0


IN MEMORIAM

J. Electron. Packag. 1996;118(4):i. doi:10.1115/1.2792165.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS

J. Electron. Packag. 1996;118(4):193-200. doi:10.1115/1.2792152.

Much research has been done on Surface Mount Technology (SMT) using the Finite Element Method (FEM). Little of this, however, has employed fracture mechanics and/or continuum damage mechanics. In this study, we propose two finite element approaches incorporating fracture mechanics and continuum damage mechanics to predict time-dependent and temperature-dependent fatigue life of solder joints. For fracture mechanics, the J-integral fatigue formula, da/dN = C(δJ)m , is used to quantify fatigue crack growth and the fatigue life of J-leaded solder joints. For continuum damage mechanics, the anisotropic creep-fatigue damage formula with partially reversible damage effects is used to find the initial crack, crack growth path, and fatigue life of solder joints. The concept of partially reversible damage is especially novel and, based on laboratory tests we have conducted, appears to be necessary for solder joints undergoing cyclic loading. Both of these methods are adequate to predict the fatigue life of solder joints. The advantage of the fracture mechanics approach is that little computer time is required. The disadvantage is that assumptions must be made on the initial crack position and the crack growth path. The advantage of continuum damage mechanics is that the initial crack and its growth path are automatically evaluated, with the temporary disadvantage of requiring a lot of computer time.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):201-205. doi:10.1115/1.2792153.

Lead coplanarity is defined as the height of a packaged device lead above the seating plane on which the device rests. The yield of a mass reflow surface mount soldering assembly process depends on lead coplanarity since, clearly, an excessive coplanarity is likely to produce an “open” between the lead and circuit pad. Furthermore, even if a marginal joint is obtained, excessive coplanarity can lead to reliability problems. Since these issues become more important as lead sizes decrease and pitches are refined, it is important to achieve a better understanding of coplanarity. This report analyzes the nature of 86,016 coplanarity measurements of 0.4 mm pitch, 256 I/O QFP devices. Four components to the coplanarity are identified and the distribution of each is modeled. When the four components are recombined, the result is a probability distribution for coplanarity. This information is required as input to an assembly yield model where parameter variations and tolerances are analyzed to predict surface mount yields.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):206-213. doi:10.1115/1.2792154.

Analysis of interfacial delamination for multichip module thin-film interconnects (MCM/TFI) is the primary objective of this paper. An interface crack model is integrated with finite-element analysis to allow for accurate numerical evaluation of the magnitude and phase angle of the complex stress intensity factor. Under the assumption of quasi-static delamination growth, the fate of an interfacial delamination after inception of propagation is determined. It is established that whether an interfacial delamination will continue to grow or become arrested depends on the functional behavior of the energy release rate and loading phase angle over the history of delamination growth. This functional behavior is numerically obtained for a typical MCM/TFI structure with delamination along die and via base, subjected to thermal loading condition. The effect of delamination interactions on the structural reliability is also investigated. It is observed that the delamination along via wall and polymer thin film can provide a benevolent mechanism to relieve thermal constraints, leading to via stress relaxation.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):214-222. doi:10.1115/1.2792155.

The thermomechanical response of ball-grid array assemblies during reflow soldering is considered here. Experiments are performed to investigate the thermomechanical response of a representative system and the results are used to validate a numerical model of system behavior. The conclusions drawn from the experimental studies are used to guide development of a process model capable of describing more realistic BGA soldering scenarios. Process model predictions illustrate the system’s thermomechanical response to thermal and mechanical processing conditions, as well as component properties. High thermal conductivity assemblies show the greatest sensitivity to mechanical loading conditions.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):223-228. doi:10.1115/1.2792156.

As part of a major project to develop a computer-based model to support the product and process design activity for reflow soldered assemblies, it has been found necessary to carry out fundamental investigations of the processes occurring as solder pastes approach and pass the reflow temperature. This paper presents the results and our interpretation of the observed physical phenomena arising from recent high-speed video microscopy studies of the reflow of bulk deposits of solder paste and also of the formation of solder joints during infrared reflow soldering. These studies have provided insights into the physical phenomenology of reflowing solder paste, the interpretation of wetting curves and the mechanisms behind the formation of manufacturing driven defects.

Topics: Solder joints
Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):229-234. doi:10.1115/1.2792157.

Thin film metallizations are one of the most important interconnects in large-scale integrated circuits. They are covered by substrates and passivation films. Large hydrostatic (mean) tension develops due to the constraint and thermal mismatch, and voiding is identified as the failure mechanism. This phenomenon of rapid nucleation and growth of voids is called cavitation instability and it can lead to the failure of ductile components in electronic packages such as metallizations. A micromechanics model is developed to provide the critical mean stress level that will trigger the cavitation instability. It is found that this critical mean stress level the cavitation stress, not only depends on the material properties but also is very sensitive to defects in the material. For example, the cavitation stress decreases drastically as the void volume fraction increases. The stress-based design criterion for ductile components in electronic packages should then be: (1) Von Mises effective stress < yield stress; and (2) mean stress < cavitation stress, which is particularly important to the constrained ductile components in electronic packages such as vias and conductive adhesives. An analytical expression of cavitation stress for elastic-perfectly plastic solids is obtained, and numerical results for elastic-power law hardening solids are presented.

