Papers by Mohammed Genanu
AIP Publishing Showcase, 2024
This study aims to assess the mechanical and thermal characteristics of epoxy/aluminum and unsatu... more This study aims to assess the mechanical and thermal characteristics of epoxy/aluminum and unsaturated polyester/aluminum composite systems, using the formulations (1-x) EP + (x) Al microparticles and (1-x) UP + (x) Al microparticles, where x equals 0.00, 0.01, 0.03, and 0.05 wt%. Test specimens were created using an open mold-type die, and their impact strength, hardness, and thermal conductivity were experimentally examined. According to the results, epoxy/aluminum composites achieved their highest impact strength (15.63 KJ/m2) at 0.05 wt%, while the unsaturated polyester/aluminum composites achieved their highest impact strength (8.03 KJ/m2) at the same weight percentage. Moreover, the epoxy/aluminum composites exhibited superior impact strength compared to the unsaturated polyester/aluminum composites at the 0.05 wt% ratio.In terms of hardness, the epoxy/aluminum composites reached the highest Shore D value (78.6 H.NO.) at 0.05 wt%. On the other hand, the unsaturated polyester/aluminum composites displayed higher Shore D values (88.03 H.NO.) in the laboratory, with the 88.03 value being the highest for this type of composite, compared to 78.6 for the epoxy variant. La stly, the thermal conductivity (K) value increased in both epoxy/aluminum and unsaturated polyester/aluminum composites as the proportion of added aluminum powder grew.
EDFA Technical Articles
IBM engineers recently conducted a study to better understand and control the reliability of copp... more IBM engineers recently conducted a study to better understand and control the reliability of copper pillar solder joints in 2.5-D packages. Here they describe their approach and the results they obtained. They explain how they created test samples to evaluate different solder compositions, pillar geometries, and thermal histories and assess their effect on microstructure, precipitate morphology, intermetallic layer thickness, and shear strength. They also present thermal cycling test results comparing the performance of silicon and glass interposers.
International Symposium on Microelectronics
A 3-D packaging approach such as die stacking is an attractive way to package greater functionali... more A 3-D packaging approach such as die stacking is an attractive way to package greater functionality and performance into a smaller footprint, often at a reduced overall product cost. Achieving such 3-D integration can however place significant demands on the manufacturing process, often requiring substantial production expense to bond multiple die in a sequential manner. One alternative, potentially offering significant throughput, is the use of selective laser reflow to bond stacked die. This process produces a localized heating of the stacked die sufficient to produce soldered interconnects at the bonding interface but with very short exposure times that minimize the heating of other parts of the assembly and decrease the overall duration of the bonding process. The use of a commercial infrared (IR) laser reflow instrument for the sequential attachment of thin die into a 3-D stack was considered. The bonding technology under study consists of an infrared laser coupled with a custo...
2016 IEEE 66th Electronic Components and Technology Conference (ECTC), 2016
With the challenges of moving to 2.5/3D packaging structures, it has become imperative to improve... more With the challenges of moving to 2.5/3D packaging structures, it has become imperative to improve our understanding of the materials science of fine pitch Pb-free solder joints. The use of Cu pillars capped with thin layers of SnAg solder provides for tighter bump pitches reducing the chance of solder bridging at chip joining. However, changes in geometry, materials and processes associated with 2.5 D packaging create new materials challenges. The thinner solder regions mean that a larger volume fraction of joints is consumed by the formation of intermetallic compounds at the pillar/SnAg solder interface. The final concentration of Ag in the joint can vary, and the Ag3Sn precipitate morphology in the solder joint may change, directly affecting the reliability of the joint. This can occur through the formation of Ag3Sn plates, or simply because of different distributions of much smaller Ag3Sn precipitates. Or, the entire solder joint may be transformed into intermetallic compounds during assembly or operation of fine pitch joints. The presence of interposer materials with a different CTE compared to FR-4 laminates may also affect the lifetime of the package during drop/shock or thermal fatigue. In the current study, relations between processing, microstructure and reliability of assemblies enabled through Cu pillar/interposer technology were examined. The effects of solder cap composition, thickness and volume on microstructure of assemblies on Si and glass substrates were examined. Effects of multiple reflows on the microstructure of solder joints were also studied. Significant variation in Ag3Sn precipitate morphology was observed under nominally identical fabrication conditions. These were correlated with relatively large variations in mechanical behavior, for instance in measured values of shear strength. Large variations in Ag3Sn precipitate size and number were also observed with changes in composition and upon aging, as would be expected. Cu pillar assemblies revealed small, but continuous solder layers. After failure during ATC, cracks were found to have propagated through these continuous solder layers.
