Failure analysis and stress simulation in small multichip BGAs

Improved reliability in small multichip ball grid arrays

FeNi alloy is considered a possible substitute for Cu as under bump metallization (UBM) in wafer level package (WLP) since it forms very thin intermetallic compound (IMC) layer with Pb-free solder in the reflow process. In this paper, WLPs with FeNi and Cu UBM were fabricated and their board level reliabilities were studied comparatively. The WLP samples assembled on the printed circuit board (PCB) were subjected to temperature cycling and drop tests according to JEDEC standards. The results showed that the reliability of WLP with FeNi UBM was a little lower than that with Cu UBM. The main failure modes for both FeNi and Cu UBM samples in temperature cycling test were the crack in IMC or solder ball on PCB side. And detachments between UBM and the redistribution layer (RDL) were also observed in Cu UBM WLPs. In drop test, the crack of RDL was found in all failed FeNi UBM samples and part of Cu UBM ones, and the primary failure mode in Cu UBM samples was the crack of IMC on PCB side. In addition, the finite element analysis (FEA) was carried out to further understand the difference of the failure modes between the FeNi UBM samples and the Cu UBM samples. The high stress was observed around the UBM and the pad on PCB in the temperature cycling model. And the maximum stress appeared on the RDL in the drop simulation, which was obviously larger than that on the pad. The FEA results showed that the introduction of FeNi UBM increased the stress levels both in temperature cycling and drop tests. Thus, the FeNi alloy cannot simply replace Cu as UBM in WLP without further package structural optimization.

The bimodular femoral neck implant (modularity in the neck section and prosthetic head) offers several implant advantages to the surgeon performing THAs, however, there have been reports of failure of bimodular femoral implants involving neck fractures or adverse tissue reaction to metal debris. We aimed to assess the results of the bimodular implants used in the THAs we performed. We asked: (1) What is the survivorship of the PROFEMUR(®) bimodular femoral neck stems? (2) What are the modes of failure of this bimodular femoral neck implant? (3) What are the major risk factors for the major modes of failure of this device? Between 2003 and 2009, we used one family of bimodular femoral neck stems for all primary THAs (PROFEMUR(®) Z and PROFEMUR(®) E). During this period, 277 THAs (in 242 patients) were performed with these implants. One hundred seventy were done with the bimodular PROFEMUR(®) E (all are accounted for here), and when that implant was suspected of having a high risk of failure, the bimodular PROFEMUR(®) Z was used instead. One hundred seven THAs were performed using this implant (all are accounted for in this study). All bearing combinations, including metal-on-metal, metal-on-polyethylene, and ceramic-on-ceramic, are included here. Data for the cohort included patient demographics, BMI, implant dimensions, type of articular surface, length of followup, and C-reactive protein serum level. We assessed survivorship of the two stems using Kaplan-Meier curves and determined the frequency of the different modes of stem failure. For each of the major modes of failure, we performed binary logistic regression to identify associated risk factors. Survivorship of the stems, using aseptic revision as the endpoint, was 85% for the patients with the PROFEMUR(®) E stems with a mean followup of 50 months (range, 1-125 months) and 85% for the PROFEMUR(®) Z with a mean followup of 50 months (range, 1-125 months)(95% CI, 74-87 months). The most common modes of failure were loosening (9% for the PROFEMUR(®) E), neck fracture (6% for the PROFEMUR(®) Z and 0.6% for the PROFEMUR(®) E), metallosis (1%), and periprosthetic fracture (1%). Only the bimodular PROFEMUR(®) E was associated with femoral stem loosening (odds ratio [OR] =1.1; 95% CI, 1.04-1.140; p = 0.032). Larger head (OR = 3.2; 95% CI, 0.7-14; p = 0.096), BMI (OR = 1.19; 95% CI, 1-1.4; p = 0.038) and total offset (OR = 1.83; 95% CI, 1.13-2.9; p = 0.039) were associated with neck fracture. Bimodular neck junctions may be potentiated by long neck lengths, greater offset, and larger head diameters. These factors may contribute to bimodular neck failure by creating a larger moment about the neck's insertion in the stem. The PROFEMUR(®) E implant is associated with high periprosthetic loosening. Based on our experience we cannot recommend the use of bimodular femoral neck implants. Level III, therapeutic study.