Topics: Stress
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):244-249. doi:10.1115/1.2792159.

The rapid advancement of integrated circuits and associated electronic technologies have placed increasing demands on electronic packaging and its material structures in terms of the reliability requirements. In addition to the thermally induced stresses, electronic packages often experience dynamic external loads during shipping, handling, and/or operation. This is especially important for automotive, military, and commercial avionics operating environments. These dynamic loads give rise to large dynamic stresses in the leads causing fatigue failures. For peripheral leaded packages the corner leads are the most highly stressed leads. This paper addresses the determination of the out-of-plane displacement of the corner leads of peripheral leaded components when the local peripheral leaded component/board assembly is subjected to bending moments in two directions. The solution is achieved by using a combination of Finite Element Analysis (FEA), Design of Experiments (DOE), and analytical techniques. The out-of-plane displacement can then be applied as a boundary condition on a local lead model to determine the stresses which in turn can be used to estimate the fatigue life.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):250-257. doi:10.1115/1.2792160.

The flow and heat transfer characteristics in a forced-air cooled electronic device are calculated with a two-fluid model of turbulence. The fluids are defined as turbulent and nonturbulent, and precludes the need for low-Reynolds number model in the near-wall regions. Transport equations are solved for the zone-averaged variables of each fluid. Empirical relations, established in prior work, are used to express interchange of mass, momentum, and energy at the interface. Gradient-diffusion flux is considered an intrafluid source of turbulence. Several cases are considered showing effects of Reynolds number and heat-dissipation density on the flow and thermal fields. A critical comparison is made between the results based on the application of this model and the conventional k -ε model. Such results include velocity vectors and temperature distribution. In addition, the two-fluid model predicts spatial distribution of the intermittency factor, which provides a measure of the extent of turbulence and mixing in the electronic system.

Topics: Cooling , Fluids , Turbulence
Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):258-263. doi:10.1115/1.2792161.

This paper presents an investigation into the various factors which influence the peak average inside air temperature of outdoor telephone switching cabinets. The primary goal is to determine which factors are important and to develop a correlation which will predict peak average air temperatures inside the cabinet under a variety of situations. A network of lumped thermal capacitances and resistances is used to model the transient thermal behavior of the electronics enclosure. Energy balances for each element are developed creating a system of ordinary differential equations which are solved using a fourth order Runge-Kutta method. The numerical model is verified by comparison to experimental data. A search of parameters which affect the thermal behavior of telephone switching cabinets is conducted. A sensitivity analysis is performed to determine the important terms. Parametric studies are conducted to develop a correlation which relates the internal cabinet air temperature to the important dimensionless parameters.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):264-270. doi:10.1115/1.2792162.

Boiling jet impingement heat transfer from a simulated electronic chip to Fluorinert FC-72 within a clamshell avionic module was investigated for dependence upon inlet fluid temperature, nozzle diameter, nozzle to chip spacing, jet velocity, and chip length. The clamshell module was designed and fabricated to accommodate both single and multiple chip boards and to demonstrate the feasibility of an ultra-high power (on the order of several kilowatts) module. Critical heat flux (CHF) was found to be directly dependent upon subcooling and jet velocity, but relatively unaffected by the nozzle to chip spacing variations examined. The effect of varying the chip size was evaluated and found to produce higher CHF values as chip size was decreased. A correlation accounting for both geometric and subcooling effects was adapted to predict the CHF database with a mean absolute error of 9.6 percent. The module is shown to be capable of dissipating a heat load of 12,000 W at a module flow rate of 8.01 × 10−4 m3 /s (12.7 gpm), thus eclipsing the current technology available in avionic cooling.

Commentary by Dr. Valentin Fuster
J. Electron. Packag. 1996;118(4):271-279. doi:10.1115/1.2792163.

An analytically based approximate solution is presented for the thermal resistance of an axisymmetric heat source mounted on a conductive substrate with bottom- and top-side convective cooling of the substrate. The approximation closely matches an exact solution for bottom-side convective cooling and reference finite element solutions for top-side and both-side cooling over broad ranges of substrate thickness (10−4 ≤ t* ≤ 104 and 10−2 ≤ t* ≤ 102 ), substrate outer radius (1 ≤ b* ≤ 100) and convective Blot numbers (10-4 to 102 ). With bottom-side cooling, a minimum in the thermal resistance can occur over a wide range of substrate thicknesses. The approximate solution possesses simplicity and ease of computation as compared to exact or computational solutions for many microelectronic applications.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEF

J. Electron. Packag. 1996;118(4):280-284. doi:10.1115/1.2792164.

The effects of cycling frequency and temperature on the fatigue life of solder has been analyzed. Mechanical fatigue life experiments were conducted under load control while varying the temperature and cycling frequency. Using the experimental data, a fatigue model was formulated based on the Basquin and the Coffin-Manson relations, introducing the effects of temperature and frequency. The model parameters were obtained by a statistical method incorporating multiple linear regression. Using the model, estimated values of cycles to failure at each of the testing temperatures and frequency were calculated. Using the estimated values, an evaluation of each of the models was conducted, resulting in strong correlations between the model’s estimation and the experimental data.

Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In