scholarly journals Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 6817
Author(s):  
Nor Akmal Fadil ◽  
Siti Zahira Yusof ◽  
Tuty Asma Abu Bakar ◽  
Habibah Ghazali ◽  
Muhamad Azizi Mat Yajid ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Surface Finish ◽  
High Stress ◽  
Copper Substrate ◽  
External Stress ◽  
Tin Whiskers ◽  
Image Analyzer ◽  
Tin Coating ◽  
High Stress Concentration ◽  
Humidity Chamber

Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formation, which tends to endanger the efficiency of electronic circuits, and even worse, may cause short circuits to the electronic components. This research aims to investigate the effects of stress on tin whiskers’ formation and growth and the mitigation method for the immersion of the tin surface’s finish deposited on a copper substrate. The coated surface was subjected to external stress by micro-hardness indenters with a 2N load in order to simulate external stress applied to the coating layer, prior to storage in the humidity chamber with environmental conditions of 30 °C/60% RH up to 52 weeks. A nickel underlayer was deposited between the tin surface finish and copper substrate to mitigate the formation and growth of tin whiskers. FESEM was used to observe the whiskers and EDX was used for measuring the chemical composition of the surface finish, tin whiskers, and oxides formed after a certain period of storage. An image analyzer was used to measure the whiskers’ length using the JEDEC Standard (JESD22-A121A). The results showed that the tin whiskers increased directly proportional to the storage time, and they formed and grew longer on the thicker tin coating (2.3 μm) than the thin coating (1.5 μm). This is due to greater internal stress being generated by the thicker intermetallic compounds identified as the Cu5Sn6 phase, formed on a thicker tin coating. In addition, the formation and growth of CuO flowers on the 1.5 μm-thick tin coating suppressed the growth of tin whiskers. However, the addition of external stress by an indentation on the tin coating surface showed that the tin whiskers’ growth discontinued after week 4 in the indented area. Instead, the whiskers that formed were greater and longer at a distance farther from the indented area due to Sn atom migration from a high stress concentration to a lower stress concentration. Nonetheless, the length of the whisker for the indented surface was shorter than the non-indented surface because the whiskers’ growth was suppressed by the formation of CuO flowers. On the other hand, a nickel underlayer successfully mitigated the formation of tin whiskers upon the immersion of a tin surface finish.

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.

Effect of the Formation of CuO Flowers and SnO2 on the Growth of Tin Whiskers on Immersion Tin Surface Finish

2014 ◽  
Vol 695 ◽  
pp. 301-305 ◽  
Author(s):  
Nor Akmal Fadil ◽  
Siti Zahira Yusof ◽  
Ali Ourdjini ◽  
Tuty Asma Abu Bakar
Keyword(s):  
Surface Finish ◽  
External Stress ◽  
Tin Whiskers ◽  
Environmental Condition ◽  
Tin Whisker ◽  
Plating Method ◽  
Cu Substrates ◽  
Coated Surface ◽  
Immersion Tin ◽  
Immersion Plating

The effect of the formation of CuO flowers and SnO2on tin whiskers formation and growth in 30°C/60%RH environmental condition for tin surface finish had been studied. Immersion plating method was used to coat a layer of tin onto a copper, Cu substrates. The coated surface was subjected to external stress by micro hardness indenter with 2N load in order to simulate an external stress in coating layer and to promote the formation of tin whiskers. FESEM and EDX was used to study the type and chemical composition of whiskers and oxides formed. Image analyser was used to measure the whiskers length using JEDEC Standard No 22-A121A. After 1 week of the exposure under 30°C/60%RH environmental condition, kinked-type whiskers were formed and the whiskers growth were discontinued at week 4 due to the distruction at the end-tip of kinked-type tin whisker to grow further when it touched the coating surface. An obervation until 52 weeks of exposure time found that the formation and growth of CuO flowers and the oxidation of non-kinked-type of tin whiskers to form SnO2promoted by external stress also contributed to the discontinuity of whiskers growth.

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.

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.

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.

Fracture of Amorphous Polymeric Solids: Time to Break

1965 ◽  
Vol 38 (2) ◽  
pp. 263-277
Author(s):  
J. C. Halpin
Keyword(s):  
Tensile Strength ◽  
Stress Concentration ◽  
Nonlinear Response ◽  
Failure Process ◽  
High Stress ◽  
Viscoelastic Body ◽  
Simple Process ◽  
High Stress Concentration ◽  
Failure Theory ◽  
Fracture Theory

Abstract The failure theory of Bueche and Halpin is generalized and expanded to obtain a prediction of the time dependence of tensile strength and ultimate elongation. The model pictures rupture as propagation of tears or cracks within the material. The growth of a tear or crack is viewed as an ideally simple process in which the molecular chains at the tear tip stretch viscoelastically under the influence of a high stress concentration until they rupture. As a consequence, the failure process is a nonequilibrium one, developing with time and involving the consecutive rupture of the molecular chains. Substantial support for the theory is found by comparing the theoretical prediction with experimental results obtained for SBR and EPT. In addition, it is experimentally demonstrated that delayed and forced rupture experiments can yield qualitatively identical data for viscoelastic bodies. Also discussed is the basis for the approach to the nonlinear response of a viscoelastic body required here in the development of a fracture theory.

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