pt-C deposition direction was measured and averaged for gold balls 1.5 +/- 0.25 nm, 2.0 +/- 0.25 nm, etc. The diameter of each gold ball was measured within the Pt-C film along with its shadow width because the Pt-C did not obscure or adhere well to the gold. The shadow width distributions for each gold size do not differ significantly from log normal. Two proteins, the lactose repressor and the mitochondrial ATPase, F1, were also used as replication test objects. Negative staining of both proteins was conducted to measure their average diameters. In the second method, a distribution of Pt-C-coated lac repressor diameters perpendicular to the shadow direction was measured. The Pt-C film thickness measured on the quartz crystal monitor was subtracted from the average metal-coated protein diameter to obtain the lac repressor's diameter. The Pt-C-coated particle diameter distributions also did not differ significantly from log normal. While doing this work it was discovered that outgassing the Pt-C electron gun greatly affected Pt-C film granularity: 19 sec produced a high contrast, granular Pt-C film, whereas 120 sec yielded a low contrast, less granular Pt-C film. Both gold balls and protein particles were subjected in separate experiments to either 19 or 120 sec of outgassing of the Pt-C gun prior to Pt-C replication. Outgassing had a profound effect on the average size of the Pt-C shadow widths on both gold and protein particles. The Pt-C gun outgassing procedure also determined the smallest replicated particle that could be resolved. The frequency of some smaller gold ball sizes detected after replication was reduced disproportionately with 19 sec vs. 120 sec outgassing. However, Pt-C gun outgassing did not affect the average measured diameter of the Pt-C-coated protein particles. The "geometric assumption" that each metal-coated particle creates a shadow width the same size as the metal-coated particle diameter was tested using a globular protein. Pt-C replication of protein particles at a 45 degree and 20 degree angle could not confirm the geometric assumption because an average shadow width was always significantly larger than its average Pt-C-coated particle diameter. A model for how the large shadow widths are formed is presented. Gold balls were also replicated at a 45 degree angle with current high resolution conditions at a substrate temperature of -185 degrees C, and the results of these replicas were compared to the results reported here at approximately -100 degrees C.

Thermosonic bond contacts with gold wire to YBa2Cu3O7 microstructures

A reliable method for making contacts to YBa2Cu3O7 microstructures is ultrasonic bonding. However, the application of bonding to YBa2Cu3O7 microstructures can lead to severe problems especially in the case of gold ball bonds. The required ultrasonic power for gold ball bonds is higher than for aluminium wedge bonds due to the harder gold wire. We find that high ultrasonic power can degrade or even destroy YBa2Cu3O7 microstructures, such as microbridges, Josephson junctions and superconducting interference devices (DC SQUIDS). This problem can be overcome by using thermosonic bonding at a sample temperature of 150 degrees C. With heating the necessary ultrasonic energy can be reduced significantly, leaving the microstructures intact. We investigate the influence of the ultrasonic power, bonding time and bonding force on the properties of the resulting bond contacts.

The in-process bond shear test: Its relationship to ball bond reliability and its application to the reduction of wirebond process variation

In this study, a strong relationship is found between in-process (post wirebond) bond shear test results on gold ball bonds and post-process, post-board mount wire pull results. The shear test results detect clear differences in shear strength and failure mode between two types of bond pad structures. Significant variation due to the level of ultrasonic power used in bonding was also found. The subsequent wire pull results obtained from units receiving full package assembly and simulated customer board mount agreed with the in-process shear findings of both pad structure and bonding process effects. The relationship between inprocess shear and ball bond reliability in a finished package may lead to many opportunities to improve package reliability by reducing variation in the wirebond process. As an example, an application of in-process shear results is provided that studies the effects of capillary changes on wirebond process variability.

Electromigration: Investigation of heterogeneous systems

Electromigration is a phenomenon where atoms are driven from their lattice positions due to an electric current. In general two types of electromigration systems can be distinguished: the heterogeneous system, in which electromigration failure occurs at the interface of two distinct parts on the interconnection while in the second, homogeneous case the failure occurs within the interconnection itself. The first type of electromigration is reported in this study and off-chip gold ball bonds on aluminium metallization are used as an example. In-situ electrical measurements of the resistance change as a function of time with different temperature and current stresses are performed. A good understanding of the kinetics of the resistance change could be obtained which helps in the characterisation of the processes active during the degradation of the interconnections.

