The Mechanism of the Low-K Stress Reduction in Chip Assembly by Shorter Solder Bump Height

2017 ◽  
Author(s):  
Keiji Matsumoto ◽  
Keishi Okamoto ◽  
Hiroyuki Mori
Keyword(s):  
Stress Relaxation ◽  
Stress Reduction ◽  
Solder Bump ◽  
Bending Moment ◽  
Bump Height ◽  
Joint Width ◽  
Low K ◽  
Joint Material

To solve the low-k delamination in chip assembly for high-end servers, our hypothesis is proposed that the low-k stress is determined by the bending moment and the stress relaxation of a joint. In our hypothesis, the low-k stress decreases as the joint height (SnAg bump height) becomes shorter, such as below 80μm, in 150μm-pitch joints. Our hypothesis is supported by simulation, in which the low-k stress is investigated as a function of the joint height, the joint material and also the joint width (the joint pitch). Finally, experiments are performed to evaluate the low-k delamination as a function of the joint height and our hypothesis is also supported by experiments.

Performance of self-centering steel moment frame considering stress relaxation in prestressed cables

2020 ◽  
Vol 23 (9) ◽  
pp. 1813-1822
Author(s):  
Seyyed Morteza Asadolahi ◽  
Nader Fanaie
Keyword(s):  
Stress Relaxation ◽  
Stress Reduction ◽  
Original Position ◽  
Dissipated Energy ◽  
Moment Frame ◽  
Steel Moment Frame ◽  
Moment Resisting Frames ◽  
Moment Resisting Frame ◽  
Moment Resisting ◽  
Over Time

Buildings can be designed to limit the earthquake-induced damage to members that can easily be repaired. Self-centering moment-resisting frames can be used as effective structural systems for this purpose. Self-centering moment-resisting frames with prestressed cables are able to return the structure to its original position after the earthquake. The internal forces in self-centering moment-resisting frames are transferred between the beam and the column by post-tensioned cables. As a main member of self-centering connections, prestressed cables play a significant role in such systems. Cable tension decreases over time due to the effect of stress relaxation on the performance of the system. Stress relaxation is a time-dependent phenomenon causing stress reduction over time in the members prestressed at a constant strain. Therefore, the effect of stress relaxation on the performance of self-centering moment-resisting frames can be significant. In this article, after simulating and validating a moment-resisting frame with self-centering connections, stiffness and moment–rotation hysteresis diagrams were analyzed after 0, 1, 5, 10, and 20 years of cable prestressing. According to the results, two equations were presented to estimate the reduction in the connection stiffness and dissipated energy by the system based on prestressing level and the time after prestressing. The proposed equations could be used to model semi-rigid connections.

Underfill Assessments and Validations for Low-k FCBGA

2006 ◽  
Author(s):  
Nicholas Kao ◽  
Jeng Yuan Lai ◽  
Jase Jiang ◽  
Yu Po Wang ◽  
C. S. Hsiao
Keyword(s):  
Finite Element ◽  
High Speed ◽  
Flip Chip ◽  
Failure Modes ◽  
Solder Bump ◽  
Material Selection ◽  
Coefficient Of Thermal Expansion ◽  
Electrical Performance ◽  
Low K ◽  
Underfill Material

With the trend of electronic consumer product toward more functionality, high performance and miniaturization, IC chip is required to deliver more I/Os signals and better electrical characteristics under same package form factor. Thus, Flip Chip BGA (FCBGA) package was developed to meet those requirements offering better electrical performance, more I/O pins accommodation and high transmission speed. For high-speed application, the low dielectric constant (low-k) material that can effectively reduce the signal delays is extensively used in IC chips. However, the low-k material possesses fragile mechanical property and high coefficient of thermal expansion (CTE) compared with silicon chip, which raises the reliability concerns of low-k material integrated into IC chip. The typical reliability failure modes are low-k layer delamination and bump crack under temperature loading during assembly and reliability test. Delamination is occurred in the interface between low-k dielectric layers and underfill material at chip corner. Bump crack is at Under Bump Metallization (UBM) corner. Thus, the adequate underfill material selection becomes very important for both solder bump and low-k chips [1]. This paper mainly characterized FCBGA underfill materials to guide the adequate candidates to prevent failures on low-k chip and solder bump. Firstly, test vehicle was a FCBGA package with heat spreader and was investigated the thermal stress by finite element models. In order to analyze localized low-k structures, sub-modeling technique is used for underfill characterizations. Then, the proper underfill candidates picked from modeling results were experimentally validated by reliability tests. Finally, various low-k FCBGA package structures were also studied with same finite element technique.

