Coverage and reliability improvement of copper metallization layer in through hole at BGA area during load board manufacture

Hu Z., Liu X., Ren T., Saeed H.A., Wang Q., Cui X., Huai K., Huang S., Xia Y., Fu K., Zhang J., Chen Y.

Abstract The advent of high frequency communication era presents new challenges for further development of dielectric polymer materials. In the field of communication, efficient signal transmission is critical. The lower the dielectric constant of the dielectric material used, the lower the signal delay and the higher the signal fidelity. The preparation of polymer materials with low dielectric constant or reduce the dielectric constant of polymer materials becomes a key research topic. Summarizing past progress and providing perspective, this paper primarily discusses the intrinsic low dielectric polymers, fluorine doped low dielectric polymers, and microporous low dielectric polymers, while predicting the research trend of low dielectric materials.

Agarwal R., Cheng P., Shah P., Wilkerson B., Swaminathan R., Wuu J., Mandalapu C.

Xiang C., Jin W., Huang D., Tran M.A., Guo J., Wan Y., Xie W., Kurczveil G., Netherton A.M., Liang D., Rong H., Bowers J.E.

The performance of silicon photonic components and integrated circuits has improved dramatically in recent years. As a key enabler, heterogeneous integration not only provides the optical gain which is absent from native Si substrates and enables complete photonic functionalities on chip, but also lays the foundation of versatile integrated photonic device performance engineering. This paper reviews recent progress of high-performance silicon photonics using heterogeneous integration, with emphasis on ultra-low-loss waveguides, single-wavelength lasers, comb lasers, and photonic integrated circuits including optical phased arrays for LiDAR and optical transceivers for datacenter interconnects.

Mina R., Jabbour C., Sakr G.E.

Analog integrated circuit design is widely considered a time-consuming task due to the acute dependence of analog performance on the transistors’ and passives’ dimensions. An important research effort has been conducted in the past decade to reduce the front-end design cycles of analog circuits by means of various automation approaches. On the other hand, the significant progress in high-performance computing hardware has made machine learning an attractive and accessible solution for everyone. The objectives of this paper were: (1) to provide a comprehensive overview of the existing state-of-the-art machine learning techniques used in analog circuit sizing and analyze their effectiveness in achieving the desired goals; (2) to point out the remaining open challenges, as well as the most relevant research directions to be explored. Finally, the different analog circuits on which machine learning techniques were applied are also presented and their results discussed from a circuit designer perspective.

Gharaibeh M.A.

Abstract This study aims to assess the effect of the solder joint array layouts, including full and peripheral designs, on the mechanical response and reliability of electronic packages subjected to shock and impact loadings. Linear and nonlinear finite element simulations using the global-local modeling technique are employed to perform the analysis. Several peripheral array configurations are considered and compared to the full array systems. The results showed that, for optimum electronic package designs in terms of reliability and cost, it is highly recommended to use peripheral packages having three or four rows of solder interconnects in electronic systems under shock and impact loadings.

Kyzioł L., Żuk D., Abramczyk N.

Abstract The purpose of the experiment was to determine the distribution of shear stresses in the measurement area of a natural and modified wood sample. Previous wood shear tests conducted on a typical Iosipescu specimen have shown that a complex stress state exists at the bottom of the notch. With transverse loading of the samples, flexure occurs and normal stresses arise from the bending moment and thus fibers are deformed. For the investigations oriented on shear, shear with stretching, and shear with compression, a special specimen was prepared which differed by notch geometry from a typical Iosipescu specimen. A new test machine is described in the article, which is equipped with special specimen holders to perform investigations in complex stress conditions. Crack patterns recorded for natural and modified wood are presented. For all tests, numerical finite element model simulations were performed to obtain stress distributions inside the specimens. The calculated stress distributions were visualized as contour line projections for natural and modified wood. Transverse shear strength values for the modified Iosipescu sample were found to exceed the magnitude of previously published ASTM D1037-87 test results. The test results proved that the strength properties of anisotropic materials in a complex state of stress can be assessed with great accuracy. This is very important in engineering applications.

Liu Q., Li D., Guan C.

Abstract During the production process of some copper clad laminate (CCL), the content of 3,3,5,7,7-pentamethyl-1,2,4-trioxepane in prepreg can affect the cross-linking and curing degree of resin directly, and thereby affect the properties of CCL. In this article, near-infrared (NIR) spectroscopy combined with partial least square regression using high performance liquid chromatography as a reference method were used for the determination of 3,3,5,7,7-pentamethyl-1,2,4-trioxepane in the CCL production progress. 160 spectra of prepreg samples randomly formed the calibration set, and 50 spectra of prepreg samples formed the validation set. The value of the root mean square error of calibration (w/w) and root mean square error of prediction (w/w) were 0.011% and 0.013% for 3,3,5,7,7-pentamethyl-1,2,4-trioxepane content (%, w/w), and the calculation and validation of the regression equation resulted in high correlation coefficients of 0.99 and 0.98, respectively. The scatter plot value of calibration set which was obtained from the root mean square error of cross-validation (w/w) was 0.015%, and the regression equation resulted in high correlation coefficient of 0.98. The results of the paired t-test revealed that there was no significant difference between NIR and HPLC method. Thus, the results obtained in this study reflect that NIR could be used as a rapid, accurate, and simultaneous technique to determine 3,3,5,7,7-pentamethyl-1,2,4-trioxepane content of prepreg in the production process.

