Underfill Design for Low-k Dielectrics and Lead Free Applications

2010 ◽  
Vol 2010 (DPC) ◽  
pp. 001465-001485
Author(s):  
Brian Schmaltz ◽  
Yukinari Abe ◽  
Kazuyuki Kohara
Keyword(s):  
Stress Concentration ◽  
Dielectric Layer ◽  
Failure Modes ◽  
High Stress ◽  
High Strength ◽  
Lead Free ◽  
Typical Result ◽  
High Stress Concentration ◽  
Technology Nodes ◽  
Low K

As technology nodes progress to 32/28nm and beyond underfill materials are presented with the significantly challenging task of maintaining bump protection while ensuring ultra low-K dielectric (ULK/ELK) integrity. This challenge is further complicated by the trend toward RoHS compliancy(lead-free) and a ever increasing die size. Through extensive research and testing, several specifically formulated underfill materials were determined acceptable solutions for these complex issues. As technology nodes progress to smaller process generations a high stress concentration is seen at the dielectric layer during thermal cycling. This stress is a typical result of a high glass transition temperature (Tg) / high strength material that often leads to a cracking failure mode of the thin dielectric layer. Too low of a Tg presents a high stress concentration on the bumps which once again constitutes failure, this time however the crack is typically seen at the bump location. This high stress concentration seen at the bumps is more significant when lead free bumps are considered due to their inherent fragile nature. Underfill materials must now be specifically formulated and optimized to solve these failure modes for a large variable of package types. This paper will discuss solutions to typical failure modes currently seen with reliability testing of present and future technologies.

Packaging Materials for Flip Chip and WLP: Underfill Design Using FEM for FC-BGA, FC-CSP, and Moving Towards 2.5/3D.

2014 ◽  
Vol 2014 (DPC) ◽  
pp. 001295-001327
Author(s):  
Brian Schmaltz ◽  
Yukinari Abe ◽  
Kazuyuki Kohara
Keyword(s):  
Stress Concentration ◽  
Dielectric Layer ◽  
Flip Chip ◽  
Failure Modes ◽  
High Stress ◽  
Lead Free ◽  
Typical Result ◽  
Stress Concentrations ◽  
High Stress Concentration ◽  
Technology Nodes

As technology nodes progress to 16/14nm and beyond underfill materials are presented with the significantly challenging task of maintaining bump protection while ensuring low warpage for ultra low-K dielectric (ULK/ELK) integrity. This challenge is further complicated by the trend toward RoHS compliancy (lead-free) and an ever increasing die size (beyond 25x25mm). Through extensive research and testing, several specifically formulated underfill materials were determined acceptable solutions for these complex issues. As technology nodes progress to smaller processes high stress concentrations are seen at the dielectric layer during thermal cycling. This stress is a typical result of a high glass transition temperature (Tg) / high strength material that often leads delamination or a cracking failure mode of the thin dielectric layer. Too low of a Tg presents a high stress concentration on the bumps which once again constitutes failure, this time, however, the crack is typically seen at the bump location. This high stress concentration seen at the bumps is more significant when lead free bumps are considered due to their inherent fragile nature. Underfill materials must now be specifically optimized for variable package conditions to solve these failure modes for a large variation of package designs. Desired material properties must be quickly calculated using finite element methods. This paper will discuss solutions to typical failure modes currently seen in reliability testing of present and future technologies.

An Experimental Study of Cavity Nucleation During Superplastic Deformation

1990 ◽  
Vol 196 ◽  
Author(s):  
Jiang Xinggang ◽  
Cui Jianzhong ◽  
Ma Longxiang
Keyword(s):  
Grain Boundary ◽  
Superplastic Deformation ◽  
Thermomechanical Processing ◽  
High Stress ◽  
High Strength ◽  
Optical Microscope ◽  
Grain Boundary Sliding ◽  
Cavity Nucleation ◽  
High Stress Concentration ◽  
Voltage Electron

ABSTRACTCavity nucleation during superplastic deformation of a high strength aluminium alloy has been studied using a high voltage electron microscope and an optical microscope. The results show that cavities nucleation is due only to superplastic deformation and not to pre-existing microvoids which may be introduced during thermomechanical processing. The main reason for cavity nucleation is the high stress concentration at discontinuties in the plane of the grain boundary due to grain boundary sliding.

