Sorry for my lately reply, let me clarify the dark spot problem. UTL has earnestness to find out the darkest groove on returned units for measurement the laser mark depth. However, the sampling units are within laser mark depth specification but UTL still finding another unit which have the deepest laser mark depth for setting up as a master unit for vision system.
Based on current UTL's procedure, UTL measured the laser mark depth at crossing point and darkest point. So, "4" letter was chose to measure because those point are darkest groove and crossing of letter.
Machine: High power scope (Model: Smartscope)
Method : UTL measured laser depth distance at Z height axis under high power scope 200x magnifier.
1.) Focus on compound surface and set Z height to be 0.
2.) Focus on darkest marking groove ("4" letter).
3.) Read the laser mark depth value.
When UTL received 3 returned units from Spansion, UTL will measure the laser mark depth for these 3 units per the specific point circled as you mentioned by using microscope with 100X magnification. After these 3 returned units were performed the cross section at the circled point. So, UTL will update the root cause, corrective action and preventive action in improvement report. The evidence of actions in D5-D7 as attachment file.
If you have any concern, please let me know.