Search

Automatic speech recognition (ASR) technology has been used by researchers to develop voice-controlled robots. However, the usual pattern is to develop an ASR interface that works specifically with one particular robot. Generalized ASRs, ones that can communicate with multiple robots, are needed. A generalized ASR allows an operator to control several robots that are operated by different programming languages at the same time via a single interface. This paper describes the development and an initial user study of a generalized ASR interface using a commercially available ASR software. The user study provided initial validation of the interface's functionality using a variety of commands. Results indicated a reasonably high input flexibility; the interface successfully recognized 85% of 1200 spoken commands. It also demonstrated output flexibility; the generalized ASR fed the robot a sequence of keystrokes that formed any syntax required to trigger its task programs. Implications for human-robot interaction are discussed.

This paper will show the benefits of the latest stretchable inks and z-axis adhesives for flexible hybrid electronics (FHE) applications. These stretchable inks and z-axis adhesives will be used to build a simple multilayer flashing LED assembled on a thermoplastic urethane (TPU) substrate using standard electronic packaging methods and evaluated for tensile, strain testing, and effects of humidity and temperature.The results from the previous study of single layer silver based and carbon-based structures showed materials remain conductive over large strain however resistance did change for elongation testing and strain testing. Silver based materials had a greater resistance to change compared to carbon-based materials. However, the later had a better resistance recovery.For humidity and temperature evaluations, the silver based single layer samples showed small decrease in resistance under temperature and humidity while the carbon based single layer showed small decrease during the initial twenty-four hours then remained constant for the remainder of the test.Same tests profiles were carried on three assembled multilayer LED flashing circuit with three configurations: non-encapsulated SMD components, encapsulated with old formulation (encapsulant A), and with a new formulation (encapsulant B). Results show that fully encapsulated samples with encapsulant B have the highest resistance to mechanical and environmental stresses.

The continued desire for an alternative to lead-based solder materials for electrical interconnections has led to significant research interest in Anisotropic Conductive Adhesives (ACAs). These create bonds using a combination of metal particles and epoxies to replace solder. The novel ACA discussed in this paper allows for bonds to be created through aligning columns of conductive particles along the Z-axis. These columns are formed by the application of a magnetic field, during the curing process. The benefit of this novel ACA is that it does not require precise printing of the adhesive on pads and also enables the mass curing without creating shorts in the circuitry. The novel ACA’s applicability for PCB-level assembly has been successfully demonstrated by RIT. The research at RIT has also characterized the base material properties, analyzed the effect of various process parameters, identified failures, and investigated the ACA’s long-term reliability for surface mount PCB assembly. Reliability testing included an investigation of the assembly performance in temperature and humidity aging, thermal aging, air-to-air thermal cycling, and drop testing conditions. For example, it has been shown that by modifying the filler particle size and coating, reliability of >1500 hours in high temperature, high humidity aging (HTHH), and 100 hours in highly accelerated stress testing (HAST) can be successfully achieved. This paper highlights research comparing the shear loading performance of the novel ACA to that of tin-lead and lead free solders. Samples assembled with the adhesive and the solders were subjected to multiple tin-lead and lead free reflow cycles. The primary objective was to understand the deterioration in shear loading as influenced by multiple reflow cycles. Published research materials have shown the influence of the change in solder joint performance with multiple reflows due to the increase in intermetallic thickness. The results of a DOE study show the influence of the various factors and levels. Shear stress calculations indicate higher stress experienced by the adhesive joints as compared to the solder joints due to the spreading of the solder during wetting. Empirical relationships will be derived from the experimental data to help determine the required contact area for a given level of shear loading. The experimental results also reveal the rapid decrease in Shear stress between the first and second reflow and the slow decline in strength up to five reflows. Findings from this work will be used to assess the use and reliability of this adhesive for attaching the top component of Package-on-Package (PoP) 3D stacked components, in thermal cycling, HAST and HTHH environments.

