The basic principle of virtual forming of SMT solder joints
The principle of SMT solder joint virtual forming technology based on solder joint morphology theory can be expressed as shown in Figure 6.7. The input is the preliminary parameters of the solder joint shape and the PCB, soldering solder, SMC/SMD and its pin types related to the solder joint shape, and various determined or adjustable process parameters; the main content is solder joint formation, welding Point stress and strain analysis and fatigue life calculation, optimization evaluation expert system and simulation of the actual process environment supporting the above three contents; the operation result will be various optimized parameter data and three-dimensional shape graphics in a reasonable form; it will be displayed during operation The change of the three-dimensional shape of the solder joints with the adjustment and correction of related parameters.
Solder joint virtual forming technology combines the solder joint shape predictive control and CAD method with computer three-dimensional modeling design and simulation technology; the solder joint shape forming process is dynamically displayed and displayed by the computer; the simple parameter modification and evolution of the solder joint shape CAD process It is a process dynamic correction that combines parameter correction and solder joint shape and graphics correction; the single correction of the solder joint morphology and structure parameters is evolved into a multi-parameter correction that includes the correction of solder joint forming and welding process parameters; and it is supplemented by computer virtual process environment reality and human The machine dialogue interactive operation interface and other technical means make it more oriented to the actual process; the corresponding software is an intelligent multi-parameter solder joint morphology simulation optimization software containing an optimization expert evaluation system.
The virtual solder joint forming technology is an extension of the CAD technology of solder joint morphology, but it treats both the optimized design of the solder joint morphological structure parameters and the optimized design of the solder joint forming process parameters, which is closer to the actual production. Solder joint shape CAD—generally takes the best ideal shape as the objective function, assuming that the process parameters (solder parameters, soldering temperature, etc.) are ideal values, and the design-oriented process is based on structural parameters (pad size, pin structure size, etc.) The optimization design of the solder joint shape; the virtual forming technology of the solder joint shape takes the practically reachable reasonable shape as the objective function, and is oriented to the optimization design of the solder joint structure parameters and welding process parameters. Therefore, it is a solder joint CAD technology based on solder joint morphology theory and in a virtual reality process environment.
When SMT solder joint virtual forming software is used to analyze the solder joint shape of plastic package ball grid array (PBGA) devices, the three-dimensional shape of the solder joint changes with the volume of solder. In the figure, V is the solder volume (mm3), and w is the maximum radial size of the solder joint (mm). In this example, the upper and lower pad sizes are fixed and equal. According to similar virtual forming and analysis, the relationship between the solder joint shape and various parameters can be obtained, and the finite element analysis model can be established on the basis of the formed solder joint three-dimensional shape graph, and the stress and strain conditions of the solder joint can be established. And life expectancy analysis.
