Sidewall Crack Research Articles

Die Crack Prevention and Detection in Advanced Packaging

Semiconductor manufacturers are continuously driving efforts to put more computing power and speed into less volume. At the same time, consumers are demanding devices with more functionality that integrate a variety of interconnected circuit types. The result has been an increasing reliance on advanced packaging technologies that use fab-like processes to integrate multiple chips and to provide the increased I/O capability required. The demand for higher performance electronics in smaller packages has led to the development of wafer level packaging (WLP), panel level packaging (PLP) and fan-out level packaging. The need for low cost, smaller packages with high density interconnects for cell phones and wearable devices has been leading the development of advanced packaging. All of these advanced packaging techniques involve stacking multiple chips in vertical directions. In DRAM memory packaging, there are as many as eight dies integrated vertically and the manufacturers are trying to keep the thickness of the die as minimal as possible to keep an overall thin package profile. Backside thinning of fully processed wafers has become a widely used technique in the industry. Typical final wafer thickness in the early 1990s was around 450µm but current wafers are usually thinner than 50µm. As the final wafer thickness is getting thinner, they are becoming more fragile and susceptible to cracks and chips. Chipping and cracks can cause near-term yield and long-term reliability problems. If a chip or crack is discovered during the final processes of advanced packaging, the overall final yield will be lower. If it is not discovered, the end device may not be reliable in the real world and fail for the consumer, a more costly consequence. As wafers became thinner, the industry started seeing sidewall cracks, inner cracks and micro cracks starting from the kerf or street area initiated from wafer sawing. These types of cracks can cause air bubbles around the cracks during the molding process in fan-out packaging and eventually lead to mold cracking which can lead to lower yields. It would be very beneficial if these types of cracks are detected early and the affected die removed. However, these types of cracks are happening underneath the die surface and are difficult to see with traditional bright field and dark field illuminations because they are underneath the top surface. Consumer tolerance for device failure is at an all-time low, as they demand more functionality and more convenience from their electronic devices. Wafer level packaging (WLP), panel level packaging (PLP) and fan-out level packaging advanced packaging techniques all involve extensive use of bumps and die thinning to establish electrical connections in vertical directions. Packaging these vertically integrated die requires the need to provide interlayer connections that are as small and reliable as the multilayer interconnect technologies used within the chip. This need for vertical connections has created a whole new class of technologies; advanced packaging; with a whole new lexicon of terms and acronyms: through-silicon vias (TSVs), redistribution layers (RDLs), bumps, pillars, nails, under bump metallization (UBM), wafer-level packaging (WLP), fan-in, fan-out, and many more. All of these technologies serve the purpose of providing reliable, electrically isolated, vertical connections, and most, at some point, involve the creation of a conductive; ump; protruding through an insulating layer to carry the signal to the next layer above or below. As more chips are integrated vertically, overall package thickness increased as well and the common ways to reduce the overall package thickness are by thinning chips or die and reducing bump sizes. As die or chips are getting thinner, they become more fragile and susceptible to cracks or chippings. Cracks or chips can reduce the final package yields or cause long term reliability issues in the consumer devices. This paper describes inspection challenges for cracks underneath the die surface and possible solutions to overcome the challenges.

Algorithm of Mask-region-based Convolution Neural Networks for Detection of Tire Sidewall Cracks

Algorithm of Mask-region-based Convolution Neural Networks for Detection of Tire Sidewall Cracks

A case study on the deformation and failure mechanism of a soft rock mining roadway in the Xin'Shang'Hai No. 1 coal mine, China