Column-wall failure mode of steel moment connection with inner diaphragm and catenary mechanism

The purpose of this work is to predict the failure modes of single lap composite bonded joints subjected to low energy impact loading using finite element analysis. Experimental data were collected during mechanical tests by impacting the specimen using a drop test tower. Maximum impact induced force and dissipated energy for each specimen were measured. Finite element simulations were carried out in Abaqus/Explicit using two damage models. The first damage model accounts for delamination failure modes by using a de-cohesive contact logic. The second damage model accounts for in-plane failure modes using maximum stress criteria and continuum damage mechanics. These models enable the prediction of inter and intra-laminar failure modes. The predicted impact force, displacement and damage pattern were found to be in good correlation with tests and thermographic inspections.

In this paper, failure analysis of an unmanned aerial vehicle (UAV) has been conducted through failure mode and effects analysis (FMEA) and finite element (FE) simulation. For FMEA, a system is broken down into subsystems, and possible failures are considered for each subsystem. Each failure is then ranked in 3 categories: severity, occurrence, and difficulty of detection. Each category has 1 of 5 ranks: very low, low, moderate, high, and very high. Since these ranks are linguistic variables that cannot be properly assigned a definitely value, fuzzy logic is applied. Using a membership function and a defuzzification formula, the variables are defuzzified. Grey relational analysis is applied to factor in the relationship between the variables. With these methods applied, the battery failure and rotor arm failure (including motors, ESC & arm structure) were found to be the most critical failures followed by avionics failure and structural failure. For the FE simulation, a 3D model is created. The stress distribution and fatigue life of fuselage are simulated by using the commercial software Comsol. The fuselage was made of Al 7076 T6 with an ultimate tensile strength of 572 MPa. The stress distribution at different loads (5 kg, 50 kg & 75 kg) are simulated. According to the simulation results, the maximum stress occurs at the corner of the fuselage. The fatigue life under different loads were also simulated. The potential failure mode and risk level analysis enables the identification of critical component and prediction of system failures. With FE simulation, the limit of the structure is simulated. Maximum load the structure can support is determined, the simulation of fatigue life cycles enables the prediction of structure failures.

Continued standards in reliability and shorter time to market have resulted in an increased focus on reliability modeling and correlation to shorten robust device development. One of the most time consuming and mechanically stressful reliability tests to qualify a product is Temperature Cycling (TC). In plastic packages with exposed pads to be connected to a printed circuit board, a common failure mode in TC test is die pad delamination due to coefficient of thermal expansion mismatches within the package. Thermal Shock (TS) reliability test is similar to TC with the advantage of being much faster to execute. In this study, die pad delamination is correlated for TS and TC using three test vehicles. A scanning acoustic microscopy based delamination extraction approach is described, and a Finite Element Analysis is used to develop a predictive TC thermo-mechanical model.

Failure physics of integrated circuits — A review

Failure analysis and countermeasures of a tunnel constructed in loose granular stratum by shallow tunnelling method

A methodology for predicting sites and modes of thermomechanical failure in IC and MEMS packages is developed. Singular stress fields around several stress concentration locations in a typical plastic-encapsulated IC package are calculated using special variable-order singular boundary elements and the singular value decomposition method. The strain energy density distributions around all the stress concentration locations are then obtained from the singular stress fields and compared. The most likely failure site as the temperature of the package is raised is then determined as well as the likely modes of failure, i.e. interfacial delamination or cracking of mold compound.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Failure analysis (FA) is a basic and effective method to obtain the physical and failure information of electronic components and circuits. Most of these information can provide many useful evidences for prognostic and system health management (PHM) of electronic products. To obtain these information, many failure analysis techniques are used. This paper focuses on analyzing the relationship between FA techniques and PHM system. To test and verify the availability of the relationship between FA techniques and PHM system, a failure analysis case of an Intelligent Power Module (IPM) is used to study the relationship. This IPM contains six insulated gate bipolar transistors (IGBTs) and there are obvious burnout indications on most of them after failure. With the process of failure analysis, the key information, such as component's structure, sensitive parameters are identified. These results persuasively prove that FA techniques can provide much information to PHM system, including PoF and data-driven methods.