Distance learning has been one vehicle of course delivery at the Rochester Institute of Technology since the early 1990s. Building on the authors' experience in teaching completely online and blended (partly on-campus and partly online) courses to both undergraduate and graduate students, in diverse areas of computing, engineering, and technology, this paper explores issues in delivering online classes in these disciplines. One particular focus is on conveying the traditional in-class laboratory experience to a similar one in the online world while another focus is to leverage the modalities available in online to create newer and richer experiences for students and instructor. The paper presents the challenges and pitfalls in totally asynchronous learning, from assessment to assignments, from lectures to labs, and from participation to plagiarism. For each challenge, the authors provide examples of practices that succeeded, building on experience with those that did not. To place this work in perspective, the paper also examines related work in online computing and engineering education.

In recent years, the electronics industry has been focused on product miniaturization and RoHS compliance, through new component and PCB assembly technologies. In portable consumer products, while chip stacking via the system in package (SiP) approach is becoming quite popular, the use of conventional packaging techniques is complicated, and results in large parasitic inductances. The need for planarity, additional processing steps, and high temperature processing, make bumping and flip chip bonding a less than ideal solution. These challenges and the need to eliminate lead-based solders and halogen containing substrate materials have renewed the industry's interest in exploring newer assembly methods at both the component packaging and lead-free PCB assembly levels, especially by using conductive adhesives. Conductive adhesives can be typically processed at a relatively low temperature which is important for thermally sensitive components. This paper will provide a summary of the research using a novel ZTACH™ anisotropic conductive adhesive (ACA) for component level and lead free Printed Circuit Board (PCB) level packaging.

Quad Flatpack No lead (QFN) packages have become a popular choice in electronics packaging due to its small form factor. They are also gaining rapid industry acceptance because of its excellent thermal and electrical performance. The bottom side of the QFN package has a large thermal pad. This exposed die attach pad effectively conducts heat to the PCB and also provides a stable ground connection. Effective soldering of this surface to the pad on the PCB is required for good thermal dissipation and component functionality. The exposed thermal pad presents various challenges during the surface mount assembly process. One major challenge is solder void formation. Voids are primarily formed due to the entrapment of volatiles in flux outgassing during the reflow process. The primary objective of this study is to determine optimal parameters to minimize void formation in QFN packages (QFN16, QFN20, QFN28, QFN32 and QFN44), specifically the reflow profile, lead-free solder paste and stencil aperture opening for the thermal pad. A systematic Design of Experiments (DOE) based approach was used to arrive at conclusions, using the ratio of void volume on the thermal pad to the actual volume of solder paste printed, as the response variable. A theoretical thermal resistance response variable was also modeled to analyze the DOE parameters and the conclusions were similar to the void model. Various graphs are presented to understand the impact of different parameters. Interaction graphs are used to determine optimal settings for each parameter. A regression equation for relationship between the factors and the void volume is identified to predict void volumes for any given component, paste volume and paste transfer efficiency.Copyright © 2010 by ASME