Mining roadways in soft rock are seriously deformed and damaged, which affects the normal production of the mine. Based on the Xin'Shang'Hai No. 1 Coal Mine project, a true 3D physical model test was carried out to obtain the deformation evolution and failure features of the mining roadway. The results show that the strata movement of the panel drives the surrounding rock of the mining roadway to deform toward the center; the net size of the roadway near the longwall face decreases by 48.3%. The convergence of soft rock mining roadways can be divided into four phases, and the average convergence rate of a fast phase is 3.1 times that of a slow phase. The evolution of roadway failure is deformation accumulation → sidewall cracking → lining spalling → coal sidewall breaking → floor heave → bolt (cable) failure → full section deformation. Coal sidewall failure is an important turning point of mining stress-induced roadway failure. The extension of the broken area into the rock leads to the failure of the coal seam between the roof and floor and then induces the overall instability of the roadway. The radial deformation and stress evolution of the mining roadway are analyzed by numerical simulation, and the model test results are verified. The mining roadway in soft rock shows full section convergence characteristics under the stress of mining. Finally, countermeasures are proposed according to the failure mechanism to provide a reference for similar roadways.

Demonstration application of microbial self-healing concrete in sidewall of underground engineering: A case study

There are many laboratory researches for microbial self-healing concrete (MSC) but few engineering applications. Demonstration application is an essential link from laboratory to practical engineering. This paper describes a demonstration application case of MSC on the sidewall of an underground engineering, aiming to provide practical experience for the large-scale application of MSC. Firstly, microbial healing agent (MHA) with core-shell structure produced using automatic equipment, and laboratory tests were carried out to evaluate the effects of MHA on concrete performance. Then, the feeding method of MHA in concrete mixing station was studied. Finally, the MSC’s application effect were studied through embedded sensor and field monitoring. Results show that MHA has no negative effect on concrete properties and does not affect engineering use. Using an external cylinder to deliver MHA can ensure the feeding effect and safe production. Compared with ordinary sidewall, MHA can effectively heal cracks and reduce the number of cracks and the average length, width, and depth. This paper can provide a good demonstration for the popularization and application of MSC and a new technical scheme for the prevention and treatment of sidewall cracks in underground engineering.

An application of quality tools to improve the tyre remanufacturing process

The tyre remanufacturing industries are facing quality and performance issues of the remanufactured tyres as they have developed their own tyre retreading methods due to the lack of standardized retreading process guidelines. This study focuses on identifying the challenges of the tyre remanufacturing process, highlighting various defects in retread tyres and their causes so that the challenges could be mitigated and the quality and performance of the tyres could be improved. To achieve the objectives of the study, the quality tools including fishbone diagram and Pareto chart has been used. For the above analysis, the data has been collected through multiple field visits and semi-structured interviews. The findings of the study indicate that organizations can improve the utilization of worn-out tyres by identifying tyre retreading defects and their causes and by implementing corrective actions at different stages in the tyre remanufacturing. According to cause-and-effect analysis, the defects found are failure of tread due to lack of standard tread joint method, side bulge generation due to sidewall degrading, and failure of the buffer layer due to tread and sidewall crack. Besides, a few recommendations are made for tyre remanufacturing to increase productivity and minimize the defects generation in retreaded tyres.

Failure behavior of horseshoe-shaped tunnel in hard rock under high stress: Phenomenon and mechanisms

A particle flow code (PFC) was first applied to examining the mechanical response of a horseshoe-shaped opening in prismatic rock models under biaxial compression. Next, an improved complex variable method was proposed to derive the stress distribution around the opening. Lastly, a case study of tunnel failure caused by rock burst in Jinping II Hydropower Station was further analyzed and discussed. The results manifest that a total of four types of cracks occur around the opening under low lateral confining stress, namely, the primary-tensile cracks on the roof-floor, sidewall cracks on the sidewalls, secondary-tensile cracks on the corners and shear cracks along the diagonals. As the confining stress increases, the tensile cracks gradually disappear whilst the spalling failure becomes severe. Overall, the failure phenomenon of the modelled tunnel agrees well with that of the practical headrace tunnel, and the crack initiation mechanisms can be clearly clarified by the analytical stress distribution.

