Accepted Manuscripts

Review Article  
Yuyan Gao and Huanyu Cheng
J. Electron. Packag   doi: 10.1115/1.4036238
Specific function or application in electronics often requires assembly of heterogeneous materials in a single system. Schemes to achieve such goals are of critical importance for applications ranging from the study in basic cell biology to multifunctional electronics for diagnostics/therapeutics. In this review article, we will first briefly introduce a few assembly techniques such as micro-robotic assembly, guided self-assembly, additive manufacturing, and transfer printing. Among various heterogeneous assembly techniques, transfer printing represents a simple yet versatile tool to integrate vastly different materials or structures in a single system. By utilizing such technique, traditionally challenging tasks have been enabled and they include novel experimental platforms for study of 2D materials and cells, bio-integrated electronics such as stretchable and biodegradable devices, and 3D assembly with advanced materials such as semiconductors.
TOPICS: Manufacturing, Biomimetics, Electronics, Biology, Printing, Self-assembly, Advanced materials, Robotics, Semiconductors (Materials), Additive manufacturing, Biodegradation
Review Article  
Kaysar Rahim and Ahsan Mian
J. Electron. Packag   doi: 10.1115/1.4036239
The packaging of electronic and MEMS (micro-electromechanical systems) devices is an important part of the overall manufacturing process as it ensures mechanical robustness as well as required electrical/electromechanical functionalities. The packaging integration process involves the selection of packaging materials and technology, process design, fabrication, and testing. As the demand of functionalities of an electronic or MEMS device is increasing every passing year, chip size is getting larger and is occupying the majority of space within a package. This requires innovative packaging technologies so that integration can be done with less thermal/mechanical effect on the nearby components. Laser processing technologies for electronic and MEMS packaging have potential to obviate some of the difficulties associated with traditional packaging technologies and can become an attractive alternative for small-scale integration of components. As laser processing involves very fast localized and heating and cooling, the laser can be focused at micrometer scale to perform various packaging processes such as dicing, joining, patterning, etc. at the microscale with minimal or no thermal effect on surrounding material or structure. As such, various laser processing technologies are currently being explored by various researchers and also being utilized by electronic and MEMS packaging industries. This paper reviews the current and future trend of electronic and MEMS packaging and their manufacturing processes. Emphasis is given to the laser processing techniques that have the potential to revolutionize the future manufacturing of electronic and MEMS packages.
TOPICS: Lasers, MEMS packaging, Packaging, Manufacturing, Microelectromechanical systems, Microscale devices, Testing, Process design, Robustness, Temperature effects, Joining, Mechanical properties, Heating and cooling, MEMS packages
Jingshi Meng and Abhijit Dasgupta
J. Electron. Packag   doi: 10.1115/1.4036187
Portable electronic devices are commonly exposed to shock and impact loading due to accidental drops. After external impact, internal collisions (termed “secondary impacts” in this study) between vibrating adjacent subassemblies of a product may occur if design guidelines fail to prevent such events. Secondary impacts can result in short acceleration pulses with much higher amplitudes and higher frequencies than those in conventional board level drop tests. Thus such pulses are likely to excite the high frequency resonances of printed wiring boards (PWBs) (including through-thickness ‘breathing’ modes) and also of miniature structures in assembled surface mount technology (SMT) components. Such resonant effects have a strong potential to damage the component, and therefore should be avoided. When the resonant frequency of a miniature structure (e.g. elements of a SMT MEMS component) in an SMT assembly is close to a natural frequency of the PWB, an amplified response is expected in the miniature structure. Components which are regarded as reliable under conventional qualification test methods, may still pose a failure risk when secondary impact is considered. This paper is the second part of a two-part series exploring the effect of secondary impacts in a printed wiring assembly (PWA). The first paper is this series focused on the ‘breathing’ mode of vibration generated in a PWB under secondary impact and this paper focuses on analyzing the effect of such ‘breathing’ modes on typical failure modes with different resonant frequencies in SMT applications. The results demonstrate distinctly different sensitivity of each failure mode to the impacts.
