Papers by Keyword: Electronic Packaging

Abstract: Since the environmental regulations of Reduction of Hazardous Substances (RoHS) directive came into effect in Europe and Asia on July 1, 2006, requiring the removal of any lead (Pb) content from the electronics industry, the issue of tin (Sn) whisker growth from pure Sn and SnPb-free alloys has become one of the most imperative issues that need to be resolved. Moreover, with the increasing demand for electronics miniaturization, Sn whisker growth is a severe threat to the reliability of microelectronic devices. Sn whiskers grow spontaneously from an electrodeposited tin coating on a copper substrate at room temperature, which can lead to well-documented system failures in electronics industries. The Sn whisker phenomenon unavoidably gives rise to troubles. This paper briefly reviews to better understand the fundamental properties of Sn whisker growth and at the same time discover the effective mitigation practices for whisker growth in green electronic devices. It is generally accepted that compressive stress generated from the growth of Cu₆Sn₅ intermetallic compound (IMC) is the primary driving force for Sn whisker growth during room temperature storage. It is, therefore, important to determine that the relationship between IMC growth and Sn whisker growth. Reduction of stress in the IMC layer can therefore reduce the driving force for whisker formation and be used as a means for whisker mitigation. To date, there are no successful methods that can suppress the growth of Sn whisker as efficient as Pb addition. It is hoped that the Sn whisker growth mechanisms are understood better in the future, with better measuring and monitoring methodologies and systems being developed, the real solutions may be eventually developed to eliminate or mitigate the Sn whisker problems of green reliability lead-free electronic assemblies.

Abstract: The fabrication and thermal physical properties contain thermal conductivity (TC) and coefficient of thermal expansion (CTE) using 40%、50%、60% vol% β-SiC particle reinforced Al composite for electronic packaging respectively have been analyzed. The composites were produced by ball milling and pressing method. The composite which fabricated by tri-sized β-SiC particle with a weight ratio of 17:7:1,vol% of 50% and 60%.The dense and morphology were investigated. The relationship between volume fraction of β-SiC particle and thermal physical properties was discussed. Changed the volume fraction of β-SiC particle will led to a decreasing or increasing of TC and CTE. It found that values of TC and CTE were achieved their maximum balance when using tri-sized β-SiC particle of 160μm ,125μm as well as 38μm with a weight ratio of 17:7:1 and 50%vol of β-SiC particle reinforcing.

Abstract: Copper based composites with 30, 40, 50 and 60 vol.% Al₂O₃ were fabricated by powder metallurgy and consolidated by pulsed electric current sintering (PECS). For the purpose of determining the advantage of using coated fillers, composite alumina particles with 18 vol.% copper were prepared by electroless copper plating. Coatings were continuous and homogeneous through alumina surface. Thus, composites consolidated by the modified process increased contact between the matrix and filler, which resulted in superior thermo-physical properties. Thermal conductivities of 210-99 and 227-114 W/mK were obtained for Cu/Al₂O₃ made by the admixture and the coated filler method, respectively. Such superiority is mainly attributed to the continuity in the matrix phase; the thermal conductivity values observed are similar to those shown by the traditional materials used in electronic packaging. The coefficient of thermal expansion was slight lower in composites fabricated by the coated filler method; values in the ranges of 14-11 and 13-10.5 μm/m°C were obtained for the admixture and the coated filler method, respectively.

Abstract: Scanning Acoustic Microscopy (SAM) has been a powerful non-destructive testing tool used in electronic packaging and material characterization. With the development of 3D electronic packaging, internal dimensions of electronic packaging are getting more and more smaller, and the detection accuracy of existing non-destructive testing technology is far behind the requirements of manufacturing technology. In this study, a set of practical SAM system was developed independently by our Lab. And its detection resolution was analyzed using high frequency focused transducers with center frequency ranging from 20 MHz to 100MHz. The experimental results show that the lateral resolution of the ultrasonic transducer with 100MHz central frequency can reach about 40 microns, which is consistent with calculated resolution. Comparing with Sparrow criteria, Rayleigh criteria is more coherent with the experimental results.