Fracture Assessments of High Pressure Vessel Components Having Longitudinal Holes

2017 ◽  
Author(s):  
Yu Xu ◽  
Kuao-John Young
Keyword(s):  
High Pressure ◽  
Stress Concentration ◽  
Fracture Mechanics ◽  
Pressure Vessel ◽  
High Stress ◽  
Pressure Vessels ◽  
Crack Face ◽  
High Pressure Vessel ◽  
High Stress Concentration ◽  
Critical Locations

Small size longitudinal holes are common in components of high pressure vessels. In fracture mechanics evaluation, longitudinal holes have not drawn as much attention as cross-bores. However, longitudinal holes become critical at certain locations for such assessments because of high stress concentration and short distance to vessel component wall. The high stress concentration can be attributed to three parts: global hoop stress that is magnified by the existence of the hole, local stresses due to pressure in the hole, and crack face pressure. In high pressure vessel design, axisymmetric models are used extensively in stress analyses, and their results are subsequently employed to identify critical locations for fracture mechanics evaluation. However, axisymmetric models ignore longitudinal holes and therefore cannot be used to identify the critical location inside the holes. This paper is intended to highlight the importance of including longitudinal holes in fracture mechanics evaluation, and to present a quick and effective way of evaluating high stress concentration at a longitudinal hole using the combined analytical solutions and axisymmetric stress analysis results, identifying critical locations and conducting fracture mechanics evaluation.

Reduction of Stress Concentration Due to Interference Fits in an Infinite Plate With Two Holes

1978 ◽  
Vol 100 (4) ◽  
pp. 369-373
Author(s):  
T. Iwaki ◽  
K. Miyao
Keyword(s):  
Exact Solution ◽  
Stress Concentration ◽  
Elastic Properties ◽  
High Stress ◽  
Infinite Plate ◽  
Concentration Effects ◽  
Numerical Examples ◽  
High Stress Concentration ◽  
External Forces

This paper contains an exact solution for stresses which are produced in an infinite plate with two holes of different sizes by interference fits. It is assumed that the plate and the interference-fitted ring have the same elastic properties and are perfectly bonded to each other. Numerical examples of the solution are worked out and the interference fits are found useful for reducing the high-stress concentration effects which are induced in an infinite plate with two holes by external forces.

scholarly journals Study on the Mechanism and Control of Rock Burst of Coal Pillar under Complex Conditions

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Xingping Lai ◽  
Huicong Xu ◽  
Jingdao Fan ◽  
Zeyang Wang ◽  
Zhenguo Yan ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Rock Burst ◽  
Coal Mine ◽  
High Stress ◽  
Coal Pillar ◽  
Vertical Stress ◽  
Body Area ◽  
High Stress Concentration ◽  
Solid Coal ◽  
Working Face

In order to explore the mechanism of coal pillar rock burst in the overlying coal body area, taking W1123 working face of Kuangou Coal Mine as the engineering background, the full mining stage of W1123 is simulated by FLAC3D. It is found that the high stress concentration area has appeared on both sides of the coal pillar when W1123 does not start mining. With the advance of the working face, the high stress concentration area forms X-shaped overlap. There is an obvious difference in the stress state between the coal pillar under the solid coal and the coal pillar under the gob in W1123. The concrete manifestation is that the vertical stress of the coal pillar below the solid coal is greater than the vertical stress of the coal pillar below the gob. The position of the obvious increase of the stress of the coal pillar in the lower part of the solid coal is ahead of the advancing position of the working face, and the position of the obvious increase of the stress of the lower coal pillar in the gob lags behind the advancing position of the working face. At the same time, in order to accurately reflect the true stress environment of coal pillars, the author conducted a physical similarity simulation experiment in the laboratory to study the local mining process of the W1123 working face, and it is found that under the condition of extremely thick and hard roof, the roof will be formed in the gob, the mechanical model of roof hinged structurer is constructed and analyzed, and the results show that the horizontal thrust of roof structure increases with the increase of rotation angle. With the development of mining activities, the self-stable state of the high stress balance in the coal pillar is easily broken by the impact energy formed by the sudden collapse of the key strata. Therefore, the rock burst of coal pillar in the overlying coal body area is the result of both static load and dynamic load. In view of the actual situation of the Kuangou Coal Mine, the treatment measures of rock burst are put forward from the point of view of the coal body and rock mass.

Failure Studies on Flow Formed High Strength Pressure Vessel: A Case Study

2003 ◽  
Vol 125 (3) ◽  
pp. 253-259 ◽  
Author(s):  
K. M. Rajan ◽  
K. Narasimhan
Keyword(s):  
Tensile Strength ◽  
High Stress ◽  
High Strength ◽  
Thickness Reduction ◽  
Flow Forming ◽  
High Stress Concentration ◽  
Micro Cracks ◽  
Aisi 4130 ◽  
As Stress ◽  
Stress Raisers

High strength thin walled flow formed tubes are manufactured from AISI 4130 medium carbon low alloy steel. Starting with an ultimate tensile strength of 650 MPa, the material has recorded a tensile strength of 1250–1300 MPa corresponding to a percentage thickness reduction of 88. It has been observed that material with higher impurity levels and inclusion ratings are more vulnerable to development of micro cracks at higher percentage thickness reduction. Deformed inclusions like MnS act as stress raisers leading to initiation of micro cracks. Hard to deform inclusions like silicates create high stress concentration at inclusion-matrix interface, leading to de-cohesion and finally cracking. The presence of dissolved gas contents, particularly hydrogen, are harmful in flow forming. Hydrogen embrittlement is a serious problem which is likely to lead to cracking of the flow formed tube. It could be concluded from this study that clean steel (electro slag refined) processed through hardening and tempering route with a maximum percentage reduction in thickness of 88 or less can give consistently very high strength of the order of 1250–1300 MPa for AISI 4130 steel.

