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Fall 2015 Probe Testing ANSYS Study

For ON SEMICONDUCTORBy: Justin Smith

BackgroundON SEMICONDUCTOR has completed previous Finite Element Analysis (FEA) studies to make a comparison with a Probe testing tip and the Bonding Pads of a wafer board. A wafer board is an 8” disk with layers of Silicon, SiO2, and Aluminum, which creates a circuit board chip used in cell phones and other technologies. During physical testing, the SiO2 layers between the aluminum at times will crack, causing a short circuited malfunctioning part. After Static FEA analysis was completed, it was suggested that a Dynamic analysis should be made to further better understand the causing of the cracking layers.

Photo credit: Wikipedia.com

Figure 1: 8” Wafer Board Probe Tester

DiscussionThe results of a Dynamic Study, once completed would allow for more accurate results. This study serves as a “standard work process” (step by step instruction manual) to allow for future studies done with different Probe Models with different shapes and angles to suggest as which probe should be implemented in future physical probe testing.

0.8um-0.9Tip-13-LowTo begin the study it is necessary to first select an IGES (.igs) file as described in the next slide. We will proceed with 0.8um-0.9Tip-13-Low.

Import Selected IGES.igs from the Google Drive• Start up ANSYS Workbench 16.2 • Create a new “Static Structural” Study and save project workbook as the

IGES File name. • Right click Geometry\Import Geometry\Browse . . .

• Locate IGES File: My Drive\BYU-I ANSYS\Probe IGES Models

• Ex: 0.8um-0.9Tip-13-Low.igs

Import IGES.igs• Add a Transient Structural Study as a Dynamic Study.

• The material data for each material was referenced from the data sheet located on the Google Drive [Material Properties.xlsx].• Aluminum• Silicon• SiO2• Tungsten

• Make sure to double check the material properties under the “Engineering Data” section before running your program, once you load the Project Workbook on a new computer, the default units may be chosen, if so, you may have to change the units as shown in the next slide. • Don’t forget to check the units as you open the “Geometry” or “Model” sections.• Units should be in Metric.

Engineering Data: Material properties

GeometrySection View

Probe Tip on Aluminum Bonding Pad

Full length Probe with bonding pad

• Only include “Solid” objects, suppress “Surface Bodies”

Geometry:

Model:Material Selection:• Al-out : SiO2• Solid Out2: SiO2• Solid Out3: SiO2• Solid Out4: SiO2• Solid Out5: SiO2• Solid Out6: SiO2• Solid Out7: SiO2• Solid Out8: SiO2• Solid Out9: Silicon• Probe – Body: Tungsten

Material Selection:• Al: Aluminum• Solid In2: SiO2• Solid In3: Aluminum• Solid In4: SiO2• Solid In5: Aluminum• Solid In6: SiO2• Solid In7: Aluminum• Solid In8: SiO2• Solid In9: Silicon• Probe – Tip: Tungsten

Model: Connections (Contacts)• Contact Type used

between probe tip and aluminum pad: Frictional.

• The ‘X’ distinguishes a suppressed contact that is unrelated of the 105 contacts automatically generated from an IGES File.

• Once a contact is accepted, it automatically receives a new name: • Ex: “Contact Region

2” -> “Frictional – Al To Probe – Tip”

Model: Connections (Contacts)Inside 4 Faces

Outside 4 Faces

Model: Connections (Contacts)

As shown in the previous slide, the right hand side shows two windows with a red and blue shape. The red depicts the face of the ‘Contact Body’(top layered body with contacting face at the bottom of that part) while the ‘Target Body’ (is the lower leveled part with the upper face as the contact face) is shown in blue.

It is standard for .igs files to select both top and bottom faces for each part. Since one face of the contact body is in contact with one face of the target body,

Model: Connections

Model: Connections (Contacts)

Model: Mesh

• Due to the limited amount of nodes and elements, the element size has been reduced.• If you are able to have enough nodes

and elements, you will have a much better success rate.

Nodes: 15,798Elements: 6,648

Model: Mesh (Body Sizing Al)

Model: Mesh (Hex Dominant Method Probe Body)

• This Meshing Method has not been utilized due to a restraint on the number of nodes and element sizes. It was however used in previous FEA simulation models.

Model: Mesh (Hex Dominant Method Probe Tip)

• In comparison to the previous slide, this method was utilized because the part is relatively small and able to be calculated.

Model: Mesh (Body Sizing Outer)• This shows the Method for body sizing of the outer pieces. *Note: the

Element Size is a lot smaller than previous ANSYS studies done January through August 2015, where most body sizing are X.XXXe-6, because of the restriction of Element and Nodes, this remains true for all of the Body Sizing Meshes.

