ADS Layout Tutorial

Authors: Vipul Chawla and Dr. Dong S. Ha

4. Organizing a layout project using components

Instead of designing the whole layout in a single layout design file, it is smarter to organize the layout into a hierarchy of components and inter-connects. Creation of a component is similar to creating a new layout design. Use steps mentioned in step 2 to open a new layout window. In this tutorial we take an example of a 44 pin CQFP component. Footprint information is usually provided in device datasheet. An example footprint information is shown in figure 6. Footprint information usually contains among other things; pad width, length and pitch. From the footprint information given in figure 6, we can interpret that pad width is 16 mils and pad pitch is 31 mils. However, pad length is not provided. In this case pad length is taken long enough to accommodate the component easily.

Figure 6: Footprint information for a CQFP44 component.

By default ADS uses increments of 5 mils for placing and moving components. However, suitable increment size should be selected before starting a layout for ease of layout creation. For example clicking on Options ? Grid Spacing ? < .50-1-100 > selects an increment size of 0.5 mils, 1 increment per minor grid and 100 minor grids per major grid in both X and Y direction. A more customizable control of Grid/Snap size is available from Options ? Preferences, under the "Grid/Snap" section.

Assuming that the component is to be placed in top layer, select �cond� layer from layer selection window, then click on Insert ? Rectangle. An example rectangle creation is shown in figure 7.

Figure 7: Creating a rectangle in ADS.

In order to help with placement of various pads of CQFP44 footprint, rulers and construction lines can be used. These are available under "insert" option in ADS. An intermediate stage of CQFP44 component footprint creation is shown in figure 8. The figure illustrates use of construction lines and rulers.

Figure 8: Footprint of SO14 component with rulers and construction lines.

Figure 9 shows partial complete footprint of the component with all the pads placed. Note that we have added an outline of the component and have also indicated location of pin 1. These have been created in the layer "silk_screen" � the white colored marking on a PCB. Outline has been created using Insert ? Path and pin 1 marking has been created by using Insert ? Text.

Figure 9: Footprint of CQFP44 component with all the pads placed.

Lastly, we need to add solder mask to the component. This mask is used to define the portions of the layout where components pins/pads will be soldered. For the CQFP44 package footprint completed here, solder mask is needs to be added on all the pads. This can be easily accomplished by using the "Advanced Copy/Paste" function available in ADS. Select all the pads and click on Edit ? Advanced Copy/Paste ? Copy To Layer and choose "solder_mask" layer and hit OK. All the pads will be copied from "cond" layer to "solder_mask" layer, thus creating the desired solder mask. Completed footprint of CQFP44 component is shown in figure 10. Note that construction lines need not be deleted, as they are not visible when the component is instantiated in another layout. Once completed, the design should be saved. This is done by selecting File ? Save Design or File ? Save Design As and by entering the desired component name. All designs are saved in the "Networks" directory of the layout project.

Figure 10: Completed footprint of CQFP44 component.

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