A Study of Acoustic Emission and Damage Evolution of Limestone under Different Stress Paths and Confining Pressures

Buried depth is an important factor affecting the deformation and failure of gob surrounding rock. Basing on triaxial compression unloading test and acoustic emission (AE) of limestone under three different initial confining pressures (5 MPa, 10 MPa, and 20 MPa) and three different stress paths, we analyzed the deformation and failure characteristics and energy releasing process of the virgin rock, the gob overburden rock, and the gob sidewall rock with different buried depths (within 1000 m). The results showed that, with the increase of buried depth, the shear fracture mainly propagated and the failure mode of the gob sidewall rock changed from brittleness to plasticity; however, the gob overburden rock was all brittle failure. Compared with shallow buried depths, the energy releasing triggered by confining pressure reduction in deep buried depths was more concentrated and intense. Under the background of deep buried depths, the peak strength and residual strength of the gob sidewall rock were the lowest, and the damage variable was the largest. We proposed that the first “acute phase” of AE can be wielded as the precursor information of the gob sidewall rock failure and crack propagation of hydraulic fracturing. The findings of the study are beneficial for the disaster prevention and control of deep mining in mountainous area, as well as fracturing evaluation.

Investigation of design and performance improvements on solid resilient tires through numerical simulation

Solid tires are often utilized to bear excessive loads. Therefore, sidewall cracks and internal heat build-up affect their durability more significantly. It is a challenge to minimize these factors and improve tire performance while maintaining the functionality of the solid tire. Moreover, there are no specific standard guidelines for modifying the solid tire design to achieve this objective. This study proposes several design and performance improvements to the solid resilient tire and investigates the performance of these modified designs using the Finite Element (FE) method under static and dynamic conditions. For these FE simulations, suitable hyperelastic models are obtained using curve fitting combined with three standard error measures. The results show that the Mooney-Rivlin, Ogden, and Yeoh material models show good agreement with experimental data for modelling the base, cushion, and tread layers of the tire, respectively. The developed FE models are validated using experimental data obtained from a leading tire manufacturing company in Sri Lanka. The validated model is used to develop and analyse two distinct tire models which have two different cavity geometries (circular and elliptical) in their cushion layers to minimize heat build-up and sidewall cracks. The tire reinforcements are also rearranged to further improve the performance of the models. The introduction of cavities helps to reduce strain energy dissipation and to increase the dissipation of internal heat by convection. Furthermore, the stress intensity on the side walls is also reduced, thereby minimizing sidewall cracks. Numerical experiments show that the modified designs have a lower strain energy density, lower stress concentration, and less material utilization when compared to the basic tire design.

Application of Anisotropic Ductile Fracture Model for Prediction of Diagonal Cracks in Outer Rim of Flange-Shaped Parts

Inclined rotary forming (IRF) combines bending and axial compression with rotation and is employed for forming flange shaft-structured parts from round rod billets. Although the forming load is smaller than that in conventional processes, cracks may develop during this process. However, it is difficult to predict the onset of cracks using conventional ductile fracture prediction equations. In this paper, the ductile fractures were predicted using the anisotropic ductile damage equations that the present authors previously developed. The proposed equation was expressed as a second-rank tensor resulting from the product of the stress tensor and the strain increment tensor. Referring to previously published results on the compression of cylindrical specimens, the difference between diagonal and longitudinal sidewall cracks was assumed by considering the anisotropy of ductile damage. The proposed equation was then applied to the IRF process, where diagonal cracks developed at the outer rim of the flange. Consequently, it was found that the proposed anisotropic damage model can predict the onset of diagonal cracks on the outer rim and the effect of the lubrication condition on the onset of these cracks.

Improve Chip Side Wall Crack Issue in Nanometer Packing Process of Semiconductor

The chip side wall crack of semiconductor nanometer packaging process has always been an important technological problem that the global semiconductor packaging industry needs to overcome. This research has helped the world's biggest semiconductor package factory to improve the chip side wall crack issue faced by nanometer wafer packaging process, thus enhancing its yield rate. After analyzing the abnormality of nanometer wafer packaging process, this research team found that the chip side wall crack problem was caused by a poor laser waveform during the laser cutting process, resulting in debris along the chip side wall. Subsequently, as the diamond cutter cuts into the chip in the following process, the cutter impacts the debris which then impacts the side wall resulting in a side wall crack. The Teoriya Resheniya Izobreatatelskikh Zadatch (TRIZ) analysis was used to deduce a suitable improvement method. After applying the TRIZ analysis, this research team confirmed that by modifying the laser equipment to create a more uniform laser waveform, the diamond cutter was able to achieve a clean cut of the chip without impacting debris and thus significantly decreased the chip side wall crack occurrences. The shipment yield rate was increased from 92.8% to 99.61% as a result of the team's modifications.