Plastic Coupling and Stress Relaxation During Nonproportional Axial-Shear Strain-Controlled Loading

2000 ◽  
Vol 123 (1) ◽  
pp. 81-87
Author(s):  
Cliff J. Lissenden ◽  
Steven M. Arnold ◽  
Atef F. Saleeb
Keyword(s):  
Stress Relaxation ◽  
Shear Strain ◽  
Stress Reduction ◽  
Large Range ◽  
Axial Stress ◽  
Axial Strain ◽  
Time Dependent ◽  
Load Path ◽  
Percent Reduction ◽  
Material Parameters

A nonproportional strain-controlled load path consisting of two segments was applied to the cobalt-based alloy Haynes 188 at 650°C. The first segment was purely axial; the axial strain was then held constant while the shear strain was increased during the second segment. The alloy exhibited about a 95-percent reduction in axial stress (298 to 15 MPa) during shear straining. This reduction was due primarily to plastic coupling, but time-dependent stress relaxation also occurred. A rate-independent plasticity model approximated the stress reduction due to plastic coupling reasonably well, but as expected was unable to account for time-dependent stress relaxation. A viscoplasticity model capable of predicting the interaction between stress relaxation and plastic coupling also predicted the plastic coupling reasonably well. The accuracy of the viscoplastic model is shown to depend greatly upon the set of nonunique material parameters, which must be characterized from a sufficiently large range of load histories.

Experimental Testing and Finite Element Modeling of Bump Wafer Probing

2013 ◽  
Vol 284-287 ◽  
pp. 748-753
Author(s):  
Hao Yuan Chang ◽  
Kao Hua Chang ◽  
Yi Shao Lai
Keyword(s):  
Finite Element ◽  
Solder Bump ◽  
Experimental Testing ◽  
Three Dimensional ◽  
Element Model ◽  
Simulation Software ◽  
Experimental Results ◽  
Height Variation ◽  
Bump Height ◽  
Wafer Probing

The purpose of this paper is mainly to develop a method to simulate the bump height variation and probe mark profile for Eutectic (Sn63/ Pb37) bump wafer probing with continuing-touchdown probing. Certainly, the bump height variation and probe mark area on the solder bump influence the quality of the wafer probing and further impacts reliability of the packaging process after wafer probing to cause issues of cold-joint and needle damage. A three-dimensional computational model of was developed to analyze the contact phenomena between the vertical needle and the solder bump. Finite element simulation software, ANSYS, is used to analyze the loading force distributed on the vertical needle with various overdrives. In addition, the results of the bump height variation and probe mark area, which predicted by the finite element method (FEM), were verified against the on-line experimental results. Finally, the results predicted by the finite element model is consistent with experimental results and the numerical method presented in the paper can be used as a useful evaluating method to support the choice of suitable probe geometry and wafer probe testing parameters.

Solder Bump Strength and Failure Mode of Low-k Flip Chip Device

2006 ◽  
Author(s):  
Zulkarnain Endut ◽  
Ibrahim Ahmad ◽  
Gary Lee How Swee ◽  
Norazham Mohd Sukemi
Keyword(s):  
Failure Mode ◽  
Flip Chip ◽  
Solder Bump ◽  
Low K

Solder Bump Electromigration and CPI Challenges in Low-k Devices

2019 ◽  
Vol 16 (19) ◽  
pp. 51-60 ◽  
Author(s):  
Robin Susko ◽  
Timothy Daubenspeck ◽  
Thomas Wassick ◽  
Timothy Sullivan ◽  
Wolfgang Sauter ◽  
...  
Keyword(s):  
Solder Bump ◽  
Low K

Research on Reheat Cracking Criterion of CGHAZ in 2.25Cr1Mo0.25V Steel

2018 ◽  
Author(s):  
Chang-Jun Liu ◽  
Shuang Zhou ◽  
Jian-Ping Tan ◽  
Hao-Yu Zhang
Keyword(s):  
Stress Relaxation ◽  
Stress Reduction ◽  
Critical Strain ◽  
Coarse Grained ◽  
Reheat Cracking ◽  
Creep Coefficient ◽  
The Difference ◽  
Multiaxial Creep ◽  
Critical Strains ◽  
The Relationship

During the final post welding heat treatment (PWHT), residual stress relieves gradually with the accumulation of creep strain. However, reheat cracking with intergranular characteristic will occur when grain boundary cannot accommodate this kind of strain for some special steel welding, such as the welding coarse grained heat affected zone (CGHAZ) of 2.25Cr1Mo0.25V steel. Based on the principle of stress relaxation similar to the process of PWHT, two methods are applied to study the strain criterion of reheat cracking. Stress relaxation testing is performed on CGHAZ materials prepared by Gleeble thermomechanical simulator. The critical strain is calculated using the relationship between stress reduction and creep deformation. Self-loaded notched C-ring specimens are tested taken from the welding structure, coupled with finite element modeling and multiaxial creep coefficient to determine the critical strain. The results show that there is a large numerical difference between the critical strains from two methods. The possible reasons for the difference are given. Regarding the PWHT as a service process, whether the critical strain values obtained exceed the strain limits in ASME-NH is discussed.

Compressive stress relaxation through buckling of a low-k polymer-thin cap layer system

2003 ◽  
Vol 82 (9) ◽  
pp. 1380-1382 ◽  
Author(s):  
F. Iacopi ◽  
S. H. Brongersma ◽  
K. Maex
Keyword(s):  
Stress Relaxation ◽  
Compressive Stress ◽  
Layer System ◽  
Cap Layer ◽  
Low K
Sign in / Sign up

Export Citation Format

Share Document