Designing Your Own Device: Mask Design Rules

Masks for generating the molds for soft lithography are commonly designed using AutoCAD and then printed onto transparencies films. The following are design rules you should follow when preparing your microfluidic circuit before submitting it to Stanford Microfluidics Foundry. Also, be sure your design follows the Basic Design Rules.

Mask Specifications


1. Start by using the mask template provided. This template corresponds to a 4" diameter silicon mold size (recommended size).


2. AutoCAD files should be submitted to the foundry in .dwg format using the version AutoCAD 2000, 2004, or 2007.


3. Ensure that AutoCAD is set to the correct internal units before beginning your design. Under the menu Format -> Units, ensure the following settings:

Length Type: Decimal, Length Precision: 0.0000

Drag-and-drop Scale: Microns


4. Masks can be printed at :


40 000dpi => recommended minimum feature size 10um


5. Each mold (i.e. control and flow) is drawn in a separate AutoCAD layer. If you are creating hybrid molds where you have multiple photoresist heights on a single mold, each photoresist height must be drawn in a separate layer.


6. The AutoCAD file which you submit to the foundry must have all layers in one single file. The layers should be drawn and overlapping as corresponding to your design (you should not separate out individual layers in different areas of the workspace).


General Layout


1. Try to fit in as many devices as possible onto a single mold. However, ensure there is enough space between chips for adequate bonding and to enable the PDMS to be cut into individual chips (see Basic Design Rules).

2. Leave a ring of approximately 0.5cm free around the mold perimeter. This area should be void of any design or critical chip area since photoresist uniformity is least reliable around the perimeter of a wafer.

3. Each layer should have lines or right angle corners indicating where the PDMS should be cut around the perimeter for the devices. Make these cut lines approximately 50um wide.

4. Masks are printed on 8.5" x 11" transparency sheets. Therefore, a total of four molds in four quadrants can fit on each sheet. If you have several chip versions which do not fit onto one mold, design a second mold in another quadrant.


Labeling


1.All layers should have text labels clearly identifying:

Your Name
Date
Mold Name
Layer Name (for mulit-height molds, there will be multiple layer names for each mold)
Project Name
Version Number

All these labels should be within the perimeter of each mold. The height of the characters in the labels should preferably be such that the letter "L" is at least 650um high, if space is available.


2. Polyline-based text can be created by copying and pasting (and scaling appropriately) individual characters from either one of these files: alphabet.dwg (AutoCad 2004 format), or alphabet.dxf (AutoCAD R12 format). You can also use the linetext AutoLisp application to draw text (instructions on how to use the application are in the linetext-readme.txt file included with the application).


3. If you have several chips of different designs on one mold, label each chip by a different name or number, i.e. Chip1, Chip2, etc.


Feature Specifications


Alignment Marks


Mask Alignment Marks for Multi-Height Molds

Device Alignment Marks for PDMS-PDMS Alignment
Several alignment marks should be placed around the device area.