The SMT assembly process is continuously challenged by the factors which enhance circuit board performance and limit productivity. The Pick and Place and Reflow systems reflect these driven issues by adding more and more controls to their systems, but the fact is one of the age old processes continues to operate within the same rules since the dawn of the SMT assembly world, SMT screen printing.
The industry created gate factors into the field of the SMT assembly to measure and weed out the process failures which don’t meet the process requirements. The SPI (Solder Paste Inspection) systems and AOI (Automated Optical Inspection) systems, although designed to help improve process controls, utilizing their data, have become increasingly more like an automated go-no-go screening system.
The SMT printer, a simple concept, introduce a board, stencil (designed to be a mirror image of the pattern of paste deposition required for the given board), correlate board to stencil positions and then raise the board to meet the stencil and print the paste/cream medium, using a predetermined process recipe, machine program. Separate the board from the stencil and send the board downline to continue the SMT assembly process. Given all the factors involved in boards and technology(ies), the printer environment is a major factor to control and affords us the opportunity to improve yields from the beginning of the SMT assembly process.
The increasing demand to miniaturize/economize these assembly processes is becoming a bigger challenge to all SMT assembly lines.
The manufacturing sites are seeking improved process controls, improving the EOL, End of Line, yields.
One such element which has seen recent changes and yielding good results is the stencil innovations, helping improve the Cp and CpK of the printer process and yielding impact to the EOL. The impact is relevant to the EOL results, required to expand our process window capabilities.