PFATSDR

Format

Definition

Comments

1. C4GAMMA is used to calculate the strain range of the solder joint in DIFFCTE method:
   $$\text{Δ}\gamma =C\frac{L_D}{h_s}\text{Δ}\alpha \text{Δ}T$$
   Where,

   $L_D$

   Component length.

   $\alpha$

   Coefficient of thermal expansion (CTE).

   $h_s$

   Solder joint height.

   $\text{Δ}\alpha =CT{E}_p-CT{E}_c$

   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). It is equal to $\frac{1}{\sqrt{2}}$ for leadless joint type. For BGA type, you can define the empirical model constant.

   Refer to Solder Fatigue Analysis for additional information.

2. K1 and K3 are dependent on the modeling of solder joints such as the thickness of solder joint interface layers and the creep constitutive model. Therefore, K1 and K3 are not material constants. Units of dimension for K1 and K3 should be consistent with those of length and stress on FATPARM. Dimension of K1 is cycles/stress^K2. The dimension of K3 is (length/cycle)*(1/stress^K4). For example, if length units and stress units in FATPARM are mm and MPa respectively, the units of K1 and K3 should be cycles/MPa^K2 and (mm/cycle)*(1/MPa^K4), respectively.
   The constants are used in the following equations to calculate life (N) of a solder joint:

   • Crack initiation:
     $$N_0=K_1\text{Δ}{W}_{ave}^{K_2}$$
   • Crack growth:
     $$\frac{da}{dN}=K_3\text{Δ}{W}_{ave}^{K_4}$$
   • Life:
     $$N=N_0+\frac{a}{\raisebox{1ex}{$da$}\!\left/ \!\raisebox{-1ex}{$dN$}\right.}$$

   Where, $\alpha$ is the joint diameter at the interface defined FATSDR.