On Failure Mechanisms in Flip Chip Assembly—Part 1: Short-Time Scale Wave Motion

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Yoonchan Oh ◽  
C. Steve Suh ◽  
Hung-Jue Sue
Keyword(s):  
Time Scale ◽  
Wave Motion ◽  
Flip Chip ◽  
Thermal Stresses ◽  
Failure Modes ◽  
Coefficient Of Thermal Expansion ◽  
Short Time Scale ◽  
Time Frequency ◽  
Thermal Transients ◽  
Short Time

The demand for higher clock speed and larger current magnitude in high-performance flip chip packaging configurations of small footprint has raised the concern over rapid thermal transients and large thermal spatial gradients that could severely compromise package performance. This paper explores coupled electrical-thermal-mechanical multiphysics to evaluate the concern and to establish the knowledge base necessary for improving flip chip reliability. It is found that within the first few hundreds of nanoseconds after power-on, there are fast-attenuating, dispersive stress waves of extremely high frequency propagating in the package. The concepts of high cycle fatigue, power density, and joint time-frequency analysis are employed to characterize the waves along with the various damage modes resulting from the propagation of these short-lived dynamical disturbances in bulk materials and along bimaterial interfaces. A qualitative measure for failure is developed to evaluate the extent of damage inflicted by short-time wave motion. Damages identified in this study are in agreement with physical failure modes commonly seen in industry, thus implying that micron scale cracks or interfacial adhesion flaws initiated at the short-time scale would be further propagated by the coefficient of thermal expansion induced thermal stresses at the long-time scale and result in eventual electrical disruptions.

On Failure Mechanisms in Flip Chip Assembly—Part 2: Optimal Underfill and Interconnecting Materials

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Yoonchan Oh ◽  
C. Steve Suh ◽  
Hung-Jue Sue
Keyword(s):  
Time Scale ◽  
Flip Chip ◽  
Thermal Stresses ◽  
Failure Modes ◽  
Scale Effects ◽  
Short Time Scale ◽  
Long Time ◽  
Solder Joint Fatigue ◽  
Scale Properties ◽  
Short Time

The physics explored in this investigation enables short-time scale dynamic phenomenon to be correlated with package failure modes such as solder ball cracking and interlayer debond. It is found that although epoxy-based underfills with nanofillers are shown to be effective in alleviating thermal stresses and improving solder joint fatigue performance in thermal cycling tests of long-time scale, underfill material viscoelasticity is ineffective in attenuating short-time scale propagating shock waves. In addition, the inclusion of Cu interconnecting layers in flip chip area arrays is found to perform significantly better than Al layers in suppressing short-time scale effects. Results reported herein suggest that, if improved flip chip reliability is to be achieved, the compositions of all packaging constituent materials need be formulated to have well-defined short-time scale and long-time scale properties. Chip level circuit design layout also needs be optimized to either discourage or negate short-time wave propagation. The knowledge base established is generally applicable to high performance package configurations of small footprint and high clock speed. The approach along with the numerical procedures developed for the investigation can be a practical tool for realizing better device reliability and thus high manufacturing yield.

Time-Frequency Representation of Inspiratory Motor Output in Anesthetized C57BL/6 Mice In Vivo

2005 ◽  
Vol 93 (3) ◽  
pp. 1762-1775 ◽  
Author(s):  
Marvin H. O'Neal ◽  
Evan T. Spiegel ◽  
Ki H. Chon ◽  
Irene C. Solomon
Keyword(s):  
Spectral Analysis ◽  
Time Scale ◽  
Spectral Power ◽  
Short Time Scale ◽  
Time Varying ◽  
Spectral Activity ◽  
Time Frequency ◽  
Inspiratory Motor ◽  
Short Time ◽  
Time Invariant

