Showing papers by "Fred Barlow published in 2014"

Thermal Cycling Reliability Study of Ag–In Joints Between Si Chips and Cu Substrates Made by Fluxless Processes

Abstract: The purpose of this research is to assess the reliability of Ag-In joints in thermal cycling (TC) environment. Si chips and Cu substrates were bonded using silver (Ag) and indium (In) multilayer structure without applying any flux. After bonding, the samples were annealed in air at 250 °C for 190 h to convert the joint into an alloy of small intermetallic grains and solid solution (Ag). The resulting joint has a melting temperature higher than 800 °C. Si-Cu pair was chosen because of the large coefficient of thermal expansion mismatch, i.e., 2.7 × 10-6/°C of Si versus 17 × 10-6/°C of Cu. Two TC tests were performed. All 10 samples passed 100 cycles of initial TC test between -40 °C and 85 °C. They were then subjected to 5000 cycles of TC test between -40 °C and 200 °C. Seven of ten samples survived beyond 5000 cycles. Three samples broke at 850, 2600, and 3000 cycles, respectively. The early failure was probably caused by imperfections and defects in the joints. Based upon these results, it seems that our Ag-In joints compare favorably with sintered silver joints. The Ag-In joints not only have high-melting temperature but also survive harsh TC environment.

Spectrally Accurate Causality Enforcement using SVD-based Fourier Continuations for High Speed Digital Interconnects

Abstract: We introduce an accurate and robust technique for accessing causality of network transfer functions given in the form of bandlimited discrete frequency responses. These transfer functions are commonly used to represent the electrical response of high speed digital interconnects used on chip and in electronic package assemblies. In some cases small errors in the model development lead to non-causal behavior that does not accurately represent the electrical response and may lead to a lack of convergence in simulations that utilize these models. The approach is based on Hilbert transform relations or Kramers-Kronig dispersion relations and a construction of causal Fourier continuations using a regularized singular value decomposition (SVD) method. Given a transfer function, non-periodic in general, this procedure constructs highly accurate Fourier series approximations on the given frequency interval by allowing the function to be periodic in an extended domain. The causality dispersion relations are enforced spectrally and exactly. This eliminates the necessity of approximating the transfer function behavior at infinity and explicit computation of the Hilbert transform. We perform the error analysis of the method and take into account a possible presence of a noise or approximation errors in data. The developed error estimates can be used in verifying causality of the given data. The performance of the method is tested on several analytic and simulated examples that demonstrate an excellent accuracy and reliability of the proposed technique in agreement with the obtained error estimates. The method is capable of detecting very small localized causality violations with amplitudes close to the machine precision.

Causality Verification Using Polynomial Periodic Continuations for Electrical Interconnects

Abstract: We present a method for checking causality of band-limited tabulated frequency responses. The approach is based on Kramers-Kronig relations and construction of periodic polynomial continuations. Kramers-Kronig relations, also known as dispersion relations, represent the fact that real and imaginary parts of a causal function form a Hilbert transform pair. The Hilbert transform is defined on an infinite domain, while, in practice, discrete values of transfer functions that represent high-speed interconnects are available only on a finite frequency interval. Truncating the computational domain or approximating the behavior of the transfer function at infinity causes significant errors at the boundary of the given frequency band. The proposed approach constructs a periodic polynomial continuation of the transfer function that is defined by raw frequency responses on the original frequency interval and by a polynomial in the extended domain, and requires the continuation to be periodic on a wider domain of a ...

Causality Enforcement of High-Speed Interconnects via Periodic Continuations

Abstract: Causality verification and enforcement is of great importance for performance evaluation of electrical interconnects. We present two techniques based on Kramers-Kronig dispersion relations, also called Hilbert transform relations, and construction of causal periodic continuations. The first method employes periodic polynomial continuations, while the second approach constructs Fourier continuations using a regularized singular value decomposition (SVD) method. Given a transfer function sampled on a bandlimited frequency interval, non-periodic in general, both approaches construct an accurate approximation on the given frequency interval by allowing the function to be periodic on an extended domain. This allows one to significantly reduce (for polynomial continuations) or even completely remove (for Fourier continuations) boundary artifacts that are due to the bandlimited nature of frequency responses. Using periodic continuations eliminates the necessity of approximating the transfer function behavior at ...

Electronic Packaging: Semiconductor Packages

Abstract: Electronic packages contain numerous transistors and integrated circuits, resistors, capacitors, inductors, diodes, in addition to other components, linked through interconnections to form various functional entities. As functional densities increase, the level of integration of the inner circuitry continues to increase on the chip level. Electronic packaging serves a few critical functions such as signal distribution, power distribution, thermal management, rigidity, mechanical stability, and circuitry protection.

Zero Meta-material Ferroelectric Phase Shifter Embedded inside LTCC

Abstract: This paper describes the design and processing of a zero meta-material phase shifter (ZMPS) embedded within a low temperature co-fired ceramics (LTCC) structure. The designed ZMPS is based on a composite right/left handed meta-material (CRLH MTM) transmission line approach. L-C networks were used to achieve zero phase shift at a specified frequency. The proposed design combines the advantages of an accurate zero phase shift using meta-material concepts and the advantages of passive components (capacitors and inductors) embedded inside LTCC to reduce device size, weight, and cost. The designed phase shifter provides an accurate 0o phase shift at 0.73 GHz with −16.7 dB return-loss and −0.31 dB insertion-loss at the center frequency. The paper also provides a comparison between BST and BZT as dielectric materials embedded inside LTCC with respect to the preparation process and shrinking effects.

Finite Element Analysis and Fatigue Life Prediction of an Aluminum Alloy Braze for High Temperature Thermoelectric Generator Package Assembly

Abstract: Thermoelectric generators (TEGs) are solid state devices that convert thermal energy into electrical energy using the Seebeck effect. They can be used for energy harvesting in trucks and passenger vehicles by taking advantage of the temperature difference between the exhaust pipes and ambient environment. The key issue with thermoelectric devices today is the demand for increased operating temperatures while maintaining adequate reliability and low cost. Since, TEGs are subjected to sub-critical thermal cyclic loading, ensuring satisfactory reliability is important for commercially viable products. TEGs used in passenger vehicles should be able to withstand extreme environmental conditions such as high temperature, shock and mechanical vibration [1]. Since the operating temperatures of TEGs can reach temperatures higher than 500 °C, aluminum brazes offer a good high temperature solution for die attach applications. The thermoelectric materials of TEGs are prone to oxidation and sublimation. A solution to minimize these phenomena is to enclose the TEG device in a hermetic package. This paper analyzes the reliability of aluminum alloy braze Al 718 (12% Si, 88% Al) used in TEG packages under fatigue loading. A power cycling temperature fluctuation method was employed to simulate the operating conditions of the TEGs for passenger vehicle. Low cycle fatigue simulations were performed using the direct cyclic approach embedded in the finite element software ABAQUS. Direct cyclic approach uses an extrapolation technique, which allows for efficient and computationally inexpensive simulations. The numerical model was validated using experimental test data. A validated damage model was used to analyze the cyclic damage evolution in the aluminum alloy braze for the hermetic TEG packages.Copyright © 2014 by ASME