IPC9850_Surface Mount Equipment Characterization.pdf - 第44页
IPC-9850 Official Proposal May 2001 44 The different methods to measure the angle of the component are described below. D-2.2.1 Using 2 diagonal fiducials Take the angle of the line through the 2 diagonal fiducials and s…
IPC-9850
Official Proposal
May 2001
43
Appendix D
Suggested Methodologies for Measuring Components using an Optical CMM
D-1 Introduction
In the IPC-9850 standard the following components are used to prove the accuracy of placement machines:
• Glass QFP-100, QFP-208
• Glass BGA-228
• Real 1608C
• Real SOIC16
However it is not described how those components must be measured on the CMM machine. The center of the
components can be constructed in different ways. Every method has its own accuracy.
This report investigates the different methods to measure the components and the sensitivity of the estimate of the
center location of the component to measuring and component variances.
Finally a recommendation is given how the components should be measured.
D-2 Slugs (glass components)
The glass QFP-100, QFP-208 and BGA-228 are provided with 4 fiducials, one at each corner of the component.
There are several ways to construct the center and the angle of the component using 2 or all 4 fiducials.
D-2.1 Methods to measure the X- and Y-location of the slug
The different methods to measure the center location of the component are described below.
D-2.1.1 Using 2 fiducials
Measure two diagonal fiducials and take the average x and y
D-2.1.2 Using 4 fiducials
Method 1
Measure all fiducials and take the average x and y:
4
4
4321
4321
yyyy
y
xxxx
x
component
component
+++
=
+++
=
Method 2
Take the intersection point of two diagonal lines through the fiducials
D-2.2 Methods to measure the angle of the slug
2
2
21
21
yy
y
xx
x
component
component
+
=
+
=
IPC-9850
Official Proposal
May 2001
44
The different methods to measure the angle of the component are described below.
D-2.2.1 Using 2 diagonal fiducials
Take the angle of the line through the 2 diagonal fiducials and subtract the nominal angle (in this case the
component is square so the nominal angle is 45 degrees).
D-2.2.2 Using 4 fiducials
Method 1
Take the average of the angle of the two diagonal lines through the fiducials
Method 2
Take the angle of the line through the vertical midpoints minus 90 degrees:
Method 3
Take the angle of the line through the horizontal midpoints:
Method 4
Take the average angle of all “sides” of the component:
Method 5: Take the average of the angles of method 2 and 3
D-2.3 Simulation
By simulating measurement errors on the X- and Y-locations of the fiducials, the sensitivity of the methods above is
determined.
The measurement errors on the fiducials are assumed to be distributed with a standard deviation of 0.0005 mm.
Then 1000 measurements are simulated (using MS Excel). With those measurements, the x, y, and theta locations of
IPC-9850
Official Proposal
May 2001
45
the component are calculated with the different methods above. The mean and standard deviation of the center
location using the different methods is given in the tables below.
Using 2 fiducials
Table D-1 Mean and stdev using 2 fiducials (nominal means are: x=0, y=0, theta=0)
x
(mm)
y
(mm)
theta
(mm)
Mean 0.000 0.000 0.000
Stdev 62.10
-5
61.10
-5
243.10
-5
Using 4 fiducials
Table D-2 Mean and stdev per method using 4 fiducials (nominal means are: x=0, y=0, theta=0)
Method 1 Method 2 Method 1 Method 2 Method 3 Method 4 Method 5
x
(mm)
y
(mm)
x
(mm)
y
(mm)
theta
(mm)
theta
(mm)
theta
(mm)
theta
(mm)
theta
(mm)
Mean 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Stdev 42.10
-5
44.10
-5
62.10
-5
60.10
-5
174.10
-5
228.10
-5
230.10
-5
167.10
-5
166.10
-5
D-2.4 Conclusion
From the results above can be concluded that using 4 fiducials to estimate the center location of the component is
more reliable. From table 2 is concluded that the best methods to calculate x,y and theta are method 1 for x,y and
method 5 for theta.
So the glass QFP and BGA are recommended to be measured as follows:
Measure the X- and Y-location of the 4 (black) fiducials. Construct with these results 4 (white) midpoints at each
side of the component. The theta of the component is constructed by taking the average angle of the 2 lines. Taking
the average x and y of the measured fiducials determine the X- and Y-location of the component. Beware that this is
NOT the same as taking the intersection point of the 2 lines through the midpoints.
2
A
3
4 C
D B
1