AOl basic principles and application advice

1. A person observes an object by judging the amount of light reflected back. Most of the reflected amount is bright, and less of the reflected amount is dark. AOl is the same as human judgment. The basic principle of AOI inspection is to use artificial light source LED light instead of natural light, optical lens and CCD instead of human eyes, and compare analyze and judge the amount of light source reflected from the object with the programmed standard.

2. Application of AOI and problems to be improved

(1) Application of AOI

A. AOI is placed after printing, it can perform process inspection on the printing quality of the solder paste.It can check whether the amount of solder paste is too much or too little, whether the position of the solder paste pattern is shifted, whether there are bridges, tipping, leakage printing between the solder paste patterns,

B.AOI is placed after the placement machine and before welding. Can check component misplacement, component shift, component reverse (such as resistance flip) component side, component loss, wrong polarity, excessive pressure caused by the bridge between solder paste patterns, etc.

C.AOI is placed after the reflow oven. Welding quality inspection can be used to check component misplacement, component displacement, component reversal (such as resistance flipping), component loss, wrong polarity, solder joint wetness, excessive solder volume, too less solder volume, missing soldering, virtual welding defects such as s bridging, solder balls (balls between pins), component uplift (tombstone)

(2)Problems to be improved in AOI

A. AOI can only perform visual inspection and cannot completely replace online inspection inspection (ICT).

B. Invisible solder joints such as BGA. CSP and flip chip cannot be inspected.

C. It is also necessary to use a side CCD for PLCC for more accurate inspection.

D. Some lower resolution AOIs cannot be used for OCR character recognition check.