Yu Y., Li B., Zhang Y., Zhang C.

Abstract In this study, the comprehensive performance and material properties of recycled aggregate concrete (RAC) under the coupled effect of salt-frost cycles were investigated to simulate the effect of complex environmental effects on the durability and deterioration of RAC. The tests on mass loss, relative dynamic modulus of elasticity (RDME), and compressive strength of RAC were conducted after 0, 25, 50, 75, and 100 standard salt-frost cycles. The results show that the mass loss, RDME, and compressive strength of RAC develop in a bad direction with the increase of the number of salt-frost cycles and the amount of recycled aggregate admixture. The concrete damage is particularly severe at more than 40% recycled aggregate admixture. This phenomenon is explained by the changes in the microscopic morphology, distribution of the pore structure, and functional groups of RAC.

Ashokkumar M., Thirumalaikumarasamy D., Sonar T., Deepak S., Vignesh P., Anbarasu M.

Abstract Cold spray process (CSP) is a thermal spray technology in which coating (10–40 µm) is formed in the solid state by the impingement of power particles with supersonic velocity (200–1,200 m/s2) on coupon employing compressed gas jet, below the melting point of coating powder. It is commonly referred as cold gas dynamic spray, high velocity powder deposition, kinetic spray and kinetic energy metallisation process. Using CSP, various engineering materials (metals, polymers and ceramics) and its composites can be deposited. It is unique and promising approach for obtaining surface coating and offers various technological benefits over thermal spray as kinetic energy is employed for deposition rather than thermal energy. This offers great benefits in additive manufacturing (AM) to develop a component denser, low oxide coating free of tensile residual stresses, and undesired chemical reactions compared to conventional AM and coating techniques. Cold spray additive manufacturing (CSAM) is the powerful and emerging technique in the field of AM to develop engineering components with improved performance covering broad range of functionalities of surface, subsurface and interfaces. There are few flaws in this technique; however, extensive research work is going in CSAM and repairing of components to meet the real-time applications. The main objective of this review article is to summarise the history, effect of process parameters on surface coating, research and development in CSP along with its implementation in AM, component repairing and biomedical, antimicrobial and electrical applications. A discussion on future trends in CSAM is also provided at the end part of this article.

Yang Y., Cheng S., Zhang Z., Yin M., Hou J.

Abstract The holes and defects in rock materials have a great impact on the mechanical properties and failure mechanism of rock, cracks often appear in the form of flat ellipses in natural rock mass, and the current research is still insufficient. For this purpose, based on the Particle Flow Code (PFC) of discrete element particle flow program, the numerical prefabricated fractured rock samples with the ratios of the long and short axes of the elliptical fractures being 5, 7.5, 10, 12.5, and 15 were simulated in order to obtain the strength and failure characteristics, stress concentration characteristics at tips of numerical rock samples in uniaxial compression test. The results of the numerical test simulation show that: (1) When the rock models with prefabricated elliptical crack were damaged, the initial cracks occurred at the end of the short axis of the elliptical crack, and penetrated up and down from the surface of the elliptical crack, the wing cracks occurred at both ends of the long axis, gradually formed a macro-crack, and the secondary cracks extended near the wing crack. (2) With the increase of the ratios a:b of long and short axes of the elliptical fracture, the strength and elastic modulus of the numerical rock samples gradually decreased, Poisson’s ratio gradually increased, and the total number of micro-cracks in the rock models decreased. (3) The numerical solutions of stress concentration factor k obtained by numerical simulations at the tip of the elliptical crack increased with the increase in the ratio of a:b; it was highly consistent with the variation law of the analytical solution of the stress concentration factor calculated by the theory of flat ellipse. The stress concentration is an important reason for failure of rock with elliptical cracks. Study on the crack tip will be very useful and significant.

Lv Z., Yang Z., Zhang J., Li X., Ji P., Zhou Q., Zhang X., Shi Y.

Abstract Based on the three-dimensional field of molten pool and twin-roll strip casting experiments, this work verified the cracking mechanism of the strip by establishing mathematical model and rolling experiments. The results showed that due to the instability of the thermophysical field of the molten pool and the inconsistency of kiss curve height, the newly solidified strip will undergo incompatible deformation through the rolling. The stress concentration will appear around the large reduction area and then form slip bands. When plastic strain exceeds the limit of the metal, the oblique cracks will appear in the slip bands periodically or completely penetrate the strip. In addition, tensile cracks could also be produced by incompatible deformation. Therefore, keeping the uniformity and stability of the thermal physical field in molten pool is the key factor to restrain cracks.

