The joint strength and microstructure of fluxless Au/Sn solders in InP-based laser diode packages

Abstract

The joint strength and microstructure of fluxless Au/Sn solders in InP-based laser-diode packages after thermal-aging testing were studied experimentally and numerically. Specimens were aged at 150°C for up to 64 days. The joint strength decreased as aging time increased. The microstructure and fracture surface of the Au/Sn solder joints showed that the joint strength decrease was caused by both the enlargement of the initial voids and an increase in the number of voids as the aging time increased. Finite-element method (FEM) simulations of joint strength were in good agreement with experimental measurements. Both experimental and numerical results indicate that the enlargement of the initial voids and an increase in the number of voids, caused by stress concentration as the aging period increased, resulted in the weakness of joint strength. The effect of temperature-cycling testing on the power variation of the InP laser diodes using fluxless Au/Sn solders was also studied. It was shown that the laser diodes operated in the stable condition up to 500 cycles.

Microstructural evolution of the Au–20wt.% Sn solder on the Cu substrate during reflow

“…At present, a compromising method is to apply the specific Pb-free solder with the desired and beneficial characteristics to the specific packaging process. Eutectic Au-20 wt.% Sn solder (denoted as Au20Sn hereafter) is one of the commonly used solders in optoelectronic packaging [4][5][6][7]. This solder alloy has excellent fatigue and creep resistances and, in particular, can be applied through a fluxless bonding process [8][9][10].…”

Numerical Analysis on Thermal Tuning Efficiency and Thermal Stress of a Thermally Tunable SG-DBR Laser

“…The other structure parameters are same to that in [18]. In this study, to simplify the complex 3-D multi-physics coupling simulations, all the materials are assumed to be thermal linear elastic before they yield [20]. Materials properties including the density , the specific heat C, the thermal conductivity K , the ohmic resistivity R, the Young modulus E , the Poisson's ratio v and the coefficient of thermal expansion (CTE) are regarded as temperature-independent as listed in …”

“…As most of semiconductor materials are elastoplastic, we generally assume they are thermal linear elastic before yield [20]. In thermoelastic problems, taking temperature field into account, we numerically solve equilibrium differential equations, geometric equations and constitutive equations based on FEM and finally evaluate the thermal stress field.…”

Microstructure and failure mode of Sn–37Pb soldered in laser diode packages

“…The composition and microstructure changes in the solder material may change the mechanical properties of the solder joint. Sheen et al [24] reported ductile solder failure with cup and cone fracture-characteristics for their as-reflowed specimens. However, in our experimentation, brittle fracture was observed to occur within the LD for the as-reflowed specimens.…”

“…The geometrical complexity in an epi-side down bonded ridge-waveguide LD (see Fig. 1) and the multiple epitaxial LD structure may result in different failure behaviors [24].…”