The desire for smaller, lighter and faster products drives the development of 2.5D/3D integration... more The desire for smaller, lighter and faster products drives the development of 2.5D/3D integration technologies that can utilize tens of thousands of connections per die. Micro copper (Cu) pillar geometries have been widely adopted because their small size and fine pitch provides high thermal conductivity, higher input/output (I/O) density and resistance to deleterious electromigration effects. In micro Cu-pillars, SnAg solder is electroplated on top of a Cu pillar. Because of the small volume of solder employed, intermetallic compounds comprise a significant fraction of the resulting solder joint, and very fine Ag3Sn precipitate morphologies can occur. Thus, the microstructure of SnAg solder/Cu pillar microstructures varies significantly from that of larger solder joints such as flip chip solder joints. Furthermore, 2.5D applications include interposers of distinctly different materials, such as Si or glass. The different properties of these materials such as coefficient of thermal ...
2017 IEEE 67th Electronic Components and Technology Conference (ECTC), 2017
The effect of the variation of processing parameters such as thermal history, or the composition ... more The effect of the variation of processing parameters such as thermal history, or the composition of Sn-Ag-Cu solder joints, on microstructure and reliability performance depends strongly on joint geometry, in particular length scale. The advent of 2.5/3D packaging technologies in microelectronics has further decreased joint length scales and changed interconnect aspect ratios to reduce I/O pitch. While fifty to one-hundred-micron diameter joints are becoming more common, the diameter of some SnAg based solder joints has been reduced to as little as ten microns, affecting the solidification microstructure and the formation of intermetallic compounds at solder/metallization interfaces. This study investigates these effects and correlates them with shear strength and reliability performance in accelerated thermal cycle test. Comparisons with results from solder joint studies at much larger length scales (ball grid array) are reported. Copper pillars having Sn caps with controlled varia...
Journal of Electronic Materials
The effects of reflow parameter values on the microstructure of SnAgCu/SnBiAg mixed assemblies we... more The effects of reflow parameter values on the microstructure of SnAgCu/SnBiAg mixed assemblies were examined. The variation of the volume fraction of the hypoeutectic SnBiAg phase with respect to the peak temperature during reflow, and the initial volumes of the SnAgCu and SnBiAg phases, was characterized. A simple theory was developed to predict the volume of the SnAgCu and SnBiAg phases after reflow, as a function of the peak temperature during reflow and the initial volume of the SnBiAg phase. This theory was based upon a one-dimensional Sn/eutectic SnBi mixed assembly. Concentration gradients in the hypoeutectic SnBiAg phase after reflow were characterized and compared to results from the Scheil equation.
2018 IEEE 68th Electronic Components and Technology Conference (ECTC), 2018
New applications and materials continue to pose challenges and opportunities for automated microe... more New applications and materials continue to pose challenges and opportunities for automated microelectronics manufacturing. Alternative approaches are becoming available but for most purposes the use of soldering in high volume applications still offer major advantages. However, the inability of many inexpensive materials to survive conventional mass reflow temperatures present a serious obstacle to this. One potential work-around still offering a relatively high throughput would be the use of selective laser reflow. This allows the local heating of solder joints and paste deposits for such a short time that other parts of the assembly are not heated nearly as much. Of course the properties of the resulting solder joints are somewhat different than typically achieved with mass reflow. An example of the use of a commercial infrared (IR) laser reflow instrument and its consequences in terms of solder joint properties was considered. Details including the impact of material properties a...
