Example10 Multi-Step Thermal Load Analysis for IC Soldering Process

General

An IC is underfilled after mounted and soldered on a substrate.
The process involves several temperature changes. The mechanical stresses during the process are analyzed.
The reached temperature is set on each step. Bodies can be included in the analysis at a specific step.
Using the same model, mechanical stress analysis with solder’s elasto-plasticity and creep taken into account is explained in
Exercise 8: Mechanical Stress Analysis of Operating IC after Soldering
The distributions of the displacement and the mechanical stress are solved for each temperature.
Unless specified in the list below, the default conditions will be applied.

Analysis Space

Item	Settings
Analysis Space	2D
Model unit	mm

Analysis Conditions

To simplify the analysis, the 2-D model is analyzed.

Select the thermal load option.

Item	Settings
Solver	Mechanical Stress Analysis [Galileo]
Analysis Type	Static analysis
Options	Select “Thermal load”.

The process is as follows.

Step 1 The IC is soldered on the substrate at 220[deg] and cooled down to 25[deg].

Step 2 The temperature is increased from 25[deg] to 120[deg].

Step 3 At 120[deg], the underfill is applied and hardened. After the hardening, the temperature is decreased to 25[deg].

Step 4 The temperature is increased from 25[deg] to 85[deg].

The Step/Thermal Load tab is set as follows.

The temperature profile is set as follows.

Tabs

Setting Item

Settings

Step/Thermal Load

Step Setting

Multi-step thermal load analysis

Reference temperature

220[deg]

Step/Reached Temperature Setting

Step	Substeps	Reached temperature [deg]
1	1	25
2	1	120
3	1	25
4	1	85

The underfills are subjected to the analysis on and after Step 3. Therefore, the setting is done on the Analysis Domain tab of the Body Attribute.

Model

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Sheet	PCB	GLASS_EPOXY
1/Sheet	BGA	EPOXY
3/Sheet	SB	SOLDER
4/Sheet	SB	SOLDER
5/Sheet	SB	SOLDER
6/Sheet	SB	SOLDER
11/Sheet	UF	UNDER_FILL
12/Sheet	UF	UNDER_FILL
13/Sheet	UF	UNDER_FILL
14/Sheet	UF	UNDER_FILL
15/Sheet	UF	UNDER_FILL
16/Sheet	BGA	GLASS_EPOXY

The material properties are set up as follows:

Material Name

Tab

Properties

GLASS_EPOXY

Elasticity

Young’s modulus: 28×10^9[Pa]

Poisson’s ratio: 0.3

Coefficient of Expansion

Anisotropy: Select Anisotropic.

Vector of expansion coefficient

1	11×10^-6[1/deg]
2	11×10^-6[1/deg]
3	55×10^-6[1/deg]

EPOXY

Elasticity

Young’s modulus: 19×10^9[Pa]

Poisson’s ratio: 0.3

Coefficient of Expansion

11×10^-6[1/deg]

SOLDER

Elasticity

Young’s modulus: 31×10^9[Pa]

Poisson’s ratio: 0.4

Coefficient of Expansion

21×10^-6[1/deg]

UNDER_FILL

Elasticity

Young’s modulus: 3.5×10^9[Pa]

Poisson’s ratio: 0.3

Coefficient of Expansion

90×10^-6[1/deg]

UF is set up as follows.

Body Attribute Name

Tab

Settings

Analysis Domain

Birth/Death Setting:

Step 1: No
Step 2: No
Step 3: Yes
Step 4: Yes

Boundary Conditions

N/A

Results

The vectors of the mechanical stress at each step are shown below.

The minimum/maximum values of the vectors are set to 0 -> 200M on the vector tab of Graphics Setup.

Step 1: Reached temperature 25 [deg]:

Step 2: Reached temperature 120 [deg]:

Step 3: Reached temperature 25 [deg]:

Step 4: Reached temperature 85 [deg]:

The mechanical stresses increase when the ambient temperature changes further away from the hardening temperature. .

By comparing Step 1 and Step 3, you can see that the shrinkage of the underfill causes the stress on IC and the substrate.

See other Stress Analysis examples.