A Study of the Copper Wire Ball Bonding Processes

ABSTRACTCopper ball bonding is a new technology which is expected to replace the traditional gold ball bonding and paid attention in woled recently, the technology is very important to reduce cost and improve reliability of microelectronic components. In this paper, the copper wire ball bonding processes have been studied by means of the MW-EFO metal wire ball forming device and the JWYH-2 thermosonic ball bonder. The bond strength of the ball bond under varied ultrasonic power and bonding time have been tested. The tested results show that the maximal strength of copper ball bond can be over 20g, it has advantage over the gold wire ball bonding. In this paper, the deformation process of the copper ball bond has been analyzed and viewed by SME.

Intermetallic and void formation in gold wirebonds to aluminum films

Gold ball bonds attached to either pure Al films or Al films with Cu and Si additions were annealed at temperatures in the range 77–277°C for periods of up to 3,000 h and then shear tested. The resulting fracture surfaces were observed to change progressively with time and temperature of annealing. The intermetallic phases and voids present after each annealing treatment were characterized by microscopic examination of the bond cross sections. Shear test results are discussed in terms of the observed microstructures.

The effect of high-temperature intermetallic growth on ball shear-induced cratering

The effect of the growth of additional gold-aluminum intermetallics at elevated temperatures on ball shear-induced silicon cratering is investigated. A mechanism that explains the high incidence of silicon cratering when thermosonic gold ball bonds are sheared from aluminum metallized pads over silicon and SiO/sub 2/ is proposed. The mechanism is based on the transmission of energy from the ball shear ram through the rigid intermetallic weld to the underlying dielectric. The concentration of this transmitted energy in the form of stress concentrators was estimated, using finite-element modeling, to be highly dependent on ball and weld geometry. This failure mode does not require that the substrate be cracked initially through the use of improper bonding conditions, as cratering was observed to occur even though the range of bonding parameters used in this study produced no visible damage to the underlying dielectric material. The mechanism may be partly responsible for shear-induced cratering in plastic-encapsulated packages. Recommendations are made regarding steps that can be taken to reduce this effect by altering bonding parameters, pad metal thickness, and cure schedule. >

A comparison of copper and gold wire bonding on integrated circuit devices

A comparative approach was used to develop new copper wire bond technology using the current standard production gold wire process as a baseline. Characterizations were made in the areas of assembly processes and material selection, electrical and thermal performance, intermetallic formation on Al and Al alloy bond pads, and reliability testing. It was demonstrated that copper wire bond strength tested with wire-pull and ball-shear methods can be maintained at higher levels than comparable gold wire bonds. Die shear strengths were degraded by temperature cycling, but not by high-temperature storage. AC/DC parameter characterizations across temperature and power supply exhibited identical performances on copper and gold devices. Input impedance, capacitance, and ESD (electrostatic discharge) showed no deviations between Au and Cu wire bonded devices selected for this investigation. The lower resistivity of Cu wire offers the potential for increased device power ratings. The thermal transient response showed negligible differences between Au and Cu wire bonded devices. The difference in intermetallic growth rates between Au and Cu wire processed devices suggest that Cu wire bonded devices will have greater reliability than Au wire bonded devices. The reliability data indicate that copper wire bonding is at least equal to conventional gold wire bonding. It is concluded that a copper ball bond assembly process can be developed for mass production which will equal and potentially surpass the performance and reliability of the present gold ball bond assembly process. >

Correlation between electrical resistance and microstructure in gold wirebonds on aluminum films

Gold ball bonds attached to either pure Al films or Al films with Cu and Si additions were annealed at temperatures in the range 77-277 degrees C for periods of up to 3000 h. Electrical resistance of the bonds was measured to within +or-1 m Omega using a manual four-probe arrangement with an applied current of up to 100 mA. Nonlinear multiple regression analysis of the data produced an empirical model for the resistance increase up to 8 m Omega . The resistance increases are related to the intermetallic phases and void configurations observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improving thermosonic gold ball bond reliability : Tom D. Hund and Paul V. Plunkett. IEEE Trans. Compom. Hybrids mfg Technol.CHMT-8 (4), 446 (1985)

