Happy’s Essential Skills: Producibility and Other Figures of Merit

Estimated reading time: 9 minutes

Each factor that emerges from the ranking process is calibrated by assigning values from one to 100 as seen in Figure 6. The "1" factor are easy to manufacture and the "100" factor are impossible today but merely very difficult in a few years. In my example, the measure is “minimum drill diameter size” and values are assigned for 1-25-50-75 and 100.

Figure 6: The Factor Weighting Table is used to calibrate the ‘measured’ group from one to 100.

9. Create lLinear model for FOM

The resulting scoring equation will look like the linear equation below (sum of C_nFW_n) and would be used like this:

SCORE = (C1) (FW1) + (C2) (FW2) + (C3) (FW3) + (Cn) (FWn) + ....

For example, if we assume the producibility of a bare PWB may be scored with the above equation if the following factors were established by the F.O.M. Process:

               1. Size of the substrate      C1 = 1.5

               2. Number of drilled holes    C2 = 3.0

               3. Minimum trace width       C3 = 4.0

Where the proposed PWB design has:

               1. Size of the substrate      FW1 = 36

               2. Number of drilled holes    FW2 = 18

               3. Minimum trace width       FW3 = 31

The producibility score would equal:   (1.5 x 36) + (3.0 x 18) + (4.0 x 31) = 54 + 54 + 124 = 232    

As I sometimes tell people about the process, “It’s based on expert opinions, used over and over, but it is surprisingly accurate!”

References

1. Holden, H., “Wiring Demand,” CircuiTree, June 1998.
2. Holden, H., “First Pass Yield,” CircuiTree, Sept. 1998.
3. Holden, H., “Producibility,” CircuiTree, Aug. 1998.

Happy Holden has worked in printed circuit technology since 1970 with Hewlett-Packard, NanYa/Westwood, Merix, Foxconn and Gentex. Currently, he is the co-editor, with Clyde Coombs, of the Printed Circuit Handbook, 7th Ed. To contact Holden, click here.

• < Previous Page