A new monitoring method for overlying strata failure height in Neogene laterite caused by underground coal mining

Determination of the overlying strata failure height, that is, water flowing fractured zone height (WFFZH), is critical to underwater coal mining, especially in the fragile geo-environment areas. Due to the property discrepancy of rock and soil, WFFZH penetrating the clay layer in the Jurassic coalfield cannot be accurately determined by conventional measurement method, a new formation micro-scanner image (FMI) method was presented and verified in the paper. Taking the N1208 coalface in the Shennan mining area, Shaanxi, China, as a case study, FMI based field test for monitoring WFFZH was carried out firstly. The scanning results show that subtle changes of drilling sidewall cracks could be presented intuitively in FMI scanning image, and the WFFZH was be determined as 145.15 m. Secondly, the whole evolutionary process of WFFZH is simulated using UDEC, whose maximum height of WFFZ is calculated as 147.0 m. Comparison results between on-site measurement and numerical simulation suggest that FMI technology is applicable to monitor the WFFZH in laterite layer. Thirdly, in order to illustrate the discrepancies in WFFZH developed in laterite and bedrock, a comparative numerical simulation tests results show that laterite layer has an inhibitory effect on WFFZH.

Advanced Die Saw Technology for WLCSP Reliability Enhancement

Abstract As consumer and portable devices get thinner and more functionality. Chips which are made by less than 28 nm node wafer with extreme Low-k (ELK) inter metal dielectric material is a trend in order to contain more transistors and to lower power consumption. However, side wall crack (SWC) for WLCSP is one of the major challenges since ELK layer getting brittle. Laser grooving is applied to remove metal before blade saw, but the high temperature during laser grooving usually easily generates HAZ (heat-affected zone) which can induce stress concentration and lower chip strength. The laser ablation also leaves metal-silicon residue (or recast) from the re-deposition of silicon to the groove and surrounding areas. Therefore, SWC (sidewall crack) is a huge potential risk waiting to happen after pick and place, during shipment and during SMT process. In the industry, HAZ size and SWC rate could be reduced by adjusting process parameters, or by exploring new alternatives to eliminate HAZ and silicon recast is one of driving factors of this paper. In this study, plasma etching was applied as surface treatment on the scribe line after laser grooving process with ELK wafer. Plasma could etch HAZ and recast area and expected to increase chip strength and reduce SWC rate. Plasma applied with various process time and power, and different types of mask coating materials were studied. Different plasma gases and effectiveness will be discussed. Conventional blade dicing process will be compared to different plasma etching conditions for mechanical properties of die using 3-point bending test to check die strength, and SEM and OM to verify quality of sidewall of the die. Finally drop test was performed to confirm the reliability enhancement.

Experimental simulation and investigation of spalling failure of rectangular tunnel under different three-dimensional stress states

Spalling (or slabbing) in the sidewalls of deep rectangular tunnels is a type of rock failure phenomenon under the three-dimensional stress environment, which often occurs on the surrounding rocks after the tunnel face excavation is completed and has a significant impact on the safety of construction and support. In order to investigate the spalling process in deep rectangular excavated tunnels under three-dimensional stress, a granite material was firstly processed into cubic specimens (100 mm × 100 mm × 100 mm) with prefabricated rectangular holes (40 mm × 40 mm). Simulation experiments were performed using a rock true-triaxial electro-hydraulic servo mutagenesis testing system under four different initial stress states. Meanwhile, a wireless micro-camera was used to record and monitor the damage process on the sidewalls of the rectangular tunnel in real time. The results showed that under the four stress conditions, an evident spalling failure occurred on the entire sidewalls of the rectangular hole. It was observed that the spalling-damaged zone gradually developed toward the deep part of the hole in a horizontal direction. Finally, it formed a penetrating symmetric arc-shaped groove along the axial direction, whereas the roof and bottom slab remained stable. The spalling failure process of the sidewalls had four stages: the calm period, particle ejection at the upper and lower shoulders, sidewall crack propagation, and crack penetration spalling failure. Compared with the dynamic failure (rockburst) of a circular tunnel under the same three-dimensional high stress conditions, the spalling failure of the rectangular tunnel sidewalls was of the static failure mode. Under the three-dimensional stress condition, the radial stress had a greater effect on the spalling failure than the axial stress, by increasing the radial stress can be significantly reduced the degree of spalling failure and effectively improved the stability of the surroundings.

