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:
  1. Leadless solder joint
  2. Ball Grid Array (BGA) solder joint


Figure 1.

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) Δ γ = C L D h s Δ α Δ T MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyiLdqKaeq 4SdCMaeyypa0Jaam4qamaalaaabaGaamitamaaBaaaleaacaWGebaa beaaaOqaaiaadIgadaWgaaWcbaGaam4CaaqabaaaaOGaeyiLdqKaeq ySdeMaeyiLdqKaamivaaaa@4411@
Where,
L D MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitamaaBa aaleaacaWGebaabeaaaaa@37BA@
Component length (PKGLEN field on the FATSDR entry).
α MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqySdegaaa@3793@
Coefficient of thermal expansion (CTE) (A field on the MAT1 entry).
h s MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiAamaaBa aaleaacaWGZbaabeaaaaa@3805@
Solder joint height. (PKGTHK field on the FATSDR entry).
Δ α = C T E p − C T E c MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyiLdqKaeq ySdeMaeyypa0Jaam4qaiaadsfacaWGfbWaaSbaaSqaaiaadchaaeqa aOGaeyOeI0Iaam4qaiaadsfacaWGfbWaaSbaaSqaaiaadogaaeqaaa aa@4201@
Difference between thermal expansion coefficients of the PCB and the component soldered onto the board.
T MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamivaaaa@36CD@
Input temperature.
Δ T = T p − T c MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyiLdqKaam ivaiabg2da9iaadsfadaWgaaWcbaGaamiCaaqabaGccqGHsislcaWG ubWaaSbaaSqaaiaadogaaeqaaaaa@3E17@
Difference between temperatures of the PCB and the component soldered onto the board.
C MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qaaaa@36BC@
Empirical model constant for solder fatigue (specified using the C4GAMMA field on the PFATSDR entry). It is equal to 1 2 MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaaca aIXaaabaWaaOaaaeaacaaIYaaaleqaaaaaaaa@3796@ 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) Δ W = 0.5 ⋅ Δ γ ⋅ F A s MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyiLdqKaam 4vaiabg2da9iaaicdacaGGUaGaaGynaiabgwSixlabgs5aejabeo7a NjabgwSixpaalaaabaGaamOraaqaaiaadgeadaWgaaWcbaGaam4Caa qabaaaaaaa@45CF@
Where,
F MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOraaaa@36BF@
Shear force.
A s MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqamaaBa aaleaacaWGZbaabeaaaaa@37DE@
Cross-section area.
The fatigue life is calculated as:(3) N f = 1 W p ⋅ Δ W MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOtamaaBa aaleaacaWGMbaabeaakiabg2da9maabmaabaWaaSaaaeaacaaIXaaa baGaam4vamaaBaaaleaacaWGWbaabeaakiabgwSixlabgs5aejaadE faaaaacaGLOaGaayzkaaaaaa@41D6@

Where, W p MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4vamaaBa aaleaacaWGWbaabeaaaaa@37F1@ 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.

Leadless Solder Joint

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.

Loading should be a static load with Thermal Expansion Coefficient defined.

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.

Loading should be a static load with Thermal Expansion Coefficient defined.

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. For a BGA joint, unless a single solder SET is defined, it is recommended not to define PKGLEN on FATSDR. PKGLEN is assumed to be the distance between the centroid of the package and the solder.

Outputs

General fatigue output for Damage and Life are supported.