A wide array of lead-free alloys is available in the market and distinguishing one over the other is not an easy task. Several factors have to be considered before making a choice. Reliability under both thermal and mechanical conditions is one such factor. This experimental research aims at making a comparison of the different lead-free solder ball alloys for area array and advanced packages, assembled using lead-free solder paste. Package reliability will be compared for No-underfill, Corner-underfill and Full-underfill. Assembly reliability was evaluated by subjecting the assemblies to 30 mechanical drops in the as-assembled(AS) condition and after 200 and 500 thermal shock cycles (TS). The scope of this paper is limited to the performance evaluation for area array packages (UCSP, PBGA676, PBGA1156, PoP, CVBGA). Solder ball alloy for the area array packages include SAC305, SAC405, SAC105 and SnAg. The solder paste used for the assembly is SAC305 with Type 3 solder particle size. Three different PCB surface finishes, electroless nickel immersion gold (ENIG), SnPb hot air solder level (HASL), and immersion silver (ImAg) are used. Different solder ball alloys and surface finish combinations will provide data to compare intermetallic thickness. Assembly reliability was evaluated by subjecting the assemblies to 30 mechanical drops in the as-assembled condition and after 200 and 500 thermal shock cycles. After each drop the components were checked for the continuity of the total daisy chain. The number of drops for the first failure was used in analyzing the performance of the components for various combinations. Since each component had many independent daisy chains, the failure of the individual daisy chains was later used in determining the location of the failure and how it progressed. Test results gathered for no-underfill, corner-underfill and full-underfill assemblies indicate SnAg alloys for the solder balls to be performing better than the SAC305 and SAC405 alloys for PBGA676, irrespective of the PCB pad surface finish. The location on the PCB could have had an influence on these packages. An improvement in drops to failure was also observed for some packages with corner-underfill. But with full-underfill the improvement was observed for all packages. It was also observed that UCSP failed to withstand 500 thermal shock cycles for no-underfill and corner-underfill assemblies. But the package was able to withstand 500 cycles of thermal shock for full-underfill assemblies. Solder joint analysis reveals pad cratering and crack formation to be the root cause for failure. These packages were also cross-sectioned in order to record the changes in intermetallic thickness. This paper will provide a detailed analysis of the findings.

Quad Flatpack No lead (QFN) packages have become a popular choice in electronics packaging due to its small form factor. They are also gaining rapid industry acceptance because of its excellent thermal and electrical performance. The bottom side of the QFN package has a large thermal pad. This exposed die attach pad effectively conducts heat to the PCB and also provides a stable ground connection. Effective soldering of this surface to the pad on the PCB is required for good thermal dissipation and component functionality. The exposed thermal pad presents various challenges during the surface mount assembly process. One major challenge is solder void formation. Voids are primarily formed due to the entrapment of volatiles in flux outgassing during the reflow process. The primary objective of this study is to determine optimal parameters to minimize void formation in QFN packages (QFN16 and QFN20), specifically the reflow profile, leadfree solder paste and stencil aperture opening for the thermal pad. A systematic DOE based approach was used to arrive at conclusions, using the ratio of void volume on the thermal pad to the actual volume of solder paste printed as the response variable. Various graphs are presented to understand the impact of different parameters. Interaction graphs were used to determine optimal settings for each parameter.

Quad Flatpack No lead (QFN) packages have become a popular choice in electronics packaging due to its small form factor. They are also gaining rapid industry acceptance because of its excellent thermal and electrical performance. The bottom side of the QFN package has a large thermal pad. This exposed die attach pad effectively conducts heat to the PCB and also provides a stable ground connection. Effective soldering of this surface to the pad on the PCB is required for good thermal dissipation and component functionality. The exposed thermal pad presents various challenges during the surface mount assembly process. One major challenge is solder void formation. Voids are primarily formed due to the entrapment of volatiles in flux outgassing during the reflow process. The primary objective of this study is to determine optimal parameters to minimize void formation in QFN packages (QFN16, QFN20, QFN28 and QFN32), specifically the reflow profile, lead-free solder paste and stencil aperture opening for the thermal pad. A systematic DOE based approach was used to arrive at conclusions, using the ratio of void volume on the thermal pad to the actual volume of solder paste printed as the response variable. Various graphs are presented to understand the impact of different parameters. Interaction graphs are used to determine optimal settings for each parameter.Copyright © 2009 by ASME

