Guideline to Setup an Effective Visual Inspection Process Part 2

With the advancement in automated visual inspection technology today, more and more high end technology product manufacturer are turning to the automated visual inspection solution.  Automated visual inspection could be more reliable than human inspection if it is set up properly.

Groundwork to set up a proper automated visual inspection process has to start even before the purchasing of the  visual inspection equipment.

Below is a set of guideline on how to set up an automated visual inspection process :- 

  1. Before acquiring an automated visual inspection equipment,  determine what type of product characteristics which required automated inspection
  2. Select equipment which is suitable to inspect the potential defect in the product and understand the limitation of the equipment.  For example if PCBA is surrounded by huge component,  there could be shadow effect and some equipment does not have the capability to make correct judgement. 
  3. Determine the percent coverage which could be inspected versus the total unit per piece part by the equipment.  For example if one Printed circuit board assembly has 2000 joints  and inspection equipment can only inspect 1500 joints,  the  percentage would be (1500/2000)X100% = 75%.  Identify which location  of the part that cannot be inspected by the equipment.
  4. Once the automated visual inspection is already acquired,  there must be a dedicated expert available to setup and calibrate the equipment properly base on clear operational definition. 
  5. Prepare a series of limit sample which consist of accept, reject and marginal accept and reject sample based operational definition. 
  6. After equipment is setup, use a series of prepared limit sample to calibrate the equipment to ensure that the equipment can accept or reject limit sample according to their actual accept or reject status
  7. It is recommended to do a repeatability study to ensure the equipment can reject or accept part according to the limit sample accept or reject status multiple times
  8. Once the equipment is properly set up,  all setting should be locked to prevent any unauthorized changes.
  9. Establish preventive maintenance procedure for the equipment to ensure the machine is always in good working condition.  Preventive maintenance could include cleaning machine and checking the lighting system.
  10. Usually a human verification is necessary to ensure the equipment judgement call is correct and the result should be used to fine the tune the equipment.
  11. Once all the setup is done correctly,  there must be a regular verification  conducted using limit sample to test the machine assessment results align the limit sample status pass or fail.

It is sad to say there are many companies that invested in the expensive automated inspection equipment but they never spend time to set up the equipment properly. I have seen good inspection equipment become a white elephant where its sole purpose is to impress customer.  There so many false calls that the operator just press the bypass button without even review the result on the display.
What I have written on visual inspection might be something simple,  however it is always overlooked  from my experience of working with more than 100 manufacturing sites all over the world.  Only a handful of  manufacturer made an effort to set up and qualify their inspection equipment properly.  Inspection is also a process by itself and we would like have a very consistent input such as man with operator training, method documented,  environment brightness being checked etc to ensure we have consistent output of correct judgement on the product is accept or reject status.

If  planning is done properly for an inspection process,  then we will have optimum return from the inspection process of screening out reject from reaching the end customer. There are even companies who blame their inspector for detecting high reject instead of be thankful!!!!

I had always challenge manufacturers to remove inspection process if it is not done correctly as it had defeat its purpose. Why should they be paid for process that is ineffective be it human or automated inspection.

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