SMTA international2017 , 2017
Two extremes of reflow time scale for copper pillar flip chip solder joints were explored in this... more Two extremes of reflow time scale for copper pillar flip chip solder joints were explored in this study. Sn-2.5Ag solder capped pillars were joined to laminate substrates using either conventional forced convection reflow or the controlled impingement of a defocused infrared laser. The laser reflow joining process was accomplished with an order of magnitude reduction in time above liquidus and a similar increase in solidification cooling rate. The brief reflow time and rapid cooling of a laser impingement reflow necessarily affects all time and temperature dependent phenomena characteristic of reflowed molten solder. These include second phase precipitate dissolution, base metal (copper) dissolution, and the extent of surface wetting. This study examines the reflow dependent microstructural aspects of flip chip SnAg joints on samples of two different size scales, the first with copper pillars of 70μm diameter on 120μm pitch and the second with 23μm diameter pillars on a 40μm pitch. The length scale of Pb-free solder joints is known to affect the Sn grain solidification structure; Sn grain morphology will be noted across both reflow time and joint length scales. Sn grain morphology was further found to be dependent on the extent of surface wetting when such wetting circumvented the copper diffusion barrier layer. Microstructural analysis also will include a comparison of intermetallic structures formed; including the size and number density of second phase Ag 3 Sn precipitates in the joint and the morphology and thickness of the interfacial intermetallics formed on the pillar and substrate surfaces.
The desire for smaller, lighter and faster products drives the development of 2.5D/3D integration... more The desire for smaller, lighter and faster products drives the development of 2.5D/3D integration technologies that can utilize tens of thousands of connections per die. Micro copper (Cu) pillar geometries have been widely adopted because their small size and fine pitch provides high thermal conductivity, higher input/output (I/O) density and resistance to deleterious electromigration effects. In micro Cu-pillars, SnAg solder is electroplated on top of a Cu pillar. Because of the small volume of solder employed, intermetallic compounds comprise a significant fraction of the resulting solder joint, and very fine Ag 3 Sn precipitate morphologies can occur. Thus, the microstructure of SnAg solder/Cu pillar microstructures varies significantly from that of larger solder joints such as flip chip solder joints. Furthermore, 2.5D applications include interposers of distinctly different materials, such as Si or glass. The different properties of these materials such as coefficient of thermal expansion, affect the thermomechanical response of the package to temperature excursions and the lifetime of the package. Thus, behaviors of Cu pillar packages during Accelerated Thermal Cycling (ATC) were examined. Correlations between the shear strength and microstructure of Cu pillars were examined for different solder compositions, and for different aging times. Microstructure analysis (e.g. Ag 3 Sn precipitate morphology) was performed with both optical and scanning electron microscopy. The effects of thermal aging on the growth of intermetallic compounds (IMCs), the Ag 3 Sn precipitate morphology and on the mechanical properties of micro Cu pillar bumps were examined. The shear strength performance of micro Cu pillars with three different bump diameters (30µm, 50µm, and 100µm) was also evaluated. Results were considered in terms of variations in the precipitate morphology, and in terms of increases in the thicknesses of intermetallic layers at micro solder/substrate interfaces. ATC test results for two different interposers (Si and Glass with High CTE) will be discussed.
In this paper, the preparation of samples for testing in a manner manual configuration of the epo... more In this paper, the preparation of samples for testing in a manner manual configuration of the epoxy material as the basis of the staple food of the type of glass fiber woven roving. Been studied fatigue behavior of epoxy material and their complexes supported by breaking the glass fiber volumes of 30% and 40%. Examination was conducted in a manner is alternating bending, fatigue test results showed the effect of increasing of reinforcement on the fatigue behavior of the dry samples where it will increase the number of fatigue cycle until failure (fatigue life). But when the immersion kerosene samples will lead to a decrease of weight for the epoxy unreinforced and failure faster than the dry sample as well as in reinforcing by volume fraction 40% will decrease the weight and fail faster than the sample itself is dry, either at the rate of reinforcement volume fraction 30% will absorption occurs but without improvement in fatigue behavior. When you immerse the samples with gasoline (benzene) all the samples are reinforced and not will lose the weight initially and then re-absorption will increase weight, and the number of cycles until failure (fatigue life) of epoxy sample unreinforced less than the same sample is dry, as well as less than a sample immersion in kerosene and for all applied loads, as well as epoxy samples, are reinforced at both ratios of the volumetric fraction will still be less than if they were dry or immersed in kerosene than through decrease the value of applied loads on the two samples.