With lead-free implementation it is important to examine the behaviour of the solder joint at the component level and at the board level. Assembly related issues along with component reliability are the main focus of this experimental research. This experimental study aims to evaluate the mechanical integrity of solder joints comprising of both lead-free and SnPb alloys. Lead-free and SnPb solder pastes were used to assemble the components. This will allow us to check the forward and the backward compatibility of the solder alloys. The test vehicle considered for this study contained a variety of components such as ultra chip scale package (UCSP192), package on package (PoP), plastic ball grid array (PBGA-676 & 1156), very thin chip array BGA (CVBGA432), thin small outline package (TSOP-40 & 48), dual row micro-lead frame (DRMLF), micro-lead frame (MLF-36 & 72), and chip resistors (0201, 0402, 0603). The scope of this paper is limited to the performance evaluation for area array packages only. Solder ball alloy for the area array packages included SAC 305, SAC405, SAC105, SnAg and SnPb. Three different PCB surface finishes, electroless nickel immersion gold (ENIG), SnPb hot air solder level (HASL), and immersion silver (ImAg) were used. Different solder ball alloys and surface finish combinations provided good comparison data for investigating the assembly performance. The PCB assemblies were subjected to mechanical shock test in the as-soldered condition and also after 200 and 500 thermal shock cycles at −55 to 125°C. For the mechanical shock test, the assemblies were subjected to 30 drops from a height of 3 ft, generating an average G force of 485N. After each drop the components were checked for the continuity of the total daisy chain. The number of drops for the first failure was used in analyzing the performance of the components for various combinations. Since each component had many independent daisy chains, the failure of the individual daisy chains was later used in determining the location of the failure and how it progressed. Two sets of test vehicles were assembled. One set comprised of components with lead-free solder balls of different composition (SAC305, SAC405, SAC105, SnAg) and the other set comprised of components with lead-free solder balls and SnPb solder balls (SAC305, SAC405, SnPb). This mix of alloy composition provided adequate data for comparison. It was critical to optimize the process in order to enable the melting of the mix of alloys. The area array package performance was evaluated when assembled with lead-free and SnPb solder paste. Some of the assemblies were cross-sectioned after the tests and the microstructure of the solder joint was analyzed to study the possible cause for assembly failure.

Quality management (QM), which includes quality monitoring, data analysis and data reporting, requires continuous inspection of product quality, process quality and equipment/tool condition. Product quality monitoring inspects the products after they have been manufactured or assembled. This does not provide a real-time indication of the process that is making the product. Hence, it becomes more of a non-value added task to separate the good from the bad. On the other hand, process quality or equipment/tool condition monitoring provides value-added real-time feedback of the drift in the process. This information will be useful for adaptive control of the process and equipment, to produce good parts and assemblies. With the advent of the web, and its use to control various aspects of manufacturing and assembly, real-time web-based Automatic Inspection (AI) and QM have become very attractive and viable. Web-based AI and QM will enable effective real-time integration of shop-floor dynamics into the Manufacturing Execution Systems (MES) and the Enterprise Resource Planning Systems (ERPS). This will provide effective monitoring and adaptive control of the manufacturing enterprise and its supply chain.

