Ahne, Victor, et al.,

Check the numbers below.  Are they supposed to be 0.2 sigma, 0.3, etch?  I think 3.0 sigma means 27 defects (or nonconformances, if you want to use a non-pejorative word) per ten thousand.

My understanding from ~1989  was that the defective fraction at six sigma was predicated upon a shift of the mean of a normal distribution of 1.5 sigma from the center of a tolerance range. The defect fraction was thus greater than would have been if the distribution were centered within that range.

The tale of the bags of good and defective parts, with what may have been different numbers, I heard at that time, but thought it likely apocryphal.

What appears to be the colloquial meaning of six sigma now is social rather than mathematical.  Louis Hart

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahne Oosterhof
Sent: Monday, August 24, 2015 1:08 PM
To: [log in to unmask]
Subject: Re: [TN] PWB, PCB End Of Line Shorts/OPENS detection/Test

.2 Sigma: 308K errors per million (69% accuracy).             30 errors per
100
.3 Sigma: 66.8K errors per million (93.3% accuracy).          6 errors per
100
.4 Sigma: 6.2K errors per million (99.4% accuracy).             1 error per
200
.5 Sigma: 233 errors per million (99.97% accuracy).            1 errors per
5000
.6 Sigma: 3.4 errors per million (99.999997% accuracy).    1 error per big
number

In the past a good number was '3-sigma', or 6 errors per 100. This company ordered 100 parts from Japan and required meeting a '3-sigma' error rate. So they got the batch back with 100 parts in the package, of which 6 rejects were in a separate bag. (They were obviously telling: we can do better than
3 sigma.)

Today in many instances companies strive to meet '6-sigma', not always successful yet. And even  with excellent process control, including excellent incoming inspection it remains very difficult.

Copied:
""Although one of the key concepts of Six Sigma is to strive for near perfection, the practical goal of Six Sigma programs is to continually improve the rate of accuracy as it approaches that nearly perfect goal. As the quality control of an enterprise progresses, it traverses lower sigma levels that have less accuracy. Six Sigma, however, is not just a measuring stick for performance, nor is it a technique for improving performance: Six Sigma as we know it addresses corporate culture and seeks to change it into an environment that is at every point optimized for quality.
Six Sigma, therefore, is an attempt to unify all employees of a corporation into a unified team that works together to produce high quality goods and services.""

Yet it still is very difficult to get circuit boards at low sigmas, especially if you are using fine pitch components.
Good yields come from everyone paying attention and doing the right thing correctly.
 
Ahne.

PS: When Motorola started pushing for '6-sigma' somebody explained to me why such an effort was important. His example: say a nurse handles babies all day. How many times is she allowed to drop one? 3-sigma? 4 sigma? 5 sigma? 6 sigma? 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Monday, August 24, 2015 5:38 AM
To: [log in to unmask]
Subject: [TN] PWB, PCB End Of Line Shorts/OPENS detection/Test

Fellow TechNetters:

   In today's world of High Volume Production.   What is a good YIELD Rate.
Back some 30 years I remember 89 to 92% yield depending on board complexity.
Our AOIs weren't as good and accurate as todays.   I need some kind of warm
and fuzzy number.   We used to put external image numbers on all boards to
help sort repeat images printing anomalies.   What happened to the PERFECT
COUPON that was to HELP solve these type of issues.

   I also see frequent Front to Back cores misregistration!!!!!   What's up
with that anomaly.

Victor,


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________