Solder paste deposition, usually the first step in most SMT PCB manufacturing processes, plays a critical role in the acceptability yield of the end-product PCB assembly. Due to the importance of this critical process step, inspection of the printed PCB substrate is vital prior to additional processing. The ability to detect solder paste bridges, skips and depleted deposits at this stage of the process will save a tremendous amount of end product rework time and labor. Depending on the complexity and density of the PCB substrate, unaided visual inspection of the solder paste deposits may not be comprehensive enough to reliably detect any solder paste deposit anomalies.

The use of manual optical inspection devices such as stereo microscopes, although beneficial, are not totally comprehensive and are a slow process at best. The recent introduction of automated optical inspection systems has proven to be very beneficial and cost effective due to their combination of speed and accuracy. Coupled with their speed and accuracy, the ability of these systems to measure, log and calculate solder paste deposits on a PCB substrate makes them an extremely valuable process verification and inspection aide.

Knowing the importance of the solder paste deposition process, the EMPF has incorporated into their SMT assembly line, automated in-line optical inspection capability for verification and measurement of PCB substrates printed with solder paste. The in-line inspection system uses high-resolution optical imagery to calculate vital statistics such as solder paste deposition height, total area of the solder paste deposition and volumetric measurements of the solder paste deposit. The ability of the system to calculate and store these measurements makes the system a valuable tool not only for inspection, but also for process development and control.

The versatility to inspect any PCB pad geometry, either square, rectangular or circular, ensures us the capability to reliably detect any solder paste deposit anomalies. The ability to calculate and log any measured variables in the solder paste deposits from one area of the PCB to another, provides valuable SPC data and ensures coplanarity of the solder paste deposits across the entire substrate. This will help to alleviate any potential solder joint irregularities. By inputting the length and width of the PCB pad and setting a reference point for height, the system will calculate height, area and volume of the solder paste deposit automatically and log this information into a database for later comparison. The ability to rapidly and reliably detect irregularities in the solder paste deposits, at this stage of the process, enhances the overall end product yield and reliability.

If you would like further information on Automated Optical solder paste inspection processes or any other process related to SMT PCB manufacturing, please contact the EMPF Helpline at 610-362-1320 or log onto the EMPF website @ www.empf.org