The novel Anisotropic Conductive Adhesive (ACA) investigated in this research uses a magnetic field to align the conductive particles in the Z-axis direction, during cure, thereby eliminating the need for pressure and the requirement to capture a monolayer of conductive particles. The formation of conductive columns within the adhesive matrix, during cure, provides a very high insulation resistance between adjacent conductors and also eliminates the need for precise printing or dispensing of adhesives onto individual fine pitch pads. The novel ACA can also be mass cured, eliminating the need for sequential component assembly. The formation of columns also alleviates the problems associated with coplanarity errors and varying lead/bump shapes in forming reliable interconnections using traditional AC As. This research incorporated a variety of components, leaded, leadless and bumped, standard, fine and ultrafine pitch, coarse and fine particle filler formulations, different stencil thicknesses, different cure temperatures and times, and different magnetic flux densities. The print process was performed manually using metal stencils of different thicknesses and metal squeegee blades. The findings from this study, including drop tests of 'as assembled' and aged samples (100 hours of thermal and T&H aging) are provided. The filler particle size played a critical role in determining the continuity and the contact resistance of the adhesive joint. Standard pitch devices provided good continuity and contact resistance when assembled with larger diameter filler particles. Fine pitch devices required smaller diameter filler particles. Stencil thickness was found to be a statistically significant factor in determining the contact resistance of the adhesive joint, while magnetic flux and cure temperature were not significant statistically. A magnetic flux of 2000 Gauss and a cure schedule of 150degC for 7 minutes were found to work effectively for different material formulations. A thinner stencil (100 mum - 4 mils) was required to obtain continuity when assembling fine pitch devices whereas a thicker stencil (>200 mum - 8 mils) was required when assembling standard pitch devices. Thicker stencil prints tend to misalign the fine pitch devices considerably after placement and cure. A thick adhesive print, with fine particle material formulation, and high magnetic flux density resulted in the filler particles growing as dendrites past the surface of the adhesive. Vertical orientation for the assemblies during drop test, from a height of 900mm (36 inches), was found to be more reliable when compared to the horizontal orientation, in both the 'as assembled' and thermally aged conditions. The daisy chains for all of the components survived 30 drops in the vertical orientation. MicroLeadframe (MLF) devices survived 30 drops in both the horizontal and vertical orientations. These devices showed the best performance during drop testing. None of the assemblies survived the T&H aging for 100 hours, to carry out the drop tests.

The primary objective of this experimental research is to understand the common issues faced in a manufacturing environment that assembles products containing a variety of fine-pitch devices. The testing phase of the research, relates to characterizing the thermo-mechanical integrity of surface mount mixed (Sn-Pb & lead-free) assembly solder joints. The investigation involves both forward and backward compatibility in electronics assemblies on Pb-free PWB surface finishes. A full factorial design is used in the investigation, with 3 factors — solder paste, component finish and PWB surface finish. Eutectic Sn-Pb paste (63–37% wt) and SAC305 (Sn 3.0%Ag0.5%Cu) paste are used as Pb-containing and Pb-free levels respectively. For component finish metallization, Sn-Pb termination finish/bump composition is used for Pb-containing level while Sn termination/SAC 405 bump composition represents the Pb-free level. Immersion Silver (ImAg) and Electroless Nickel Immersion Gold (ENIG) surface finish on printed wiring board (PWB) is used for testing and analysis. The testing was aimed at providing results for a wide variety of fine-pitch components commonly used in surface mount solder assemblies. Hence, a PWB containing flip chip (0.4mm pitch), Ultra chip scale package (UCSP), micro-lead frame (MLF) or quad flat pack no-lead (QFN), thin small outline package (TSOP −0.5 mm pitch) and plastic ball grid array (PBGA −1156 I/O and 256 I/O −1 mm pitch) devices was designed and used for testing. The test vehicle also includes resistors (0201, 0402 & 0603). The stencil thickness and openings were selected to accommodate both the large PBGA (1156 I/O) and finer pitch components. The reflow profile was designed taking into account the component maximum temperature exposure limitations, due to non-uniformity in heating, determined from thermocouples during initial assembly. Lessons learned from the design, reflow process optimization and manufacturing are presented in this paper. The solder joints were subjected to isothermal aging followed by mechanical shock test, attempting to establish a relationship between the intermetallic growth at the solder/PWB interface and the mechanical integrity of the solder joint. The compounding of test, unlike singular test methods, provides a more realistic estimate of the reliability and life of the joint in the field. The assemblies were cross-sectioned after the tests and the microstructure of the solder joints will be analyzed to study the intermetallic growth upon isothermal aging.