Development of Design Curve for Sweepolet Subjected to Acoustic Induced Vibration

2016 ◽  
Author(s):  
Yuqing Liu ◽  
Philip Diwakar ◽  
Dan Lin ◽  
Ismat Eljaouhari ◽  
Ajay Prakash
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Failure ◽  
High Stress ◽  
Peak Stress ◽  
Acoustic Energy ◽  
Piping System ◽  
Element Analysis ◽  
Design Curve ◽  
High Stress Concentration

High acoustic energy has the potential to cause severe Acoustic Induced Vibration (AIV) that leads to fatigue failure at high stress concentration regions such as fittings in a piping system. Sweepolet fittings have been extensively used as mitigation to counteract the risk of fatigue failure caused by AIV. The advantages of a sweepolet are its integrally reinforced contoured body and low stress concentration. However, there are inconsistencies in published standards and regarding the design limits for sweepolet subjected to AIV. In this paper, Finite Element Analysis is conducted to simulate high frequency pipe shell wall vibration caused by acoustic energy inside the pipe. Peak stress and the associated minimum fatigue life are calculated for sweepolet and sockolet under the same acoustic excitation. By comparing the stress level to that of a sockolet whose design limit to AIV had been published, the design curve and fatigue life equation for sweepolet are developed.

Providing Cyclic Robustness of Bolted Joints in Case of Assembly with Implementation of Anaerobic Materials

2019 ◽  
Vol 952 ◽  
pp. 3-12
Author(s):  
Igor Ivanovich Voyachek ◽  
Milan Sága ◽  
Zuzana Ságová ◽  
Denis Viktorovich Kochetkov ◽  
Vladimir Zinovievich Zverovschikov ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Load Distribution ◽  
Crack Formation ◽  
Rupture Strength ◽  
High Stress ◽  
Bolted Joints ◽  
High Stress Concentration ◽  
Materials Modelling ◽  
Nonuniform Load ◽  
Elastic Layers

Stress concentration in thread roots and nonuniform load distribution along thread turn are the major disadvantages of bolted joints. Under changing cyclic loads on areas of high stress concentration crack formation and destruction of parts occur. In addition, the fretting corrosion processes activate in the areas of contact between thread turns. The purpose of the work is to increase rupture strength of bolted joints under the action of cyclic forces by decreasing stress concentration and reducing movements in contact zone of mating parts in case of assembly with implementation of anaerobic materials. Modelling of bearing strength of bolted joints is conducted according to finite element method, with theory of contact interaction between mating surfaces being used. The results of experimental research are given. Anaerobic materials which polymerize in area of thread contact of parts are used. It was established that assembly with implementation of anaerobic material allows unloading of thread turns because the part of external load is received by elastic layers of the polymerized anaerobic material. In this case the level and the concentration of stress in thread roots reduce, relative movements are decreased, the joint becomes more rigid and its cyclic robustness grows.

Simulation Research on Stress of Polymeric Patterns during Micro Hot Embossing

2011 ◽  
Vol 80-81 ◽  
pp. 339-345 ◽  
Author(s):  
Ting Zhang ◽  
Yong He ◽  
Jian Zhong Fu
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
High Stress ◽  
Hot Embossing ◽  
Duty Ratio ◽  
Simulation Research ◽  
High Stress Concentration ◽  
Simulation Results

The properties of polymeric components made by hot embossing are obviously affected by the geometry of the mold such as the duty ratio, the aspect ratio, width to thickness ratio and the mold cavity position. This paper focuses on numerical simulations with isothermal embossing conditions in order to observe the stress distribution and the stress concentration of the polymeric patterns. The simulation results show that stress concentration in the PMMA resist accumulates at the contact corner between the mold and the polymer, and the location of the stress distribution is mainly on the profile of the replicated patterns. Small duty ratio will result in high stress concentration at the corner of the replicated components. The stress concentration also increases rapidly while the aspect ratio of the mold increases. The thicker the polymer is, the more difficult the adequate flow of the polymer becomes, and the stress concentration rises up. A stress barrier can be used in the mold in order to reduce the stress concentration in the middle of the replicated polymeric patterns.

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