Field and laboratory study of cracking and safety of secondary lining for an existing highway tunnel in loess ground

Lining cracking is a common distress for most existing highway tunnels in loess ground, and the development of such distress will directly affect the operation and service life of the tunnel. This paper studied the deformation evolution laws, cracking mechanism and failure process of the secondary lining for an existing highway tunnel in loess ground by carrying out field investigations and laboratory model tests. To simulate the field loading conditions more realistically, a 1: 10 large-scale test platform was developed and the loads acting on the lining model were determined according to the field measured pressure data. The statistical analysis of field tunnel distress indicates that the vault cracks more seriously than the sidewalls. The model test results show that the deformation and failure process of lining structure can be divided into three stages with two dividing points of vault cracking and inverted arch cracking. The intrados of vault and extrados of arch foot crack by tension, whereas the intrados of sidewall cracks owing to the high localized compression. The vault cracks first and exhibits the most serious cracking. Moreover, critical cracking zone is formed in vault, which finally makes the entire structure lose its load carrying capacity. Test results were compared with the characterization of field tunnel distress to validate their reliability, and conclusions regarding the safety assessment of studied tunnel sections were developed based on the comparison. The methods and findings of this study can serve as useful references for optimal design and long-term safety of tunnel structures.

Cause investigation of side-wall cracking in an operational tunnel

The underground environment is extremely complex and variable, which is one of the main factors affecting the safety of the structure. This paper presents a case study of investigating side-wall crackings in existing tunnels, in which the changes of structure's stress state induced by geological changes is investigated by means of field observation, in-situ test and numerical analysis. This work demonstrates that the side-wall cracking is significantly influenced by the softening of mudstone. The softening can not only reduce the bearing capacity of bedrock under tunnel, but also enhance the squeezing action of the surrounding rock on the structure, which the tunnel lining without invert cannot resist. Moreover, the treatment measure based on the principal cause is proposed and its effectiveness is demonstrated by numerical analysis.

Durability prediction of an ultra-large mining truck tire using an enhanced finite element method

Ultra-class mining trucks used for material haulage in rugged surface mining terrains experience premature tire fatigue failure in operation. Typical failures include belt edge separation, ply turn-up separation, and tread base and sidewall cracking. The use of reinforcing fillers and processing aids in tire compounds result in the formation of microstructural in-homogeneities in the compounds. This article presents an application of the critical plane analysis technique for predicting the fatigue life of the belt package of an ultra-large mining truck (CAT 795F) tire of size 56/80R63 in a surface coal mine. Experimental data obtained from extracted specimens (sidewall, tread, and belt edge region) of the tire are used to characterize the stress–strain and fatigue behavior of the modeled tire. The tire’s duty cycle stresses and strains were obtained from finite element analysis of the rolling tire in Abaqus. Fatigue life calculations were performed in the rubber fatigue solver Endurica CL. Effects of inflation pressure, tire speed, and axle load on the fatigue life of the belt package under strain-crystallizing and non-crystallizing conditions of the belt compound are discussed. Specifically, the results show the belt edges to be critical regarding crack nucleation.

