Severity Reduction by Product or Process Design Change? Seeking Good Example

[brutas]

Please help, I need a good example of Severity reduction by product or process design change. It would be great to see examples for both cases.

My filed is microelectronics. Our processes are focused on testing (probing of wafers and final test of assembled devices).

My coleagues always ask for good examples and I cannot explain correctly.
What do you think about this case:
Process Function/ Requirements: Assure reliable recognition of the probed dice (legible and centered ink dots)
Potential Failure Mode: Recognition is not reliable (some ink dots are illegible)
Potential Effect of Failure: Rejected dice processed at Assembly house
Severity=8
Cause: Equipment malfunction (inker defect)
O=3
Prevention: Preventive maintenace
Detection: During WAK (visual)
D=7
Action: Switch to inkless probing

This is a change in a process: switching from ink probing to inkless (software marking) but I think this reducess the Occurrence not Severity...

Can you give me an examples for common processes like Packagin, Storage, Shipping?
I urgently need both cases - reduction of Severity through product or process design change

Thank you!

 

[mariav_66]

Re: Good example for Severity reduction by product or process design change?

Hi Brutas,

If you can reduce the occurrence or detection level that will reduce your RPN number and it is OK, the severity level in most of the cases can't be reduced.
Your current RPN number is:
8 * 3 * 7 = 168

If you reduce your occurrence level to 1 your RPN number will be:
8 * 1 * 7 = 56

This is a good improvement but for example if you reduce your detection level to 2 then your RPN number is:

8 * 1 * 2 = 16 Excellent!

 

[jeffrey_Chang]

Hi Brutas,
In your case, you have replace the inking process by using the wafer map (inkless) and thus you have actually designed out the failure mode, a redesign of the process. Hence, the severity of the failure has been eliminated, inkless means no more ink dot illegible problem.
As such, I think you have already provided an excellent example of severity reduction. However, with wafer map, you've other sets of problem and risk that you will need to address.
thks.
jeffrey.