Question

The dataset below is the observed number of defects from inspecting 25 successive wafers each containing n= 100 chips. Here the wafer is the inspection unit. (a) Create the appropriate control chart to control the data. (b) From the control chart, would you conclude that the process is in statistical control? (c) If any out of control points by Western Electric runs rule 1 are observed, assume they have assignable causes and can be omitted from control limit estimates. Create a revised control chart for the reduced data (d) What control plan would you recommend for Phase 2 future production? Wafer Defects Wafer Defects 1 16 14 16 2 14 15 15 3 28 16 13 4 16 17 14 5 12 18 16 6 19 20 11 7 10 20 20 12 21 11 9 10 22 19 10 17 23 16 11 19 24 31 25 13 12 17 13 14

Answer 1

Answer:

Given that:

The number of defects from inspecting 25 successive wafers,each containing n = 100 chips

(a) Create the appropriate control chart to control the data.

Here we use c-chart and

Addupallthe c values Mc C

UC Lc 3Vc

LCLc 3Vc

Mean of defects = 16

C

LCL 16 3* V16

LC=16-12

LCL=4

UCL 16+3 12

UCL=16 12

UCE28

Control chart is given as in the image

35 30 25 defects 20 mean 15 LCL 10 UCL | 5 0 1 3 5 7 11 13 15 17 19 21 23 25 un

(b) process is not in the control as wafer number 24 is out of control as its value is 31 and out side the UCL

(c) The revised control chart after omitting the wafer 24 whose value was 31

30 25 20 - defects 15 mean LCL 10 UCL 5 0 7 9 1 11 13 15 17 19 21 23 25 un un

(d)

mean of defects =\bar{c}}=15.375

LCL=15.375-3*sqrt(15.375)

=3.6117

UCL=15.375+3*sqrt(15.375)

=27.1383