A finite element analysis (FEA) model is established to investigate the concrete-encased concrete-filled steel tubular (CFST) column to reinforced concrete (RC) beam joints under cyclic loading. The feasibility of the FEA model is verified by a set of test results, consisting of the failure modes, the exposed view of connections, the crack distributions and development, and the hysteretic relationships. The full-range analysis is conducted to investigate the stress and strain development process in the composite joint by using this FEA model. The internal force distributions of different components, as well as the deformation distributions, are analyzed under different failure modes. The proposed connections are investigated under dimensional and material parameters, and the proper constructional details of the connections are recommended. Parameters of the beam-column joints, including material strength, confinement factor, reinforcement ratio, diameter of steel tube to sectional width ratio, beam to column linear bending stiffness ratio and beam shear span ratio are evaluated. Furthermore, the key parameters affecting the failure modes and the corresponding parameters ranges are proposed in this paper.

Damage in composite laminates evolves through complex interactions of different failure modes, influenced by load type, environment, and initial damage, such as from transverse impact. This paper investigates damage growth in cross-ply polymeric matrix laminates under tensile load, focusing on three primary failure modes: transverse matrix cracks, delaminations, and fiber breaks in the primary loadbearing 0-degree laminae. Acoustic emission (AE) techniques can monitor and quantify damage in real time, provided the signals from these failure modes can be distinguished. However, directly observing crack growth and related AE signals is challenging, making numerical simulations a useful alternative. AE signals generated by the three failure modes were simulated using modified step impulses of appropriate durations based on incremental crack growth. Linear elastic finite element analysis (FEA) was applied to model the AE signal propagating as Lamb waves. Experimental attenuation data were used to modify the simulated AE waveforms by designing arbitrary magnitude response filters. The propagating waves can be detected as surface displacements or surface strains depending upon the type of sensor employed. This paper presents the signals corresponding to surface strains measured by surface-bonded piezoelectric sensors. Fiber break events showed higher-order Lamb wave modes with frequencies over 2 MHz, while matrix cracks primarily exhibited the fundamental S0 and A0 modes with frequencies ranging up to 650 kHz, with delaminations having a dominant A0 mode and frequency content less than 250 kHz. The amplitude and frequency content of signals from these failure modes are seen to change significantly with source–sensor distance, hence requiring an array of dense sensors to acquire the signals effectively. Furthermore, the reasonable correlation between the simulated waveforms and experimental acoustic emission signals obtained during quasi-static tensile test highlights the effectiveness of FEA in accurately modeling these failure modes in composite materials.

In order to determine if it is possible to predict the site and mode of failure under mechanical loading, different tree species were subjected to bending tests. Four species were examined: European beech, English oak, Douglas fir and Norway spruce. All trees were of a similar age and size. Strain gauges were placed on the surface of the trunk and along the lateral roots. Strain gauges measure deformations on the surface of a material during loading. Trees were winched horizontally using increments of force of 0.25 kN, and strain was measured in each of the strain gauges for each increment of force applied. Resistance of species to mechanical failure was in the order: beech, oak, Douglas fir and spruce. Beech required over three times as much force to cause stem breakage, compared to spruce which generally broke in the root system. Oak also broke in the trunk whilst Douglas fir usually broke at the root/stem joint. In those species which broke in the trunk, strain was always found to be higher in the stem than in the roots during winching. However, in Douglas fir and Norway spruce, strain was always highest at the root/stem joint and in the root system, respectively. Root system architecture may influence the mode of failure as beech, oak and Douglas fir all have deeper growing roots than spruce, and they all broke above ground level. However, a more detailed study of tree architecture and wood properties would be needed to verify this hypothesis. It appears that through the use of winching tests and strain measurement, it may be possible to predict how and where a tree might fail under mechanical loading. More species and trees of different ages and in different states of health would need to be examined using this method.

Feasibility study of the application of voltage contrast to printed circuit board