This paper includes the study of fatigue behavior for two types of polymer composites; epoxy resi... more This paper includes the study of fatigue behavior for two types of polymer composites; epoxy resin reinforced by chopped carbon fibers and unsaturated polyester resin reinforced by chopped carbon fibers (CCF) with different weight percentage (2.5%,5%,7.5%,10%,12.5%). Hand-lay up method was used to prepare sheets of composites on glass mould which were cutting according to the standard fatigue test. The fatigue test was carried out under alternate bending method, which made by applying sinusoidal wave using fixed displacement technique with two applied displacements (U=10mm, 15mm) and with fixed frequency 10Hz. The fatigue results(maximum stress, fatigue strength, fatigue limit and fatigue life)for EP-CCF and UPE-CCF composites were measured under two applied displacements 10 mm and 15 mm. Reinforcing by chopped carbon fibers reduces the brittle nature of epoxy and unsaturated polyester as their fatigue behavior enhanced. The fatigue results for UPE and its composites have higher values of maximum stress than for EP and its composites at two applied displacements. Increasing weight percentage of CCF has strong influence by increasing fatigue strength, fatigue limit and fatigue life for EP and UPE composites except the composites with 12.5% CCF, which subject to rapid failure at U equal to 15 mm. Finally it is found that EP composites at U=10 mm have better fatigue behavior, especially, fatigue limit and fatigue life over whole CCF percentage as UPE composites suffer more damages especially at high number of cycles. Ingeneral UPE composites suffer rapid damages more than EP composites at two applied displacements. Keywords : fatigue behavior , epoxy resin (EP) , unsaturated polyester resin (UPE), chopped carbon fiber (CCF), polymer composites.
Keywords fatigue behavior epoxy resin (EP) Hand-lay up method was used to prepare the samples mad... more Keywords fatigue behavior epoxy resin (EP) Hand-lay up method was used to prepare the samples made of epoxy (EP) as a matrix reinforced with chopped carbon fibers (CCF). The fatigue behavior of epoxy resin /chopped carbon fiber composites was studied with different weight percentage of chopped carbon fibers (2.5%,5%,7.5%,10%,12.5%). The fatigue test was carried out under alternate bending method, which was made by applying sinusoidal wave with constant displacement (15mm), stress ratio R=-1,and loading frequency 10Hz, which is believed to give a negligible temperature rise during the test. The results of the maximum stress, fatigue strength, fatigue limit and fatigue life of the tested composites are calculated from stress(S)-number of cycles(N) (S-N) curves. It was shown that increasing weight percentage of chopped carbon fibers increase the values of maximum stress for all composites, while the values of fatigue strength, fatigue limit and fatigue life increasing for all composites except the composite with reinforcing weight 12.5%, which was subjected to rapid failure (fracture). This failure could be due to the debonding of the chopped carbon fibers from the matrix epoxy.
Conference Presentations by Mohammed Genanu
— With the challenges of moving to 2.5/3D packaging structures, it has become imperative to impro... more — With the challenges of moving to 2.5/3D packaging structures, it has become imperative to improve our understanding of the materials science of fine pitch Pb-free solder joints. The use of Cu pillars capped with thin layers of SnAg solder provides for tighter bump pitches reducing the chance of solder bridging at chip joining. However, changes in geometry, materials and processes associated with 2.5 D packaging create new materials challenges. The thinner solder regions mean that a larger volume fraction of joints is consumed by the formation of intermetallic compounds at the pillar/SnAg solder interface. The final concentration of Ag in the joint can vary, and the Ag3Sn precipitate morphology in the solder joint may change, directly affecting the reliability of the joint. This can occur through the formation of Ag3Sn plates, or simply because of different distributions of much smaller Ag3Sn precipitates. Or, the entire solder joint may be transformed into intermetallic compounds during assembly or operation of fine pitch joints. The presence of interposer materials with a different CTE compared to FR-4 laminates may also affect the lifetime of the package during drop/shock or thermal fatigue. In the current study, relations between processing, microstructure and reliability of assemblies enabled through Cu pillar/interposer technology were examined. The effects of solder cap composition, thickness and volume on microstructure of assemblies on Si and glass substrates were examined. Effects of multiple reflows on the microstructure of solder joints were also studied. Significant variation in Ag3Sn precipitate morphology was observed under nominally identical fabrication conditions. These were correlated with relatively large variations in mechanical behavior, for instance in measured values of shear strength. Large variations in Ag3Sn precipitate size and number were also observed with changes in composition and upon aging, as would be expected. Cu pillar assemblies revealed small, but continuous solder layers. After failure during ATC, cracks were found to have propagated through these continuous solder layers.
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Papers by Mohammed Genanu
Conference Presentations by Mohammed Genanu