Assembly Bonded at the Ends: Could Thinner and Longer Legs Result in a Lower Thermal Stress in a Thermoelectric Module Design?

2012 ◽  
Vol 79 (6) ◽  
Author(s):  
E. Suhir ◽  
A. Shakouri
Keyword(s):  
Thermal Stress ◽  
Stress Level ◽  
Thermoelectric Module ◽  
Interfacial Strength ◽  
Interfacial Stress ◽  
Electrical Performance ◽  
Shearing Stress ◽  
Interfacial Shearing Stress ◽  
Numerical Example ◽  
Module Design

An analytical (mathematical) thermal stress model has been developed for an electronic assembly comprised of identical components bonded at their end portions and subjected to different temperatures. The model is used to assess the effect of the size (dimension in the x-direction) and compliance of the bonded regions (legs) on the maximum interfacial shearing stress that is supposedly responsible for the mechanical robustness of the assembly. The numerical example is carried out for a simplified two-legged Bismuth-Telluride-Alloy (BTA)-based thermoelectric module (TEM) design. It has been determined that thinner (dimension in the horizontal, x-direction) and longer (dimension in the vertical, y-direction) bonds (legs) could result in a considerable relief in the interfacial stress. In the numerical example carried out for a 10 mm long (dimension in the x-direction) TEM assembly with two peripheral 1 mm thick (dimension in the x-direction) legs, the predicted maximum interfacial shearing stress is only about 40% of the maximum stress in the corresponding homogeneously bonded assembly, when the bond occupies the entire interface between the assembly components. It has been determined also that if thick-and-short legs are employed, the maximum interfacial shearing stress might not be very much different from the stress in a homogeneously bonded assembly, so that there is no need, as far as physical design and robustness of the assembly is concerned, to use a homogeneous bond or a multileg system. The application of such a system might be needed, however, for the satisfactory functional (thermo-electrical) performance of the device. In any event, it is imperative that sufficient bonding strength is assured in the assembly. If very thin legs are considered for lower stresses, the minimum acceptable size (real estate) of the interfaces (in the horizontal plane) should be experimentally determined (say, by shear-off testing) so that this strength is not compromised. On the other hand, owing to a lower stress level in an assembly with thin-and-long legs, assurance of its interfacial strength is less of a challenge than for an assembly with a homogeneous bond or with stiff thick-and-short legs. The obtained results could be used particularly for considering, based on the suggested predictive model, an alternative to the existing TEM designs, which are characterized by multiple big (thick-and-long) legs. In our novel design, fewer small (thin-and-short) legs could be employed, so that the size and thickness of the TEM is reduced for the acceptable stress level.

Predicted Thermal Stress in a Multileg Thermoelectric Module (TEM) Design

2013 ◽  
Vol 80 (2) ◽  
Author(s):  
E. Suhir ◽  
A. Shakouri
Keyword(s):  
Thermal Stress ◽  
Thermoelectric Material ◽  
Thermal Stresses ◽  
Thermoelectric Module ◽  
Vertical Direction ◽  
Interfacial Strength ◽  
Bonding System ◽  
Different Temperatures ◽  
Short And Long Term ◽  
Future Work

A physically meaningful analytical (mathematical) model is developed for the prediction of the interfacial shearing thermal stress in an assembly comprised of two identical components, which are subjected to different temperatures. The bonding system is comprised of a plurality of identical columnlike supports located at equal distances (spaces) from each other. The model is developed in application to a thermoelectric module (TEM) design where bonding is provided by multiple thermoelectric material supports (legs). We show that thinner (dimension in the horizontal direction) and longer (dimension in the vertical direction) TEM legs could result in a significant stress relief, and that such a relief could be achieved even if shorter legs are employed, as long as they are thin and the spacing between them is significant. It is imperative, of course, that if thin legs are employed for lower stresses, there is still enough interfacial “real estate,” so that the adhesive strength of the assembly is not compromised. On the other hand, owing to a lower stress level in an assembly with thin legs and large spacing, assurance of its interfacial strength is less of a challenge than for a conventional assembly with stiff, thick, and closely positioned legs. We show also that the thermal stresses not only in conventional TEM designs (using Be2Te3 as the thermoelectric material, and Sn-Sb solder), but also in the future high-power (and high operating temperatures) TEM design (using Si or SiGe as the thermoelectric material and Gold100 as the appropriate solder), might be low enough, so that the short- and long-term reliability of the TEM structure could still be assured. We have found, however, that thin-and-long legs should be considered for lower stresses, but not to an extent that appreciable bending deformations of the legs become possible. Future work will include, but might not be limited to, the finite-element computations and to experimental evaluations (e.g., shear-off testing) of the stress-at-failure for the TEMs of interest.