Improving thermosonic gold ball bond reliability : Tom D. Hund and Paul V. Plunkett. IEEE Trans. Compom. Hybrids mfg Technol.CHMT-8 (4), 446 (1985)

A study of gold ball bond intermetallic formation in PEDs using infra-red microscopy : P. K. Footner, B. P. Richards, C. E. Stephens and C. T. Amos. 24 a. Proc. IEEE Reliab. Phys. Symp., 102 (1986)

A study of gold ball bond intermetallic formation in PEDs using infra-red microscopy : P. K. Footner, B. P. Richards, C. E. Stephens and C. T. Amos. 24 a. Proc. IEEE Reliab. Phys. Symp., 102 (1986)

Experimental focal cerebral ischaemia in rabbits

A highly reproducible form of experimental embolization of the intracranial arteries is presented in rabbits. The injection of a silver or gold ball into the internal carotid artery caused occlusion predominantly of the middle cerebral artery and/or its branches. At the moment when embolization took place, the characteristic signs of acute cerebral ischaemia occurred in the electroencephalogram, local cerebral blood flow and steady (DC) potentials. Several hours after the ball had been injected the extent of the focal lesions became recognizable on sections stained for myelin. The procedure is simple, rapid, inexpensive and practically always successful. The extent of the lesion may be influenced by the change of both the ball size and the posture of animals. Moreover, the site of occlusion is easily discernible both on radiographs and to the naked eye.

Gold-Aluminum Intermetallics: Ball Bond Shear Testing and Thin Film Reaction Couples

The gold-aluminum intermetallic phases are known to contribute to the long term degradation of gold wire ball bonds to aluminum metallization on semiconductor devices. The properties of these intermetallics were investigated through two techniques: 1) ball bond shear testing and 2) preparation of known intermetallic compositions by using thin film Au-Al diffusion couples. The influence of thermal aging on gold ball bonds attached to aluminum metallization (on both Si and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) was determined through ball shear measurements. The strength of gold wire bonds made to films of Au-Al intermetallics was similarly measured. Failure mode analyses of the sheared bonds for the various systems examined are presented. The effect of a nondestructive ball shear test on the ultimate ball shear strength is given. Ultraviolet (UV)-ozone cleaning of the aluminum prior to gold wire bonding is discussed in light of Auger spectroscopy of the aluminum oxide formed on the surface. The effect of shearing direction relative to the direction of the ultrasonic scrubbing was also examined.

A New Failure Mechanism: Al-Si Bond Pad Whisker Growth During Life Test

The results are presented of a study conducted to determine reasons for and kinetics of the growth of thin aluminum whiskers from the bond pads of semiconductors. These whiskers were found to grow to lengths of up to 200 µm from thin-film aluminumsilicon on N-type silicon gate metal-oxide semiconductors (NMOS). Whisker growth was found to be due to the compressive stress generated in the metal during wire bonding. The problem is complicated by the presence of silicon grains in the Al-Si film and was found only on parts using gold ball bonds. The growth rate is temperature dependent with a thermal activation energy of 0.7 eV. Copper doping of the metallization as well as the use of aluminum ultrasonically bonded wires were both found to effectively prevent whisker growth.

A Gaussian Small Particle Population is Transformed by Pt-C Replication into Distributions of Metal Cap Widths and Shadow Widths which Empirically Fit a Log-Normal Function

The investigation of biological membranes would be greatly facilitated if the particle shadow widths (PSW) or particle cap width (PCW) distributions on freeze-fractured or freeze-etched membranes could be related to actual particle size and size diversity. By establishing how a gaussian population of small particles is transformed into its Pt-C PCW and its Pt-C particle shadow width distributions (PSWD), it may be possible to solve this problem.The negatively stained lac repressor (1% uranyl acetate, pH 4.8) which is roughly a gaussian population of diameters (fig. la) was used to investigate the distribution shape of Pt-C PCW's. Gold balls were only used to investigate the distribution shape of PSW's because they did not generally form a Pt-C metal cap (1,2). The preparation method for gold ball calibration grids has been reported (1,2). The Pt-C shadowing experiments (45° angle) were performed on a Balzer's model 360M freezing microtome at -97°C to -94°C in a 10-6 torr vacuum. An EKV 552 Pt-C electron beam gun was either degassed for 19 sec (film I) or for 120 sec (film II) at a current setting of 5 on the EVM 052 control unit.

