Papers by Keyword: Electromigration

Abstract: Electromigration effects on the solder joint formation of 99.3Sn-0.7Cu and 96.5Sn-3.0Ag-0.5Cu lead-free solder with Cu electroplated Ni layer wire were investigated. The electromigration effects on the solder joints were studied after current density stressing at 1 x 10³ A/cm² in room temperature for 0 h, 120 h, and 240 h. The research work found that intermetallic compound (IMC) formation on the joint is increases for both solders with longer period of current stress applied. Higher IMC thickness growth in 99.3Sn-0.7Cu solder joint compared to 99.3Sn-0.7Cu is detected and both anode regions of the solder joints show higher IMC thickness growth compared to cathode region. Experimental results show 99.3Sn-0.7Cu solder joint is more prone to failure under current stress compared to 96.5Sn-3.0Ag-0.5Cu solder joint with thicker IMC which translates to higher brittleness.

Abstract: Three dimensional thermo-electrical finite element analysis was employed to simulate the current density and temperature distributions for solder bump joints with different bump shapes. Mean-time-to-failure (MTTF) of electromigration was discussed. It was found that as the bump volume increased from hourglass bump to barrel bump, the maximum current density increased but the maximum temperature decreased. Hourglass bump with waist radius of 240 μm has the longest MTTF.

Abstract: A series of electrokinetic experiments were conducted on fluorine-contaminated soil with different anolyte (NaOH) concentrations in a self-made electrolyzer to investigate the effects of anolyte concentration on removal of fluorine. Experimental results showed that anolyte concentration (0.1mol L^-1) was more suitable of the six anolyte concentration tested, in contrast to the removal efficiency of fluorine and the cost of the high concentration of anolyte. On this anolyte concentration that 57.75% fluorine could be removed from contaminated soil within 10 days under the applied voltage (1.0 V cm^-1). The results also indicated that electromigration was a dominant transport mechanism responsible for the removal of fluorine from contaminated soil than electroosmosis.

Abstract: The theoretical and experimental work is executed for study the impact of anneal on the grain size, electromigration (EM) reliability of copper (Cu) interconnect system, and subsequently find the optimized anneal condition. EM accelerated failure tests are carried on the Cu interconnect samples with 0.2μm line width, which are produced at different anneal conditions. It is shown that anneal can lead the grains to grow to become larger, and lessen the EM diffuse path. As a result, the EM diffuse active energy (Ea) of Cu interconnect is enhanced, and the ability against the EM of Cu interconnect is improved. By comparing the EM character of Cu interconnects produced at different anneal conditions, results can be obtained as below: the anneal time should be maintained 40 minutes at least in order to achieve fully anneal and excellent ability against the EM; the anneal temperature should be set about 350°C approximately, because high temperature (beyond 400°C) anneal can induce the other reliability issues, which will have a strong negative impact on the EM reliability. The results in this paper are significance for Cu interconnect technology optimize and are beneficial to improve the EM reliability of the Cu interconnect system.

Abstract: A frequent cause of failure of portable and hand-held devices is an accidental drop to the ground. The effect of electromigration on the mechanical properties of solder joints was discussed in this paper. Without current stressing, the samples were broken in the bulk of solder or at the interface of Al interconnect and solder. If the Al-solder interfacial mechanical strength was improved by changed the interfacial structure or optimized the jointing process, the flip chip devices would show the lonely ductile fracture in the bulk of solder. After electromigration the samples were broken abruptly at the interface near the chip side while the bulk of the solder joints maintained the original shape. Due to the interfacial reaction and the polarity effect of electromigration on the interfaces, a ductile solder joint can become a brittle solder joint. The ductile-to-brittle transition is very sensitive to a high speed shear stress applied to the joints. Because solder alloys are ductile by nature, it is of interest to understand how electromigration can influence the mechanical properties of solder joints’ interfaces and change their ductile nature. Owing to the polarity effect of electromigration, vacancies will accumulate to form voids at the cathode interface of solder joints. Besides, much more intermetallic compound formation at the joint interfaces also caused the ductile-to-brittle transition. Thus the interfaces become more and more brittle with time due to IMC formation or vacancy accumulation from electromigration.

