While SMT AOI machine can be used at multiple locations on the SMT production line to detect specific defects, AOI inspection equipment should be placed in a location where the most defects can be identified and corrected as early as possible. There are three main check locations:
After the solder paste is printed
If the solder paste printing process meets the requirements, the number of ICT defects can be significantly reduced. Typical printing defects include the following:
A.Insufficient soldering tin at stencil printer.
B. Too much solder on the solder pad.
C. Poor coincidence of solder to solder pad.
D. Solder bridge between pads.
In ICT, the probability of defects relative to these situations is directly proportional to the severity of the situation. Slightly less tin rarely leads to defects, while severe cases, such as fundamental tin, almost always lead to defects in ICT. Inadequate solder may be a cause of component loss or open solder joints. However, deciding where to place AOI requires recognizing that component loss may occur for other reasons that must be included in the inspection plan. This location inspection most directly supports process tracking and characterization. Quantitative process control data at this stage includes printing offset and solder volume information, while qualitative information about printed solder is also produced.
Prior to reflow oven
The inspection is done after the component is placed in the solder paste on the board and before the PCB is fed into the reflow furnace. This is a typical place to place the inspection machine, as most defects from solder paste printing and machine placement can be found here. The quantitative process control information generated at this location provides information on the calibration of high-speed chip machines and close-spaced component mounting equipment. This information can be used to modify component placement or indicate that the mounter needs calibration. The inspection of this location meets the goal of the process trace.
After reflow soldering
Check at the end of the SMT process, which is the most popular option for AOI, because this is where all assembly errors can be found. Post-reflow inspection provides a high degree of security because it identifies errors caused by solder paste printing, component mounting, and the reflow process.
Post time: Dec-11-2020