Throughout the manufacturing process, many issues can arise that would delay the completion of your PCB. You have ensured an efficient fabrication process by setting Design for Fabrication (DFF) constraints based on your manufacturer’s specifications, but what about the assembly process? By setting Design for Assembly (DFA) constraints, you can catch potential issues in your design that would be troublesome in the assembly process, such as incorrect spacing or pastemask errors. OrCAD PCB Designer Professional uses visual indicators to flag these issues in real-time as you design, saving you time by correcting the design as you go instead of after completion. This tutorial will show you how to use and configure the Design for Assembly constraints included in OrCAD PCB Designer Professional, to ensure your board can be efficiently assembled. If you would like to follow along with this tutorial, you can download the design files here.
Step 1: Open your design in OrCAD PCB Designer Professional and open the Constraint Manager by selecting Setup→ Constraints from the menu.
Select the Manufacturing Tab in the Worksheet Selector section of the Constraint Manager.
Expand the “Design for Assembly” (DFA) tab to view the available constraints.
Step 2: Create a Constraint Set (CSet). Select the Outline Worksheet under “DFA Constraint Set”.
Click in the “New CSET” Column. Set the following information:
- DFAOutlineCset: Etch_Top
- CSet Usage: Etch
Set the following values for the Etch_Top Constraint Set:
- Component to Outline: 1.524
- Component to Cutout: 1.524
Step 3: Create a Constraint Set (CSet). Select the Pastemask Worksheet under “DFA Constraint Set”.
- DFAMaskCSet: Mask_Top
- CSet Usage: Non-Etch
Set the following values for the Mask_Top Constraint Set:
- Pastemask to Pad: 98
- Missing Pastemask: On
- Pastemask to other mask types: 0.025
Step 4: Assign the Constraint Sets. Select the Outline Worksheet under “Design”.
In the “Referenced DFA CSet” Row, assign the Etch_Top Constraint Set to the TOP Assembly Layer.
Select the Pastemask Worksheet under “Design”.
Expand Primary→ Pastemask Layers. Assign the Mask_Top Constraint Set to PASTEMASK_TOP.
Close out of the Constraint Manager Window.
Step 5: Place Component “U1”. In the Options Tab, Check the box next to “U1”.
Click to place the component. Purposely place the component too close to the outline of the board.
Step 6: View the Outline DRC Errors. Place the curser over the DRC Marker to view more information.
Step 7: Move the Component. Click on “U1”. Click to place the component farther away from the board outline.
The DRC Error has been resolved and the DRC Marker is no longer visible.
Step 8: View the Pastemask DRC Errors. Place the curser over the DRC Markers to view more information.
Step 9: Modify the Design Padstack. Right click on any of the pins in U1 and select Modify Design Padstack→ All instances.
Select the “Mask Layers” tab in the Padstack Editor.
Change the Diameter of Pastemask Top to 0.4.
Step 10: Update the design. Select File→ Update to Design and Exit.
The DRC Errors have been resolved and the DRC Markers are no longer visible.
Outline: Checks minimum spacing between components and the design outline or cutouts.
PkgToPkg Spacing: Checks package to package spacing with different DFA rules assigned based on the board stack-up. This constraint is for use in Rigid-Flex Designs.
Spacing: Checks spacing from component body to pins, holes and edge fingers. Checks pastemask to pastemask and pastemask to via spacing.
Pastemask: Checks annular ring of pastemask to SMD copper pin pad, missing pastemask and pastemask to mask openings.
By utilizing constraints for common assembly issues, you can detect and correct any potential pitfalls DURING your design process. Ensure efficient manufacturing and minimize delays in assembly with Real-Time Design for Assembly in OrCAD PCB Designer Professional.