Optimum Design of Inductors Used for Wireless Power Transmission Micro-Module

2004 ◽  
Author(s):  
Chao-Liang Chang ◽  
Uei-Ming Jow ◽  
Chao-Ta Huang ◽  
Hsiang-Chi Liu ◽  
Jr-Yuan Jeng ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Electrical Properties ◽  
Optimum Design ◽  
Thermal Loading ◽  
Power Transmission ◽  
Thermal Strain ◽  
Electrical Performance ◽  
Wireless Power ◽  
Wireless Power Transmission ◽  
Analysis Software

The micro-inductor is a key component in wireless power transmission micro modules. In this paper, an optimum design for the micro-inductor was studied and related MEMS fabrication techniques were also developed. Commercial electromagnetic property analysis software, ANSOFT, was used to screen the main design factors of the micro-inductor. It was found that the high inductance and high quality factors of the micro-inductor implied high power transmission efficiency for the micro-module’s wireless power transmission. The electrical performance of the micro-inductor was affected by the thermal stress and thermal strain induced in the operational environment of the wireless power transmission micro-module. In order to investigate the reliability of the micro-inductor, commercial stress analysis software, ANSYS, was used to calculate thermal stress and thermal strain. The deformed model of the micro-inductor was then imported into ANSOFT in order to calculate its electrical properties. Glass substrate Pyrex 7740 was used to reduce the substrate loss of the magnetic flux of the micro-inductor. The surface micromachining technique, a kind of MEMS processing, was chosen to fabricate the micro-inductor; the coil of the micro-inductor was electroplated with copper to reduce the series resistance. The minimum line width and line space of the coil were 20 μm and 20 μm respectively. Polyimide (PI) was used for supporting the structure of micro-inductors. The maximum shear stress was 74.09MPa and the maximum warpage was 2.197 μm at a thermal loading of 125°C. For the simulated data, the most suitable areas for 31-turn and 48-turn coils were at an area ratio of 1.27 and 2, respectively. The electrical properties of the inductors changed slightly under thermal loading.

Thermoelectric module design to improve lifetime and output power density

2021 ◽  
Vol 18 ◽  
pp. 100391
Author(s):  
W. Sun ◽  
R. Sui ◽  
G. Yuan ◽  
H. Zheng ◽  
Z. Zeng ◽  
...  
Keyword(s):  
Power Density ◽  
Output Power ◽  
Thermoelectric Module ◽  
Module Design

Growth Kinetics and Thermal Stress in AlN Bulk Crystal Growth

2002 ◽  
Author(s):  
Bei Wu ◽  
Ronghui Ma ◽  
Hui Zhang ◽  
Michael Dudley ◽  
Raoul Schlesser ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Crystal Growth ◽  
Temperature Distribution ◽  
Stress Level ◽  
Grown Crystal ◽  
Power Level ◽  
Chemical Species ◽  
Group Iii Nitrides ◽  
Minor Effect ◽  
Group Iii

Group III nitrides, such as GaN, AlN and InGaN, have attracted a lot of attention due to the development of blue-green and ultraviolet light emitting diodes (LEDs) and lasers. In this paper, an integrated model has developed based on the conservation of momentum, mass, chemical species and energy together with necessary boundary conditions that account for heterogeneous chemical reactions both at the source and seed surfaces. The simulation results have been compared with temperature measurements for different power levels and flow rates in a reactor specially designed for nitride crystal growth at NCSU. It is evident that the heat power level affects the entire temperature distribution greatly while the flow rate has minor effect on the temperature distribution. The results also show that the overall thermal stress level is higher than the critical resolved shear stress, which means thermal elastic stress can be a major source of dislocation density in the as-grown crystal. The stress level is strongly dependent on the temperature gradient in the as-grown crystal. Results are correlated well with defects showing in an X-ray topograph for the AlN wafer.

