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Why DFMA? Panelization SMEMA Fiducials CAD/BOM Formats Parts Pkging.

CAD and BOM Formats


The placement robots used at Logas require intermediate programming. This programming involves the conversion of x-y data provided by the client (as generated by their CAD software) to a format to be used by the robots’ database to execute placement. The process can take days depending on the density of the PCB (parts per board). Consequently, the data supplied will determine the level of programming required. The two scenarios described below amplify the programming nightmare experienced due to poor CAD data formatting.


a.                  Inconsistent Data: This is when a part occur in two or more locations on a PCB but are being assigned different package names:

                REF.ID   P/N         PACKAGE     X     Y     R

R1       RM1000      R0603       54    44    180

R2       RM1000      0603        65    77    90

The data ftip software will not complete the conversion. This is a control mechanism to minimize placement errors which may be in the form of placing a part in the location meant for another type of part but with similar package size.

The package name for part number 2 will be corrected to read R0603 for the program to run.

This will also create additional programming requirements. The database conversion program assumes that part numbers are unique. Hence, if a part occurs more than once on a PCB, each occurrence would be mapped to the unique part number. Therefore, if a part value is used to denote part number in the CAD program, the software will map package type to part value. It is common knowledge that two or more parts can have the same value, rating and tolerance but different package sizes.

Programming problems of the kinds described above introduce defects; since manual adjustments becomes necessary to prepare the CAD data in a format that the conversion software will accept. Consequently, the practice of adjusting CAD data impacts data integrity. Logas quality system does not allow for CAD data adjustment of this nature.

Clients are advised to assign their own unique part identifiers and to incorporate these into their CAD system. Common format could be in the form of the table below:

Ref.ID. Part No.   Package    x       y       r       Side

R1         RM1000       R0603           76    88    180    TOP

R2           RM1000       R0603           89    73    90      TOP

R3           RM1200       R0805           43    33    0         BOTTOM

C3           CA1000       C0603           80    44    0        TOP

C4           CA1302       C1206           26  10    90       BOTTOM


For the bill of materials (BOM), it is recommended that the same format be adopted as the one described above (use of unique part identifiers and differentiating package types).


Part No.  QTY Circuit Ref/RefID Description Mfg. P/N
RM1000 2 R1, R2 Res, 120k, 10V, 0603 ERO10276RC
RM1200 1 R3 Res, 10k, 20V, 0805 ERO00019RC
CA1000 3 C3,C6,C10 Cap, 1uF, 0.25W,0603 ECP17263CP
CA1302 4 C9,C12,C11,C14 Cap, 45uF, 0.12W,1206 ECP11001CP
Recommended Bom format...

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