The Extent of Platinum-Carbon Electron Beam Gun Degassing Before Replication Can Change the Size and Frequency of Replicated Small Particles

The freeze-fracture of cellular membranes generally reveals particles of different sizes distributed on a membrane fracture face. These views of the membrane are generally characterized by the frequency of particles per area and a particle shadow width distribution with its mean. It is generally assumed that these particle size and frequency parameters can be influenced by the replica film thickness and the shadowing angle. It is not known whether the extent of Pt-C electron beam gun degassing prior to the replication step can change the shadow width distribution means of spherical gold particles, and their percent representation following replication.Two experiments were performed in a Balzer's model 360M freezing microtome (10-6 torr) in which the EKV 552 Pt-C electron beam gun was degassed for 19 sec. (film I) and for 120 sec. (film II) at a current setting of 5 on the EVM 052 control unit. The gold ball calibration grids (2) were cooled to -96°C and covered with the knife arm (-196°C) during degassing.

High-Reliability Thermocompression Bonding for Hybrid Applications

The problem of producing reliable thennocomprassion gold ball bonds to aluminum metallization has been discussed by many authors. In most of these discussions, little information is provided to relate bond reliability to process parameters-cleanliness and bonder settings. The influence of bond and capillary temperatures upon bond integrity is discussed. The use of beryllia capillaries to achieve the high capillary temperatures achievable with pulse tip bonding without sacrificing production throughput is discussed. An accelerated life test for ascertaining bond reliability is discussed and shown to be an effective tool for process prove-in. Finally, a bonding technique is discussed that not only meets the requirements of MIL STD 883A, but also will withstand temperature stresses equivalent to 300°C storage for 4 h, 2000 h of accelerated operating life, and 1300 temperature cycles.

Nondestructive Bond Pull in High-Reliability Applications

The problem of producing reliable thermocompression gold ball bonds to aluminum metallization has been discussed by many authors. In most of these discussions, little information is provided to relate bond reliability to process parameters-cleanliness and bonder settings. The influence of bond and capillary temperatures upon bond integrity is discussed. The use of beryllia capillaries to achieve the high capillary temperatures achievable with pulse tip bonding without sacrificing production throughput is discussed. An accelerated life test for ascertaining bond reliability is discussed and shown to be an effective tool for process prove-in. Finally, a bonding technique is discussed that not only meets the requirements of MIL STD 883A, but also will withstand temperature stresses equivalent to 300°C storage for 4 h, 2000 h of accelerated operating life, and 1300 temperature cycles.

Kinetics of Thermocompression Bonding to Organic Contaminated Gold Surfaces

The kinetics of thermocompression gold ball bonding were studied for gold metallization contaminated with organic films. The contaminants studied were residual photoresist and atmospheric contamination. For gold metallization contaminated with organic films, thermo-compression gold bonding is a two-stage process. The first stage occurs within a fraction of a second and results from the mechanical disruption of barrier films by shear displacements at the faying surface. Bonding during this initial stage is a strong function of the interface temperature, the bonding force, and the contaminant films. The second stage involves growth of the metal-metal interfaces by a sintering phenomenon. Growth of bonds by sintering also occurs in the absence of external loads though at a decreased rate. Analysis of the rate data leads to the conclusion that the growth mechanism follows a parabolic rate law and, in the absence of external loads, exhibits an activation energy of approximately 11 kcal/mole. Under high external loads, the rate of second-stage growth exhibited little temperature dependence, indicative of a stress-assisted process. Bond growth rates for the atmospherically contaminated metallization were an order of magnitude higher than that for the photoresist contaminated samples.