Abstract: In this study, some Ni, Bi elements were added into low-Ag (less than 1%) Sn-Ag-Cu (SAC) solder. The effect of these additive elements on the solderability, intermetallic compounds (IMCs), and electromigration performance of low-Ag SAC (LASAC) solder were investigated. With the increase of Bi content in LASAC-0.05Ni-xBi (x=0, 2.0, 2.5, 3.0, 3.5, 4.0) solders, the peak melting point decreases while the wetting area of solder alloy increases. With the addition of Ni, the IMC between Cu pad and LASAC solder transforms from Cu6Sn5 to (Cu1-xNix)6Sn5 and the morphology of the IMC turns from bulk-like to needle-like. Either the addition of Bi or Ni will slow down the IMCs growth rate during high temperature storage aging (HTS) at 180°C and has a positive effect on electromigration performance of LASAC soldering.

Abstract: Temperature Coefficient of Resistance (TCR) is the important parameter in Electromigration Test of the metal reliability. The physical dimensions of the metallization can be affected by temperature. The coefficient of thermal expansion for a sample of the metallization can be used to approximate its change in volume given and a change in temperature. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material. TCR is a fractional change in resistance per unit change in temperature at a specified temperature. In order to get the most reliable metal lines, lower TCR value is needed. Normally lower TCR value can be obtained if the grain size of the metal line is smaller. In this study, two types of metal process flows which are known as hot and cold metal is evaluated using TCR measurement. The hot and cold metal process use the same source of AlSiCu but the preparation for deposition is a bit different in which the hot metal process used temperature setting of 300oC, while the cold metal process the temperature is set at 175oC. From the result it is found that the metallization sheet resistance is linearly increase with increasing temperature and the TCR value also decrease with smaller line widths. From the FIB micrograph picture it is found that lower process temperature will give smaller grain size and lower TCR value.

Abstract: An electro-thermo coupling finite element model is developed to investigate the electromigration and electro-thermo-mechanical effects on electronic packaging. Sn4.0Ag0.6Cu (SAC405) solder ball are commonly used on POP package in this research. Current density arising in the Copper trace above SAC405 solder ball implies the hot spot where results in an electromigration along the current direction. Finite element predictions reveal the peak electro-thermo-mechanical effective stress is located at the regions where electromigration potentially occurred. Current crowding, temperature distribution and electro-thermo induced effective stress distribution are predicted. A submodel scheme is applied for evaluation of equivalent life time of solder ball. Reliability analysis on electro-thermo-mechanical for SAC405 solder ball is evaluated.

Abstract: Both Al interconnects and flip-chip solder bumps were sensitive to high current. The failure mechanism of circuits interconnects would be more complicated if the current density in circuits was exceed the critical magnitudes of electromigration in both Al interconnects and solder bumps. The failure of circuit interconnects under different magnitudes of current density was studied and the interaction of electromigration in solder bumps and Al interconnects was discussed. The circuit interconnects of flip chip show three failure phenomena under high current density: voids in Al final metal, inter-diffusion of Al and SnPb, and melting of solder bumps. The voids in Al metal show the directional diffusion of Al atoms was mainly controlled by the electron wind fore. However the inter-diffusion of Al and SnPb demonstrated the electron wind force to Sn and Pb atoms would be ignored in contrast with chemical potential gradient or intrinsic stress. The flow of Sn and Pb atoms under high current density was in opposite direction with electron wind force and uniform with chemical potential gradient.

Abstract: It is strongly desired to operate SiC power devices at higher junction temperatures (Tj), but that often entails problems because they contain a variety of materials with thermal activity or weakness. An example of such troubles is the steep increase in resistance of the Al electrode in the source (or emitter) contact holes, caused by electromigration (EM). In this work, EM reliability of the contact hole in SiC power devices was evaluated for an improved Al electrode sandwiched between thin TaN layers. An estimated mean time to failure (MTTF) of approximately 3400 years was achieved under conditions of Tj = 300°C and J = 104 A/cm2.