The need to eliminate lead-based materials as a means of interconnection has renewed the electronics industry’s interest in using conductive adhesives for component attach, especially Anisotropic Conductive Adhesives (ACA). Typical ACAs require the application of pressure during the curing process, to establish the electrical connection and also to capture a monolayer of conductive particles between the mating surfaces. The novel ACA discussed in this paper uses a magnetic field to align the particles in the Z-axis direction during curing and eliminates the need for pressure. The application of the magnetic field allows for the formation of conductive chains between the mating surfaces, thereby eliminating lateral conductivity. This uniqueness of the novel ACA also accommodates for any coplanarity error and the formation of effective Z-axis conductivity, with a variety of lead and bump shapes. The novel ACA also enables mass curing of the adhesive, eliminating the need for sequential assembly. As part of the study presented in this paper, the conductive chains were modeled as series and parallel resistor networks in an insulating adhesive matrix. The number of particles in the chain and hence the number of interfaces between the particles is found to influence the initial contact resistance of the joints. The interfacial resistance is derived from the experimental run. Area array packages with and without bumps, reveal varying contact resistances as indicated by the model and experiment. This paper will present a model for the conductive chain formation in the novel ACA, and discuss the experimental results obtained to verify the joint contact resistance.

This paper presents the test results and comparative literature data on the influence of a few key manufacturing parameters and defects associated with the 0201 components using lead-free and tin-lead solder alloys. A large number of test vehicles assembled with 0201 components were subjected to isothermal aging at 150/spl deg/C and thermal cycling in the range of -55/spl deg/C to 100/spl deg/C in order to establish their reliability. The shear tests were carried out at various aging intervals up to 500 hours to determine the effects of aging damage on the solder joint strength and this data are presented and compared to virgin assemblies. Weibull plots are given for reliability to establish solder joint aging behavior for the lead free assemblies compared to lead based solder as well as data correlation for various sets of data. Optical inspection photos taken during thermal cycling to establish damage progress, scanning electron microscopy (SEM) photos to reveal details of damage at 1500 cycles, and cross-sectional photomicrographs showing interconnect microstructural changes and intermetallic formation are also be presented.

The electronics industry, in recent years, has been focusing primarily on product miniaturization and lead-free assembly. The need for product miniaturization is due to the continuous demand for portable electronic products that are multifunctional, yet smaller, faster, cheaper, and lighter. This is forcing the industry to design and assemble products with miniature passive and active devices. These devices typically have fine pitch footprints that provide a very small surface area for attachment. The solder attach technique relies primarily on the formation of intermetallics between the mating metallic surfaces. With a reduction in the surface area of the pads, the ratio of intermetallic to solder is very high once the solder joint is formed. This could result in unreliable solder joints, due to the brittle nature of intermetallics. In addition, the need to eliminate lead-based materials as a means of interconnection has renewed the industry’s interest in exploring other means of assembling surface mount devices reliably. The use of a novel anisotropic conductive adhesive (ACA) as a means for assembling surface mount devices, the ACA’s performance characteristics, and preliminary research findings are discussed in this paper. Typically, ACAs require the application of pressure during the curing process to establish the electrical connection. The novel ACA uses a magnetic field to align the particles in the Z-axis direction and eliminates the need for pressure during curing. The formation of conductive columns within the polymer matrix provides a very high insulation resistance between adjacent conductors. The novel ACA also enables mass curing of the adhesive, eliminating the need for sequential assembly. The novel ACA was found to be very effective in providing the interconnection for surface mount technology (SMT) passives and leaded, bumped, or bumpless integrated circuit packages. The requirement for precise stencil printing was eliminated, as the application of magnetic field aligned the conductive columns in the Z-axis direction eliminating any lateral conductivity. The ability to mass cure the adhesive while applying the magnetic field reduced the assembly time considerably. Placement accuracy was still found to be very critical. Shear testing of adhesive joints after thermal aging showed significance past 500 h and after temperature–humidity aging showed significance within the first 100 h. I–V characteristics of the daisy chained ball grid array devices assembled with and without bumps revealed considerable difference in the breakdown current. The correlation between initial contact resistance of the daisy chain and the final breakdown current was also determined. Preliminary experiments and findings, discussed in this paper, show the viability of the ACA for mixed SMT assembly. Further experimentations will include in situ contact resistance measurements during thermal aging, temperature–humidity aging, drop testing and thermal shock.