Inspiratory motor discharges, in addition to long-time-scale rhythmic oscillatory bursting, exhibit short-time-scale rhythmic oscillations that have been identified, and subsequently characterized, using power spectral analyses [predominantly fast-Fourier transforms (FFT)]. These analyses assume that the signal being analyzed is stationary; however, this is not the case for most biological signals, which exhibit varying degrees of nonstationarity. To overcome this limitation, time-frequency methods, which provide not only the frequency content but also information regarding the timing of these fast rhythmic oscillations (i.e., dynamics of spectral activity), should be used. Thus this study was performed to investigate the dynamic or time-varying features of spectral activity in inspiratory motor output. Both conventional time-invariant and time-frequency (time-varying) spectral analysis methods were performed on recordings of diaphragm EMG, phrenic nerve, and hypoglossal nerve discharges obtained from spontaneously breathing urethan-anesthetized adult C57BL/6 mice. Conventional time-invariant spectral analysis using a FFT algorithm revealed three dominant peaks in the power spectrum, which were located at 1) 20–46, 2) 83–149, and 3) 177–227 Hz. Time-frequency spectral analysis using a generalized time-frequency representation (TFR) with the smoothed pseudo-Wigner-Ville distribution (SPWD) kernel confirmed the general location of these spectral peaks, identified additional spectral peaks within the frequency ranges described above, and revealed a time-dependent expression of spectral activity within the inspiratory burst for each of the frequency ranges. Furthermore, this method revealed that 1) little or no spectral activity occurs during the initial portion of the inspiratory burst in any of the frequency ranges identified, 2) transient oscillations in the magnitude of spectral power exist where spectral activity occurs, and 3) total spectral power exhibits an augmenting pattern over the course of the inspiratory burst. These data, which provide the first description of spectral content in inspiratory motor discharges in adult mice, show that both time-invariant and time-varying spectral analysis methods are capable of identifying short-time-scale rhythmic oscillations in inspiratory motor discharge (as expected); however, the dynamic (i.e., timing) features of this oscillatory activity can only be obtained using the time-frequency method. We suggest that time-frequency methods, such as the SPWD, should be used in future studies examining short-time-scale (fast) rhythmic oscillations in inspiratory motor discharges, because additional insight into the neural control mechanisms that participate in inspiratory-phase neuronal and motoneuronal synchronization may be obtained.

On the Dynamic Short-Time Scale Wave Propagation and the Characterization of Optimal Packaging Material for High Performance Electronic Packages

2002 ◽  
Author(s):  
Yoonchan Oh ◽  
C. Steve Suh ◽  
H.-J. Sue
Keyword(s):  
Time Scale ◽  
High Performance ◽  
Spectral Characteristics ◽  
Short Time Scale ◽  
Electronic Packages ◽  
Transient Wave ◽  
Dispersive Waves ◽  
Thermal Transients ◽  
Short Time ◽  
Package Reliability

The demand for higher clock speed and higher level of integration, and, at the same time, smaller die size for high-performance electronic packages has accompanied by a drastic increase in package power consumption and dissipation. Large transient thermal gradients are thus experienced upon each power-on. Unlike thermal cycling test which is usually performed to evaluate the fatigue life of solder joints, rapid thermal transient is of major concern for overall package reliability. This rapid transient at short-time scale suggests that dynamic thermal-mechanical phenomenon in packages needs to be fully understood and the associated failure mechanisms identified for improved microelectronic reliability. In this study, how rapid thermal transients affect the generation, spectral characteristics, and interference of the induced stress waves propagating in high-density packaging configurations undergoing power cycling are investigated. The short-time effects facilitated by dispersive waves in current packaging configurations are studied and the possible mechanisms behind mechanical failures including solder cracking and delamination are discussed. Knowledge base thus established enables a set of guidelines to be proposed for developing new types of polymeric underfill material. Materials hence formulated would have optimal characteristics in response to the short-time effect to effectively discourage transient wave phenomena and thus improve the overall package reliability. The presented investigation provides a better understanding of the underlying physics governing the response of a high-performance package subject to rapid thermal-mechanical transients, which could potentially be the foundation for the formulation of new molecularly designed packaging materials and the associated manufacturing processes.

An Alternative Test Using Algal Cultures for Testing Chemicals for Toxicity

1993 ◽  
Vol 21 (2) ◽  
pp. 196-201
Author(s):  
Søren Achim Nielsen ◽  
Thomas Hougaard
Keyword(s):  
Size Distribution ◽  
Mitotic Activity ◽  
Time Scale ◽  
Test System ◽  
Short Time Scale ◽  
Toxic Substances ◽  
Alternative Test ◽  
Short Time ◽  
Algal Cultures ◽  
Test Cultures

An alternative test is presented, in which algal cultures are used for testing toxic substances. This test system is based on variations in the size distribution of cells in test cultures as a measurement of growth. Thus, inhibition of mitotic activity is used as a measurement for toxic effects. The test can be performed on a short time-scale and is very sensitive to even weak toxic doses.

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