Jul 31, 2014 | V. G. Karpov, Department of Physics and Astronomy, University of Toledo.
Metal whiskers often grow across leads of electric equipment and electronic package causing current leakage or short circuits and raising significant reliability issues. The nature of metal whiskers remains a mystery after several decades of research. Here, the existence of metal whiskers is attributed to the energy gain due to electrostatic polarization of metal filaments in the electric field. The field is induced by surface imperfections: contaminations, oxide states, grain boundaries, etc. A proposed theory provides closed form expressions and quantitative estimates for the whisker nucleation and growth rates, explains the range of whisker parameters and effects of external biasing, and predicts statistical distribution of their lengths....
Publisher: University of Toledo
Jul 24, 2014 | Randy Schueller, Ph.D.
Wire bonding a die to a package has traditionally been performed using either aluminum or gold wire. Gold wire provides the ability to use a ball and stitch process. This technique provides more control over loop height and bond placement. The drawback has been the increasing cost of the gold wire. Lower cost Al wire has been used for wedge-wedge bonds but these are not as versatile for complex package assembly. The use of copper wire for ball-stitch bonding has been proposed and recently implemented in high volume to solve the cost issues with gold. As one would expect, bonding with copper is not as forgiving as with gold mainly due to oxide growth and hardness differences.
This paper will examine the common failure mechanisms that one might experience when implementing this new technology....
Publisher: DfR Solutions
DfR Solutions has world-renowned expertise in applying the science of Reliability Physics to electrical and electronics technologies, and is a leading provider of quality, reliability, and durability (QRD) research and consulting for the electronics industry.
College Park, Maryland, United States
Jul 17, 2014 | Darren Campo, Jens Weyant, Bryan Muzyka
Embedded computing systems used in many military and avionics applications are trending toward higher heat fluxes, and as a result performance is being hindered by thermal limitations. This is intensified by the high ambient conditions experience by today’s modern warfighter. In many applications liquid cooling is replacing air flow through chassis for both thermal and environmental benefits(...)
This paper outlines a series of passive thermal improvements which are easily integrated into legacy, or existing, systems and can provide a 3-4x increase in dissipated power....
Publisher: Advanced Cooling Technologies
Jul 10, 2014 | Ren Huai-Hui, Wang Xi-Shu
This paper studies and compares the effects of pull–pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package.
The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure....
Publisher: Tsinghua University
Jul 02, 2014 | Jong-Myeong Park, Seung-Hyun Kim, Young-Bae Park - Andong National University, Myeong-Hyeok Jeong - NEPES Corporation.
Growth behaviors of intermetallic compounds (IMCs) and Kirkendall voids in Cu/Sn/Cu microbump were systematically investigated by an in-situ scanning electron microscope observation. Cu–Sn IMC total thickness increased linearly with the square root of the annealing time for 600 h at 150°C, which could be separated as first and second IMC growth steps. Our results showed that the growth behavior of the first void matched the growth behavior of second Cu6Sn5, and that the growth behavior of the second void matched that of the second Cu3Sn. It could be confirmed that double-layer Kirkendall voids growth kinetics were closely related to the Cu–Sn IMC growth mechanism in the Cu/Sn/Cu microbump, which could seriously deteriorate the mechanical and electrical reliabilities of the fine-pitch microbump systems...
Publisher: Nepes Corporation
Jun 26, 2014 | Steven Perng, Tae-Kyu Lee, and Cherif Guirguis - Cisco Systems, Inc., Edward S. Ibe - Zymet, Inc.
Edgebond adhesives have been widely used by the industry for improving the shock performance of area array packages. Most of the studies focus on the impact of material properties, such as coefficient of thermal expansion (CTE) and glass transition temperature (Tg), on reliability at room temperature. However, the operating temperature of a component on the printed circuit board bonded with edgebond adhesive can be close to or exceed Tg of the adhesive, where the material properties may be very different than at room temperature....
Publisher: Cisco Systems, Inc.
Jun 23, 2014 | John Maxwell, Director of Product Development, Johanson Dielectrics Inc.
It was unusual to see chip terminations change colors when tin lead solders were used but with the introduction of lead free reflow soldering and the corresponding increases in reflow temperatures terminations are now changing colors. Two conditions are present when reflow temperatures are increased for lead free solder alloys that leads to discoloration. Reflow temperatures are above the melting point of tin (Sn MP is 232oC). Air temperatures commonly used in forced convection reflow systems are high enough to both melt the tin plating on the termination allowing it to be pulled into the solder joint due to solder joint liquid solder surface tension leaving behind the exposed nickel barrier. Now those metal oxide colors will be visible due to high air temperatures during reflow....
Publisher: Johanson Dielectrics, Inc.
Jun 19, 2014 | Y.C. Liang, H.W. Lin, H.P. Chen, C. Chen, K.N. Tub, Y.S.Lai
For high-density electronic packaging,the application of flip-chip solder joints has been well received in the microelectronics industry. High-lead(Pb) solders such as Sn5Pb95 are presently granted immunity from the RoHS requirements for their use in high-end flip-chip devices, especially in military applications. In flip-chip technology for consumer electronic products, organic substrates have replaced ceramic substrates due to the demand for less weight and low cost. However, the liquidus temperatures of high-Pb solders are over 300°C which would damage organic substrates during reflow because of the low glass transition temperature. To overcome this difficulty, the composite solder approach was developed......
Publisher: National Chiao Tung University
Jun 12, 2014 | Arijit Roy
Occurrence of popcorn in IC packages while assembling them onto the PCB is a well known moisture sensitive reliability issues, especially for surface mount packages. Commonly reflow soldering simulation process is conducted to assess the impact of assembling IC package onto PCB. A strain gauge-based instrumentation is developed to investigate the popcorn effect in surface mount packages during reflow soldering process. The instrument is capable of providing real-time quantitative information of the occurrence popcorn phenomenon in IC packages. It is found that the popcorn occur temperatures between 218 to 241°C depending on moisture soak condition, but not at the peak temperature of the reflow process. The presence of popcorn and delamination are further confirmed by scanning acoustic tomography as a failure analysis....
A scholarly open access, peer-reviewed, interdisciplinary, monthly and fully refereed journal focusing on theories, methods and applications in Science, Engineering and Technology.
Riverside, Connecticut, United States
Jun 05, 2014 | Dr. Mike Bixenman, Debbie Carboni, Jason Chan
Stencil printing capability is becoming more important as the range of component sizes assembled on a single board increases. Coupled with increased component density, solder paste sticking to the aperture sidewalls and bottom of the stencil can cause insufficient solder paste deposits and solder bridging. Yield improvement requires increased focus on stencil technology, printer capability, solder paste functionality and understencil cleaning.
(...) The purpose of this research is to study the wipe sequence, wipe frequency and wipe solvent(s) and how these factors interact to provide solder paste printing yield improvement....
Publisher: Kyzen Corporation