Convection Soldering Research Articles

Effect of voids on thermo-mechanical reliability of chip resistor solder joints: Experiment, modelling and simulation

With the introduction of lead-free solder alloys, the effect of voids on solder joint reliability has rapidly gained importance. In this study, a first analysis of X-rayed CR0805 solder joints shows a significant reduction in void content, from 20% down to 2.5%, after vacuum soldering. The statistical analysis of the void distribution demonstrates that the vacuum option reduces number of voids and median diameter of voids in comparison to the convection soldering process. A subsequent accelerated thermal cycling test of these analysed test vehicles, according to JESD22-A104D, indicates the tendency of a higher characteristic life time for higher void content. In contrast to these findings, the 1% to failure criterion reveals a higher reliability for lower voiding. During the finite element method (FEM) modelling part of this study, two modelling approaches of void implementation into solder joint geometry are investigated: modelling with a constant volume of the standoff for different void contents, and a modelling approach with a random combination of void content and volume of standoff. The modelling approach with the random combination reveals that voids can reduce the lifetime in the “worst case” parameter combination. In particular, the 1% time to failure rate indicates a quantitative correlation with the experimental results. Furthermore, the FEM results suggest a higher impact on reliability for a single void in comparison to a distribution of multiple voids with similar void content. Finally, the FEM study shows a high sensitivity of predicted life time with respect to the standoff height. Based on this finding, the CR0805 solder joint geometry is examined using optical inspection and cross-section polishes with the outcome that the better wetting behaviour during vacuum soldering causes a reduction of the solder alloy volume and consequently further decreases the standoff height.

Characterization of solder joints made with VPS on DBC substrate

Ensuring the best quality of the solder joint can be crucial in assemblies which operate in different environmental conditions, since the reliability of the whole circuit depends on the quality of the joint. Solder joints on a ceramic substrate can be more prone to cracking because of the higher stress generated in the metal layer than is the case with simple FR4 substrates. In addition soldering methods like vapour phase soldering or convection soldering can have a significant influence on the solder joint’s mechanical quality because of the thickness of the intermetallic layer, the number of voids, solved intermetallic compound and precipitations in the joint. Solder joints from a SAC305 (96.5 %Sn3 %Ag0.5 %) alloy were prepared on DCB substrates which have Al2O3 as the base material which is covered by a Cu wiring layer and an Ni/Au solder preservative coating. Three different soldering methods were used, vapour phase soldering with and without the vacuum option with convection reflow soldering as a reference. The solder joints were studied by shear strength measurements, 2D and 3D X-Ray computed tomography to evaluate void formation. The fracture surfaces and cross-sections of the joints were studied by optical and scanning electron microscopy to compare the microstructural differences of the joints. The tests carried out showed the particular relationships between the mechanical strength of the solder joints and the applied soldering technology in the case of DCB substrates.

Mathematical Modeling of Mechanized Technologies Soldering

The possibility of compliance with the required technological soldering conditions and ensuring their reproducibility for wave soldering, laser soldering, convection soldering have been researched. Comparing the experimental data to the results of mathematical modeling allowed selectng optimal modes of the wave, convection and laser soldering of electronic devices. The conclusion about the prospects of the analytical dependencies to improve mechanical soldering of electronic devices for any purpose. When heating by convection or wave solder, the temperature along the depth of the solder joints is less than when the contact or laser soldering. It was found that the temperature of the solder joints with infrared and laser soldering can be estimated based on the heat equation for a semi-infinite plate with a given heat flow on the surface. Warming up of the printing unit and, consequently, the solder joints when soldering, convection can be described by equations of the regular mode.

Simultaneous lead and lead-free convection soldering from Rehm Thermal Systems

Simultaneous lead and lead-free convection soldering from Rehm Thermal Systems