Design Rules
RULE 1: USE ZERO-WIDTH CLOSED POLYLINES

No matter which CAD system you use, it is important to draw filled areas using zero-width closed polylines. This means you should draw a boundary exactly where you want it to be filled, without compensating for the line width used to draw the boundary. In AutoCAD, use the "close" command to ensure the boundary (polyline) is completely closed. Although some CAD systems, like AutoCAD, only display the contour of the bound area, areas drawn using zero-width closed polylines will appear as filled on your pattern. If you are using AutoCAD, you can also use SOLID entities to draw filled areas. This method has the advantage of AutoCAD filling the solid's interior, providing a better display for you
RULE 2: CLOSE OPEN BOUNDARIES

Filled areas are typically enclosed by a series of zero-width polylines. For example, the drawing on the left includes a polyline with straight line segments and another with an arc segment. To fill the interior of the drawing, you need to join these two polylines and create a single zero-width closed polyline.
RULE 3: NO SELF-INTERSECTION

A polyline must not self-intersect, as this leads to unpredictable results. However, a polyline can touch itself, creating a re-entrant boundary. This technique can be used to draw filled areas with holes, as shown in this drawing...
RULE 4: DRAWING ISLANDS & HOLES
Islands and holes are clear areas within a dark pattern. A common mistake is to draw the island as a figure surrounded by the metallized area. This approach fails because the outer area will cover the hole

The designer drew the figure [A] expecting to get figure [B]. Instead, the mask came back as in figure [C]. The mistake was that the inner polygons were covered while filling the outer polygon.

There are several methods for creating islands and holes in a drawing. One approach is to create separate layers for the outer and inner polygons. The most effective technique, however, is to use composite layers, where data from one layer can be added to or subtracted from data on another layer.

The second method involves using two separate drawing items and snapping them together. You can create two separate boundaries that align to form the frame. However, ensure you use a closed polyline, as using lines can often result in an incorrectly linked, self-intersecting boundary.

The third method is to use a re-entrant boundary. To create an island, you enter the interior of your polygon and exit via the same path. This technique, known as a re-entrant boundary, is best executed using a closed zero-width polyline.
PLEASE SEE THE MENU COMPOSITE LAYERS FOR MORE INFORMATION
RULE 5: USE BLOCKS
A typical pattern might contain hundreds of donuts, solid rounds, or solid rectangles. While you could draw each one individually in AutoCAD, there's a more efficient method: using the Block command for each element. In AutoCAD, define each figure as a block and use the center of the figure as the block's reference point. Assign a short name to each block. Then, use the block insert command to place the blocks in the appropriate positions.
RULE 6: DRAWING ERRORS TO AVOID.
- Extraneous lines that touch the boundaries. These are detected by the post processor and may affect your photo-mask. These are extremely hard to see if they are covered by another larger line.
- Figures insides of figures: The larger outer figure will cover up the inner figure
- Boundaries that self intersect
- Hatching - this is a visual aid only, and will not appear in the DXF file
- Truetype fonts - again, this is not supported by DXF files. All fonts must be compiled into SHX fonts before using them. Enclose any SXH fonts newly compiled along with your data.
- Do not use Scale or Rotate within blocks. This is not supported
- Don't use AutoCAD's trace entity.
- If your drawing contains unused layers and blocks, erase these layers/blocks and purge the drawing file to eliminate the extraneous data.