Manufacturing Process Mechanics

Individual Project (P2R2)

NAME: SIDDHESH OZARKAR

FR8695@WAYNE.EDU

DESIGNATION OF MODEL: P2R2

Model Number 2 with Radius of 0.015mm and 2nd

order elements (CPE8) used

Abstract: The main objective of the paper is to compare the fatigue life of solder balls in

completely filled & incompletely filled flip-chip packages & to understand the effect of

the Under-fill. The fatigue life of both the models is calculated by using Coffin-Manson

equation. The results from the analysis show that,

A fully filled model has much higher fatigue cycle sustaining capacity.

The Incompletely filled model shows possibility of earlier failure.

Flip-Chip Package

The term ‘Flip-chip’ is defined as an electronic component or semiconductor device that can be mounted directly on a substrate, board, or carrier in a face-down manner.

Components In a flip-Chip Package

Flip-Chip Package

Chip Substrate Solder

Balls Underfill

Dimensions and Geometry of Model

Completely Filled Model

Solid Works Model

Chip

Substrate

Solder Balls

Underfill

Incompletely Filled

Model

Solid Works Model

Chip

Under-fill Solder-Balls

Substrate

Radius Given as per

requirement.

Pre-Processing

1) The geometry of both the models completely filled and Incompletely Filled flip-chip

packages is created as per the given dimensions in Solidworks.

2) Only surface geometry were created in Solidworks, the files were exported (.IGES) to Hypermesh

3) Meshing was performed on these models in Hypermesh.

4) Surfaces representing the various components were Independently Meshed so as to achieve finer mesh where required.

5) Finer mesh was created where potential high stress concentration was suspected like the solder balls.

6) Edges were set to equivalence after meshing.

7) Properties of the mesh

Element type – CPE8

Smallest element size- 0.01mm

8) A solver deck containing the material properties for the various components of the package was imported in the Hypermesh file directory.

This solver deck was assigned to the model so that respective elements have respective properties.

9) Boundary conditions were applied as follows - Constraint the left vertical side with DOF-1, bottom horizontal side with DOF-2, and intersection of both with DOF-1,2 .

10) All nodes were defined in one Entity set for the ease of utility. This entity set also contains the initial temperature condition of the model.

11) Create 4 load collectors were created as follows- Constraint

Initial Temp(20C)

Temperature 233 K (–40°C)

Temperature 398 K (125°C)

12) Create Output block and 3 Load step. Step 1- Initial increment= 10 over a time period of 600 sec at temperature of 233 K Step 2- Increment= 10 over a time period of 900 sec at temperature of 398 K Step 3- Increment= 10 over a time period of 600 sec at temperature of 233 K

13) The file was then exported to Abaqus for Further Analysis.

Completely Filled Model

Fine meshing in Critical

Areas.

Coarse Mesh

Fine Mesh

Coarse Mesh

Fine Mesh

Fine Mesh

Fine Mesh helps capturing

the curves and fillet radius

more precisely.

Incompletely Filled Model

Analysis

1) The input file generated from Hypermesh (.inp) was fed to the Abaqus solver.

2) The Abaqus solver after performing a fatigue analysis on the file gives the following results.

3) The output request consists of

Stress (S)

Strain (PE)

Displacement (U)

Nodal Temperature (NT)

Completely Filled Model Incompletely Filled Model

Fully Filled Model:

Calculation of fatigue life

Step 1:

Max Strain = 1.318e-02

Min Strain = 6.063e-03

Step 2:

Max Strain = 5.938e-02

Min Strain = 7.298e-03

Step 3:

Max Strain = 1.912e-01

Min Strain = 9.377e-03

Step 1:

Max Strain = 1.099e-02

Min Strain = 8.443e-03

Step 2:

Max Strain = 1.306e-02

Min Strain = 8.99e-03

Step 3:

Max Strain = 1.355e-02

Min Strain = 9.063e-03

Fatigue Life of Solder Balls:

According to the Coffin-Manson’s equation,

(Nf)β ΔγP = CP

Where, β = Fatigue ductility exponent (β= 0.51) Nf = Fatigue life ΔγP = Applied plastic/inelastic strain range CP = Fatigue ductility coefficient. (CP= 1.14)

Considering the rightmost solder ball for analysis:

Model Step Number Max. Strain Min. Strain

Fully Filled 1 1.318e-02

6.063e-03

- 2 5.938e-02

7.298e-03

- 3 1.912e-01

9.377e-03

Incompletely Filled 1 1.099e-02 8.443e-03

- 2 1.306e-02

8.991e-03

- 3 1.355e-02 9.063e-03

Solder Ball Fully Filled Step 1 Solder Ball Fully Filled Step 2

A A B

A

B

A

D

C

D

C

C

MODEL A B C D

Fully FILLED 42850 55206 73410 34361

Incompletely FILLED 33525 67705.67 67710 20005.11

Solder Ball Incompletely Filled Step 1 Solder Ball Incompletely Filled Step 2

A A B

A

B

A

C D

C

D

C

C

Displacement for Fully Filled Model

Displacement for Incompletely Filled

Model

CONCLUSION:

Fatigue life of completely filled model is higher than that of the

incompletely filled model.

As compared to models with no radius present at the corners of the

solder balls the ones with a radius present show higher fatigue

sustaining capacity.

Due to the presence of radius the strain is more distributed and thus

results in extended life of flip chip package.