Model: Mesh (Body Sizing Probe Body)• This was adapted to create a mesh on the Probe Body due to the

restriction of Nodes and Elements made in this study. *This Mesh Method replaces the Hex Dominant Method for the Probe Body.

Model: Mesh (Face Meshing)• This is an additional Mesh Study, to see if there would be any drastic

changes in the model.

Static Structural: Analysis Settings

Static Structural: Fixed Support

38 Faces: All Pad Exterior Faces(4 Sides X 9 Pad Layers)=36Inside and Outside Bottom faces =2

Static Structural: Displacement

1 Face: As shown in Yellow.The Displacement should be directed in the –Y Direction as shown in the coordinates

Static Structural: Solution (Maximum Principal Stress)

*SiO2 Ultimate Tensile Strength is 76 MPa

*Exceeds tensile strength for SiO2 (2.81E8 Pa is larger than 76E6 Pa)

*This wafer board will crack during probe testing

*Top 3 Layers*

Static Structural: Solution (Maximum Principal Stress 2)




*Top 3 Layers with Probe*

Static Structural: Solution (Directional Deformation)

*The Max Deformation is going to be pushed in the negative Y-Direction and will have a value of 1.22E-7 m.


Static Structural: Solution (Directional Deformation 2)


*Top 3 Layers*

Static Structural: Solution (Equivalent Stress)




*Top Layer*

Static Structural: Solution (Equivalent Stress 2)




*Top 3 Layers*





*Top Layer*





*2nd Layer*

Transient Structural: Analysis Settings

Transient Structural: Fixed Support

38 Faces: All Pad Exterior Faces(4 Sides X 9 Pad Layers)=36Inside and Outside Bottom faces =2

Transient Structural: Displacement

1 Face: As shown in Yellow.The Displacement should be directed in the –Y Direction as shown in the coordinates

Transient Structural: Solution (Maximum Principal Stress)




*Top 3 Layers*

Transient Structural: Solution (Maximum Principal Stress 2)





Transient Structural: Solution (Directional Deformation)



Transient Structural: Solution (Total Deformation)

*Total: ALL Parts*

Transient Structural: Solution (Directional Deformation 2)


*Top 3 Layers*

Transient Structural: Solution (Equivalent Stress)




*Top Layer*

Transient Structural: Solution (Equivalent Stress 2)




*Top 3 Layers*





*Top Layer*





*2nd Layer*

Results and Conclusion• Through the duration of the Semester, I have made progress on the Dynamic FEA Study using

ANSYS Workbench 16.2 software. A greater understanding of Finite Element Methodology was gained through many hours of real life application of a real life problem. Some areas of concentration include:• Static V.S. Dynamic Simulations, loading .igs files, Engineering Data, Geometry, Contact Connections,

Mesh Methods, Emphasis of the number of nodes and elements, along with solving and comparing results to Tensile Stresses of a material found in Engineering Data.

• Once a deeper interest if the study was centered on the Contacts Connections of the Model, a successful Analysis was made. The most noticeable contribution was that during the Dynamic Modeling, the Probe Tip did not puncture or poke through the bonding pad.

• The results from this study show a great step forward in the Dynamic Modeling of the Probe Tip Analysis.

• Through this power point presentation, a person would be able to follow the steps in creating other Dynamic Model Simulations using the 60+ IGES files provided by ON SEMICONDUCTOR.

Suggestions for Improvement• Where possible, work at the same computer workstation and save your work to that

hard drive. I’ve found that when I save work on an academic computer where the capability has a limit of 250,000 Nodes and Elements and copy or save my work to a flash drive or the Google Drive, and work on a personal laptop computer with the student version which has a limit of 32,000 Nodes and Elements, it sometimes cannot open or read the .wbpj files.

• Refer to previous documentation located on the Google Drive:• Increase amount of Elements and/or reduce the Element Sizing for more concise results.• Replicate the settings for the Max Principle Stress etc. found under the Solution Tab of the Model. • If applicable, divide the probe into different sections or parts (as depicted in the “Excel Worksheet

for Probe Models.xlsx” under slide 2 “Base Model Map”) and unite them together as one Part in the Geometry Developer, switch to the Modeling Developer and make sure that the contact points are bonded. Then create a mesh type with smaller body sizing for each part to be uniform with each other, the smaller the better.

• Refer to “ANSYS Simulation Results-Short.pptx” as a guide for accumulating results when carrying out a simulation study and while gathering information for writing a report.

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