3.6 Starting layout in orcad  (Page 8/9)

The DRD layer is a documentation layer that contains a chart with all your drill sizes and their locations on the board. The problem is that two drills are using the same symbol. In this case it is the 14 mil drill and the 150 mil drill. To fix the problem, click View Spreadsheet and select Drills to view the drills spreadsheet.

You can double-click the Drill Size cell to adjust the Drill Properties . I suggest starting with symbol 1 for the 13 mil drill and incrementing from there. When you are done, you should have symbols 1 to 8 , and you will no longer get the error when you open your design.

There is one other thing that needs to be done with regard to drills. Some board shops have limitations on the sizes of drills. The board shop we are using for this project offers only 16 drill sizes . They have programs that will scan your Gerber files and automatically adjust the drill sizes for you, but to avoid any problems it is wise to give them files with the correct sizes in the first place. This way you can be sure that your board will be manufactured exactly as you send it. It is also a good practice to consolidate drills anyway. In this design, we might try to adjust the footprints so that the 34 and 35 mil drill sizes are the same. The board shop will only have to use one drill bit, and this will save money.

To change the drills, we must edit the padstack in the original footprint. The Drill Drawing layer can help you find which footprints need to be changed. For example, we can see that the PLD and TIL311 use 34 mil drills. This is not a valid size, but a 35 mil drill is acceptable. Open the Library Manager and use the padstacks spreadsheet to adjust the drill sizes ( DRILL and DRLDWG layers) for these two parts. The footprints you are adjusting should be DIP-14 and PLCC-44 . You may have to adjust several padstacks in each footprint. In addition, make sure that the clearances we defined earlier for each layer are still good (they should be). Finally, when making changes to footprints like this it is always good to check the datasheet to make sure that the part will still fit. You are only making very small changes of 1 or 2 mils, but it is important to check.

Once you have made a change to a footprint, and now you need to update the footprint in Layout. Open the components spreadsheet and find the PLD. Double-click to bring up the Edit Component dialog box. Click the Footprint button to show the Select Footprint dialog.

Choose the new footprint from your library (not the local cache) and click OK . Click OK again when asked for the Replacement Range . Do the same procedure for the TIL-311. When done refresh the display. Your drill chart should no longer show any 34 mil drills.

Do the same thing for the parts with 37 mil drills and the 39 mil drills. Adjust the 37 down to 35, and adjust the 39 up to 40. When you are done, you should have only 6 unique drill sizes.

F. An Orderly Silkscreen – Use the Text Tool to adjust the silkscreen. All text should be oriented in the same direction for readability. Silkscreen cannot overlap pads or vias (overlapping traces is OK). Change the Detail Grid to a finer setting if necessary. Reference designators should be placed as close to the part as possible. Polarity signs should be placed in the correct position.