Kim J., Chekuri V.C., Rahman N.M., Dolatsara M.A., Torun H.M., Swaminathan M., Mukhopadhyay S., Lim S.K.

In this article, we present an effective methodology for co-design, co-analysis, and the system-level optimization of chiplet/interposer power delivery network (PDN) in 2.5-D integrated chip (IC) designs. In our methodology, we first generate a commercial-grade heterogeneous 2.5-D IC designs including full signal routing and power delivery. We then perform our PDN co-analysis in frequency and time domains on the entire PDN to evaluate various mechanisms added to our PDN designs. Based on our co-analysis results, we perform the system-level optimization on both interposer and chiplet PDNs with the stable performance of power delivery. Finally, we perform power, performance, and area (PPA) analysis and power integrity (PI) on our 2.5-D designs and discuss tradeoffs in chiplet and interposer levels due to PDN optimization. Our experiments show 27.17% improvement in the overall IR-drop in the optimized 2.5-D IC design by increasing the interposer PDN occupancy by 5.52% and inserting the additional PDN grids in chiplet designs. However, we also observe tradeoffs in terms of PPA and PI. By PDN optimization, the optimized design has an 11.6% increase of the total power, while the area of 2.5-D design remains the same. Moreover, from the perspective of PI, the tradeoffs are shown by 0.6% reduction of power efficiency, 32.6% higher output ripple, and 31.5% higher initial ringing because of an inductive behavior of interposer PDN in the optimized design.

Hunkel M.

Abstract Segregation is an unavoidable phenomenon in continuous or ingot casting of steel for thermodynamic reasons. If costly processes that explicitly reduce segregation are not carried out, the segregations remain until the final product. Therefore, an understanding of the development and effects of segregation along the entire process chain is necessary. The focus in this publication is on the treatment of segregations in low alloy steels. First, the characterisation of segregation is presented. An overview of the formation and development of segregations during primary shaping and forming processes is given. The focus is on segregation-related effects during heat treatment with regard to inhomogeneous microstructure and negative heat treatment results such as distortion or hardening cracks. In a short outlook, the influence of segregation on the component behaviour is described. ◼

Wanhill R.J., Stanzl-Tschegg S.E.

Abstract This paper results from mutual discussions on the review ‘When do small fatigue cracks propagate and when are they arrested?’ in Corrosion Reviews, 2019; 37(5): 397–418. These discussions have arisen from the two engineering paradigms characterizing our fatigue research: (i) an aerospace research and technology remit for metallic airframes, and (ii) a materials science research programme supporting a methodology for steam turbine low pressure (LP) blade operations. In our opinion, this paper is of interest for other investigators of metal fatigue with respect to design requirements, life predictions and assessments. In more detail, the paper considers the fatigue design methodologies for airframes and steam turbine LP blades. This includes short/small fatigue cracks, fatigue crack growth thresholds, high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF), and the relevance of environmental effects (corrosion and corrosion fatigue).

Kosarev A.A., Kalinkina A.A., Kruglikov S.S., Vagramyan T.A., Kasatkin V.E.

This article studies the effect of macro- and microdistribution factors on the uniformity of electroplated copper coatings in through-holes of printed circuit boards. A computer program has been developed for simulating the primary potential distribution field and for calculating the local current densities for a two-dimensional model of electrodes with arbitrary shapes and mutual arrangement. The cross-sectional profile of a through-hole with a channel width equal to the hole diameter was taken as the two-dimensional model. A calculation of the primary potential distribution field predicts that the current density in wide through-holes decreases significantly and electroplating in narrow holes is nearly blocked. As the diameter of a through-hole decreases, the macrothrowing ability decreases in accordance with the decrease in the Wagner number, while the nonuniformity of the copper deposit thickness inside the holes increases, as confirmed by micrographs of cross sections of samples obtained in the electrolyte with and without a set of additives. The latter comprised leveling agents based on polyalkylene glycols and nitrogen-containing heterocyclic compounds, along with brightening organic sulfur-containing additives. Analysis of data on the distribution of copper on the cross sections of samples treated in stagnant electrolytes and with stirring, other conditions being equal, reveals a significant effect of uneven microdistribution in narrow holes. Addition of the set of leveling and brightening compounds to the electrolyte provides a small positive leveling power, which makes it possible to obtain uniform smooth coatings without a local thickness decrease at the orifice. The noticeable increase in the copper layer thickness in the middle of narrow holes in the presence of additives observed under conditions of diffusion limitations cannot be explained solely in terms of the effect of primary and secondary distribution. The effect of the increase in d1/2 may be due to the depolarizing effect of the brightening sulfur-containing components of additives inside the holes.