00193407-02 HWWS SIPLACE Machine Accuracy EN.pdf - 第8页

© Siemens AG . . Änderungen vorbehalten SIPLACE Placement Systems Placement Accuracy What does a statement of placement accuracy +- 50 um at 4 sigma mean? The 4 sigma limit value of the no rmally distributed deviation of…

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© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
how do we define the capability indices?
¾ is it an approximate or exact estimation of the number of defects???
¾ is it a comparison of specifications??
¾ is it a question of interpretation?
example pick & place head Siplace 80F
sigma Cm; Cmk accuracy defect rate
±
1
68,27% 0,33
±
12,5
μ
317300
±
2
95,45% 0,66
±
25
μ
45500
±
3
99,73% 1
±
37,5
μ
2700
±
4
99,994% 1,33
±
50
μ
60
±
5
99,99994% 1,66
±
62,5
μ
0,6
±
6
99,9999998% 2,00
±
75
μ
0,002
which one is better??
50 µm / 4 sigma ⇔ 60µm / 5 sigma
it‘s not visible at the first view !!
Machine Capability
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
Placement Accuracy
What does a statement of placement accuracy +- 50 um at 4 sigma mean?
The 4 sigma limit value of the normally distributed deviation of the placement position is 50 um.
This enables the user to rate the reliability of the placement process.
The defect probability at 4 sigma is 60 ppm. The user can assume that placement error exceeds
50 um for only 60 out of one million placed components.
Limit value: 37.5 um (3 sigma) 2600 ppm
50,0 um (4 sigma) 60 ppm
75,0 um (6 sigma) 0.002 ppm
During this process, it becomes obvious that identical placement accuracy can be described in
different ways. The statements 50 um at 4 sigma, 25 um at 2 sigma and 75 um at 6 sigma are
equivalent, the standard distribution = 12.5 um.
Factors influencing placement accuracy:
¾ placement machine
¾ tolerances and twist of the PCB
¾ dimensional accuracy of the components
¾ bending of component pins
¾ ..........................
Machine Capability
© Siemens AG . . Änderungen vorbehalten
SIPLACE
Placement Systems
turn around point
standard
deviation
1 sigma
-1s-2s
+2s
+1s
m
turn around point
Machine Capability