Abstract: In this paper, the effects of strengthening epoxy matrices with nanopowders are discussed. Investigate the changes of reaction viscosities after adding different hardeners, nanoparticles and diluents to the polymer matrices. Analyze the applications to the automatic electronic packaging. The results show that different species in the curing reaction systems of epoxy will affect flow stabilities. Reaction viscositiesare affected primarily by the choice of hardeners. Nanoparticles will increase system viscosities and shorten matrix resin gel time. Adding diluents will help spread the powders and material flows in the systems, but is relatively not good for stability.

Abstract: Due to the initiate failure from the interface of solder and singularity of stress and strain field in the area, new fatigue life laws based on equivalent intensity ranges are proposed. The thermal fatigue tests are carried out. With observation by scanning electron microscope (SEM), the cracks begin from the interface of the chip, and propagate along the interface and/or grow with zigzag shape in the solder. Relative tube voltage drop (TVD) as a parameter is conducted to determine the fatigue damage accumulation and the number of thermal cycles for initiate crack growth. The singular field from the interface edge of the chip is obtained from numerical analyses by sub-modeling technique. Two types of solder materials of Sn-3Ag-0.5Cu and Pb-5Sn with new viscous creep constitutive relationship are used. The constitutive model compose of linear curve for small stress and hyperbolic sine form for high stress, respectively. Two shocks are found in one cycle from numerical simulation. Compared the fatigue life from the experiment observation with the numerical prediction, it is noticed that the new fatigue laws do not depend on an artificial point near the interface edge in a chip, and give reasonable and reliable results.

Abstract: in order to resolve the weaker wettability between the copper and SiC particles and analyze the micro-structure and thermal conductivity properties of the SiCp/Cu composites, the chemical plating technology and pressure-less sintering technique were utilized to fabricate SiCp/Cu composites. The results proved that SiC powders were more homogeneous in the SiCp/Cu composites and interfaces were clear. The coefficients of linear expansion of SiCp/Cu composites were nonlinear increased along with the measuring temperature increasing. When SiC content was constant, the coefficients of thermal expansion (CTE) and thermal conductivity (TCT) of the SiCp/Cu composites would reduce as the content of the SiC powder became higher.

Abstract: While aluminum-based metallization schemes on Si have been optimized for the last decades, only few investigations have been done on copper metallization with SiC-devices. Thus, in this work the mechanical as well as the electrical interactions of this metallization system have been analyzed and optimized for SiC-devices in high reliability applications. For optimizing the adhesion of the copper metallization stack on SiC devices, different metallization schemes consisting of adhesion promoters (Ti, Cr, Al, Ta, WTi), diffusion barriers (TiN, Ta, WTi), and the final copper layer have been tested by peel-tests. For investigating the electrical interactions TLM measurements as well as leakage-current measurements have been done on copper metalized SiC samples.

Abstract: Multi-walled carbon nanotube (MWCNT) reinforced copper nanocomposites were prepared using a unique spherical MWCNT-implanted copper composite powders. The MWCNTs are homogenously ‘locked’ in the composite and tightly bonded to the matrix, which makes them play excellent reinforcement role on the microhardness compared with the unreinforced pure copper. Although the thermal conductivity is not enhanced for the thermal resistance between the carbon nanotubes and the copper matrix; it is still high enough to be used as electronic packaging materials even the concentration of MWCNTS in the composite is up to 5 wt%. Furthermore, the thermal expansion of the composites decreased apparently with the addition of the carbon nanotubes.

Abstract: The β-SiCp/Al electronic packaging composites with excellent performance were successfully fabricated by pressureless infiltration technology in air.The effects of alloying elements, infiltration temperature and time on infiltration process and application of -SiC were studied.The results show that by adding appropriate magnesium to aluminum matrix, a interface reaction between oxide films of SiC and magnesium occurs, and the interface reaction product MgAl2O4 is generated, the interface wettability of Al and SiC and pressureless infiltration are improved.The interface harmful phase Al4C3 can be inhibited by adding silicon to aluminum matrix.Identified 850°C for the best infiltration temperature, and the thickness with infiltration time and larger, infiltration rate is about 10mm/hour.Under the same parameter conditions, the thermal properties of β-SiCp/Al electronic packaging material are 4 ~ 6% higher than that of ɑ-SiCp/Al. The β-SiCp/Al electronic packaging materials with 66% SiC volume ratio has lower coefficiency of thermal expansion than those ɑ-SiCp/Al electronic packaging materials.And the thermal expansion coefficient and thermal conductivity of β-SiCp/Al electronic material can satisfy the requirements for electronic packaging materials.