# Solder Fatigue Analysis

Solder fatigue is available to analyze and predict fatigue damage of the solder joint between a component and the base Printed Circuit Board (PCB).

Soldier joint failure between components and the PCB due to thermal loading is a major cause of breakdown in electronic products. It is critical to estimate such fatigue failure due to cyclic loading of solder joints. You can predict life of solder joints under thermal cyclic loads with solder fatigue.

Solder fatigue calculation due to mismatch of local thermal expansion coefficients (CTE) is available using the following solder joint types:
2. Ball Grid Array (BGA) solder joint

Fatigue damage due to local thermal expansion coefficient mismatch is assessed. The thermal expansion coefficient field (A) on the MAT1 Bulk Data Entry is mandatory.

The Strain range of the solder joint is calculated as:(1) $\text{Δ}\gamma =C\frac{{L}_{D}}{{h}_{s}}\text{Δ}\alpha \text{Δ}T$
Where,
${L}_{D}$
Component length (PKGLEN field on the FATSDR entry).
$\alpha$
Coefficient of thermal expansion (CTE) (A field on the MAT1 entry).
${h}_{s}$
Solder joint height. (PKGTHK field on the FATSDR entry).
$\text{Δ}\alpha =CT{E}_{p}-CT{E}_{c}$
Difference between thermal expansion coefficients of the PCB and the component soldered onto the board.
$T$
Input temperature.
$\text{Δ}T={T}_{p}-{T}_{c}$
Difference between temperatures of the PCB and the component soldered onto the board.
$C$
Empirical model constant for solder fatigue (specified using the C4GAMMA field on the PFATSDR entry). It is equal to $\frac{1}{\sqrt{2}}$ for leadless joint type. For BGA type, you can define the empirical model constant.
The strain energy dissipation per thermal cycle is calculated as:(2) $\text{Δ}W=0.5\cdot \text{Δ}\gamma \cdot \frac{F}{{A}_{s}}$
Where,
$F$
Shear force.
${A}_{s}$
Cross-section area.
The fatigue life is calculated as:(3) ${N}_{f}=\left(\frac{1}{{W}_{p}\cdot \Delta W}\right)$

Where, ${W}_{p}$ is the creep energy density for failure (Wp field of the MATFAT entry). The default value is 0.0019.

## Input/Output

Supported solder joint and output types for fatigue analysis.

The Leadless solder joint is activated by setting the SDRTYP field to XLEAD on the FATSDR entry. The joint is modeled with solid elements. Similarly, the Component/Package and the PCB are idealized with solid elements.

The Element SET ID which defines the Component Package should be defined with the SIDPKG field on the FATSDR entry.

The Element SET ID which defines the PCB should be defined on the SIDPCB field on the FATSDR entry.

Only two SDRis should be specified on the SOLDER continuation line of the FATSDR entry.

Only two Solder joints per package/component are allowed. Multiple FATSDR entries are allowed on a single FATDEF entry.

The FATEVNT entry should only contain a single FATLOAD reference.

The input temperature should be the same between the Package and the PCB.

If DIM continuation line on FATSDR is not defined, OptiStruct will attempt to measure it based on the Finite Element mesh.

### Ball Grid Array (BGA) Solder Joint

The BGA solder joint is activated by setting the SDRTYP field to BGA on the FATSDR entry. The joint is modeled with solid elements.

The Element SET ID which defines the Component Package should be defined with the SIDPKG field on the FATSDR entry.

The Element SET ID which defines the PCB should be defined with the SIDPCB field on the FATSDR entry.

A single SDRi is allowed on the SOLDER continuation line of the FATSDR entry.

Multiple solder joints per package/component are allowed.

The FATEVNT entry should only contain a single FATLOAD reference.