TOPICS: Failure mechanisms, Electrical wires, Surface mount components, Resonance, Printed circuit boards, Manufacturing, Collisions (Physics), Shock (Mechanics), Microelectromechanical systems, Design, Surface mount technology, Vibration, Failure, Risk, Damage
Thong Kok Law, Fannon Lim, Yun Li, XuePeng Puan, G.K.E. Sng and Jin Wah Ronnie Teo
J. Electron. Packag   doi: 10.1115/1.4036066
The phosphor and die bonding configuration affect the optical efficiency and thermal performance in phosphor-coated white LEDs. In this paper, light emission studies reveal that the chromaticity shift and light extraction losses depend on the uniformity of phosphor particles deposited over the LED surface. A non-uniform and sparse phosphor layer affects the correlated color temperature (CCT) and the spectral Y-B ratio due to the disproportionate contribution of light emission between the LED device and the phosphor layer. Furthermore, the Y-B ratio was observed to reduce with temperature due to higher Stoke's energy and light extraction losses in the phosphor layer. As a result, the Y-B ratio exhibits an inverse relationship with the package's thermal resistance as a function of temperature. On the other hand, the thermal performance of a LED package is dependent on the die-bonding configurations (conventional and flip-chip). Due to the improved heat dissipation capabilities in flip-chip bonding, the temperature rise and thermal resistance of the package was observed to reduce with temperature. By alleviating the heat accumulation in the package, more stable colorimetric properties such as CCT and Y-B ratio can be achieved.
TOPICS: Light-emitting diodes, Packaging, Phosphors, Temperature, Bonding, Thermal resistance, Heat, Light emission, Flip-chip, Particulate matter, Energy dissipation
Srivathsan Sudhakar and Justin A. Weibel
J. Electron. Packag   doi: 10.1115/1.4036065
For thermal management architectures wherein the heat sink is embedded close to a dynamic heat source, non-uniformities may propagate through the heat sink base to the coolant. Available transient models predict the effective heat spreading resistance to calculate chip temperature rise, or simplify to a representative axisymmetric geometry. The coolant-side temperature response is seldom considered, despite the potential influence on flow distribution and stability in two-phase microchannel heat sinks. This study solves three-dimensional transient heat conduction in a Cartesian chip-on-substrate geometry to predict spatial and temporal variations of temperature on the coolant side. The solution for the unit step response of the three-dimensional system is extended to any arbitrary temporal heat input using Duhamel's method. For time-periodic heat inputs, the steady-periodic solution is calculated using the method of complex temperature. As an example case, the solution of the coolant-side temperature response in the presence of different transient heat inputs from multiple heat sources is demonstrated. To represent a case where the thermal spreading from a heat source is localized, the problem is simplified to a single heat source at the center of the domain. Metrics are developed to quantify the degree of spatial and temporal non-uniformity in the coolant-side temperature profiles. These non-uniformities are mapped as a function of nondimensional geometric parameters and boundary conditions. Several case studies are presented to demonstrate the utility of such maps.
TOPICS: Heat, Heat sinks, Transient analysis, Temperature, Coolants, Transients (Dynamics), Geometry, Transient heat transfer, Microchannels, Architecture, Boundary-value problems, Temperature profiles, Thermal management, Stability, Flow (Dynamics)
Joel Thambi, Andreas Schiessl, Manuela Waltz, Klaus-Dieter Lang and Ulrich Tetzlaff
J. Electron. Packag   doi: 10.1115/1.4035850
This paper, explicitly establishes a modified creep model of a Sn3.8Ag0.7Cu alloy using a physical based micro-mechanical modelling technique. Through experimentation and reformulation steady-state creep behavior, is analyzed with minimum strain rates for different temperatures 35°C, 80°C, and 125°C. The new modified physical creep model is proposed, by understanding the respective precipitate strengthened deformation mechanism, seeing the dependency of the activation energy over the temperature along with stress and fi-nally by integrating the subgrain size dependency λss. The new model is found to accurately modelling the creep behavior of Lead free solder alloy by combining the physical state variables. The features of the creep model can be explored further by changing the physical variable such as subgrain size to establish a struc-ture - property relationship for a better solder joint reliability performance.
TOPICS: Creep, Alloys, Modeling, Lead-free solders, Temperature, Reliability, Stress, Solder joints, Steady state, Deformation

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