Design Rules

RULE 1: USE ZERO-WIDTH CLOSED POLYLINES

photomask layout creating boundaries

No matter what CAD system you use, the import thing is to try and draw filled areas using zero-width closed polylines. In other words, draw a boundary in the exact position that you would like to be filled, and do not compensate for the line width that is sued to draw the boundary. In AutoCAD, use the close command to completely close the boundary (polyline). Areas drawn using zero-width closed polylines appear as filled areas on your pattern, even though some CAD systems, such as AutoCAD, only display the contour of the bound area. If you are using AutoCAD, you may also use SOLID entities to draw filled areas. This has the advantage that AutoCAD fills the solids interior so that it displays better to you.


RULE 2: CLOSE OPEN BOUNDARIES

Open polyline

Filled areas are often bound by a series of zero-width polylines. For instance, the drawing to the left consists of a polyline with straight line segments, and a polyline with an arc segment. If you want to fill the interior of the drawing, you need to join the two polylines, and create a single zero-width closed polyline.


RULE 3: NO SELF-INTERSECTION

photomask layout creating boundaries

A polyline may not self-intersect. If it does, the result is unpredictable. A polyline may, however, touch itself. This is called a re-entrant boundary, and it can be used to draw filled areas containing holes, as in the drawing below...


RULE 4: DRAWING ISLANDS & HOLES

Islands and holes are areas of clear pattern surrounded by dark pattern. A very common mistake is to simply draw the island area as a figure surrounded by the metallised area. This is not going to work as the outer area will cover the hole

Drawing islands and holes

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.

photomask layout creating boundaries

There are a couple of different methods for creating Islands / Holes in the drawing. The first method is to create a separate layer for the outer and inner polygons. And the most powerful technique is to use composite layers. The data on any layer can be added or subtracted from data on another layer

photomask layout creating boundaries

The second method is to use two separate drawing items and snap them together. You can use two separate boundaries that butt up against each other to form the frame. However, only use a closed polyline – because if you use lines, most likely they will be linked incorrectly to form a self intersecting boundary.

photomask layout creating boundaries

The third method is a re-entrant boundary. This method to realize an island is to go into the interior of your polygon and out again via the same path. This is called a re-entrant boundary and is best done using a closed zero width polyline.

PLEASE SEE THE MENU COMPOSITE LAYERS FOR MORE INFORMATION

RULE 5: USE BLOCKS

The typical pattern may have hundreds of Donuts, Solid Rounds or Solid Rectangles. While you could draw each one on AutoCAD as a donut or circle, there is a more efficient way. The trick is to use a Block command for each element. In AutoCAD, you can define each figure as a block and then use the centre of the figure as the reference point of the block. Give each block a short name. Using the block insert command, insert the block at the appropriate position.


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.