Numerical Optimization of Silicon Stacked Module for 3-D Packaging Applications

2008 ◽  
Vol 5 (2) ◽  
pp. 68-76
Author(s):  
Akella G.K. Viswanath ◽  
Xiaowu Zhang ◽  
Y.Y. Wang ◽  
S.W. Yoon ◽  
Navas Khan ◽  
...  
Keyword(s):  
Solder Joint ◽  
Functional Integration ◽  
Three Dimensional ◽  
Interfacial Stress ◽  
Electrical Performance ◽  
Thickness Variation ◽  
Element Analysis ◽  
Variation Of Parameters ◽  
Optimization Study ◽  
Electroplated Copper

Three-dimensional package format has gained more popularity for various applications because of the trend toward higher functional integration, miniaturization, and better electrical performance. This paper presents a design optimization study of a 3-D package using a silicon interposer. The package consists of three stacks with five dies. Electrical connections through the silicon interposers are done by through-silicone vias (TSVs) filled with electroplated copper. Initially, structural optimization of the package is conducted by a 2-D finite element analysis and later, statistical analysis is performed to estimate the coupled effects of parameters considered for the design. Carrier thickness variation is found to be the most significant effect on the package warpage. Interfacial stress between the copper plug and the silicon via hole has been investigated and reported. A 3-D model is constructed for the solder joint reliability study with SnAgCu material properties. Solder joint life with variation of parameters (i.e., board level underfill, higher standoff solder interconnect, and low CTE board) is studied, and all results are reported accordingly.

Large Form Factor Hybrid LGA Interconnects; Recent Applications and Technical Learning

2014 ◽  
Vol 2014 (1) ◽  
pp. 000550-000560 ◽  
Author(s):  
John Torok ◽  
Brian Beaman ◽  
William Brodsky ◽  
Shawn Canfield ◽  
Jason Eagle ◽  
...  
Keyword(s):  
Form Factor ◽  
System Integration ◽  
Mechanical Analysis ◽  
Electrical Performance ◽  
Bottom Surface ◽  
Printed Wiring Board ◽  
Module Design ◽  
External Cooling ◽  
Reliability Characteristics ◽  
Server Design

Recent high-end server design trends have continued to challenge electronic packaging engineers to design and integrate larger form factor land grid array (LGA) attached modules within their assemblies. These trends have included the application of larger, denser, organic packaged modules whose electrical performance and postencapsulation physical characteristics have been enabled by both the continued development of hybrid LGA connectors as well as new module actuation hardware designs. In this paper, we'll discuss these recent trends, including the specific technical attributes and challenges that need to be addressed to ensure a repeatable and reliable assembly design is developed. Initially, overviews of the latest connector and module design trends, including styles and physical sizes and their implications to the module's bottom surface metallurgy (BSM) flatness requirements, etc. are provided. Pursuant to this, recent system integration trending is reviewed; including both the module quantity per system assembly as well as module to module physical placements and how each of these impact printed wiring board (PWB) design (i.e., layer count, LGA site flatness, etc.) as well as the PWB assembly's solder processing characteristics (i.e., LGA pre- and post-solder attach contact co-planarity, etc.). Completing the application portion, is a description of some recent LGA actuation hardware and module external cooling apparatus designs (e.g., air-cooled heats sinks and water-cooling cold-plates and thermal interface materials (TIMs), etc.). The remaining portion of the paper is dedicated to the description of the mechanical analysis efforts completed to provide a fundamental understanding of the design's “as-assembled” attributes and a review of the associated evaluation completed to verify the integrated assembly's reliability characteristics. From the analysis methodology perspective, both the means of including each of the integrated assembly's key attributes (e.g., module mechanical construction and as encapsulated flatness, LGA contact compliance and stiffness as well as soldered contact coplanarity, TIM stiffness, actuation hardware, heat sink and cold-plate mechanical construction, etc.) and the resulting estimation of the predicted module internal TIM and hybrid-LGA's Pb-free soldered interface strains, actuation hardware stresses and LGA contact load variation are provided. Completing the discussion is a review of the variety of testing executed to validate the design's intended reliability. Included in this is a description of the test vehicle's design, the environmental stress testing conducted (i.e., mechanical pre-conditioning, accelerated thermal cycling (ATC), mixed flowing gas (MFG) and heat aging (HA), etc.) and the resulting data.

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