Water droplet erosion behaviour of Ti–6Al–4V and mechanisms of material damage at the early and advanced stages

In this study, the water droplet erosion (WDE) behaviour of Ti–6Al–4V and mechanisms of material damage were investigated. The WDE test was conducted in an advanced rig in accordance with the ASTM G73 standard. The influence of impact speed between 150 and 350m/s on the WDE behaviour was explored and the cumulative mass losses versus the exposure time/number of impingements were plotted. It was observed that the higher the impact speed the faster the erosion initiation time and greater the maximum erosion rate (ERmax). ERmax was also found to be related to the impact speed with an exponent of 9.9 in a log–log scale. SEM images showed that the early stages of erosion damage were mainly limited to the formation of microcracks, asperities and isolated pits of irregular shapes. It was found that the most profound mode of material removal during the advanced stage of water droplet erosion was hydraulic penetration. Sub-surface, side wall cracking and material folding/upheaving were also features observed.

Non-Structural Cracking Analysis of Early Age of Basement Structure Based on Field Monitoring

Cracking of basement structure are common problems in civil building, so it’s most import and difficult to inhibiting cracking of building structures. In this paper, real-time continuous monitoring data of strain and temperature were obtained by embedding sensors in practical engineering, including slab and sidewall of reinforcement concrete, while ambient conditions were monitored to assess their effects. The cracking mechanism of such kind of structure was analyzed based on the investigation and monitoring data. The results show that sidewall is easier to crack than slab for basement structures of civil building, therefore, sidewall cracking of basement structure is the most difficult and key point to inhibit cracking. The measures adopted in this project can effectively reduce crack risk of structure. At the same time, the measured data can provide useful reference to control crack for similar projects and research, and they can also be used to verify the numerical results.

Off-axis Crashworthiness Characteristic of Woven Glass/Epoxy Composite Box Structures

This study investigates the influence of off-axis loading on the fracture mechanism and specific energy absorption (SEA) of glass/epoxy twill/weave composite box structures. In this regard, the off-axis angles of 5°, 10°, 20°, and 30° of loading direction with respect to the composite box axis is studied experimentally under quasi-static crushing process. At the off-axis angle of 5°, the crushing process behavior is similar to that of the axial crushing and fracture mechanisms, such as bundle fracture and interlaminar crack propagation in Mode-II are observed. These are characteristic of brittle fracture crushing mode. For crushing at an off-axis angle of 10°, additional interwall crack propagation at one side of the box is also found. This increases the energy absorbing capability of glass/epoxy composite box at this angle. The sidewall crack is a mixed-mode crack. To characterize this crack, the mixed-mode interlaminar fracture toughness, G I/IIC, is measured using asymmetric double cantilever beam (ADCB) test method. For other angles, the non-symmetrical fracture mechanisms are found at four sides of the composite boxes. The arriving of sustained crushing stage is delayed by increasing the off-axis crushing angle. Owing to this fact, the energy absorbing capability is reduced by increasing the off-axis loading angle. An analytical solution is proposed to predict the mean force of axial crushing in brittle fracture crushing mode. The off-axis crushing process of composite boxes is also simulated by finite element software LS-DYNA and the results are verified with the relevant experimental results.

Dicing Laminated Wafer for QFN 3D Stacked Die Packaging

Nowadays, die attach film (DAF) gaining popularity in microelectronic packaging as integral part in facilitating the growth of wafer level packaging and stacked die packaging. DAF applied to the backside of wafers prior to saw have many advantages, such as the elimination of the epoxy dispensed process step and the reduction of epoxy related failure mode. However, the dicing process for DAF wafer usually associated with sidewall chipping, DAF whiskering and crack that will affect reliability of Quad Flat Non-Leaded (QFN) stacked die. Blade properties and characteristics are the crucial factor in analyzing the DAF dicing results. In this paper, we evaluate the blade characteristics before and after DAF wafer dicing process for our stacked die packaging. The qualitative measure by means of the Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) analysis were performed in order to understand the lamination and dulling effect on blade surface. The obtained results showed that sawing polymeric material such as wafer laminated with DAF induces lamination of polymeric material onto the blade surface and reduce blade cutting edge. As a result, reduce the quality of DAF dicing process.