In the last section, we have demonstrated to how we can build a square via of the same shape as the via pad. You may wonder how we can build a cylindrical via. This section will demonstrate to you how we can build cylindrical vias. The square is of size 5 by 5 mils. We would like to build a cylindrical via of radius 1.5 mils at the center of each square via pad. We will take the square via structure bridge1.geo as our starting point.
Broken polygons at Z = 10 for connection
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Step 1 Open .\ie3d\samples\bridge1.geo. Select Edit->Select Polygon Group command. Check the 3D Polygon layer on the Layer Window to gray state. Check the No.2 Layer Z = 10 and the No.3 Layer Z = 12. You should get the Layer Window to what is shown in Figure 4.27.
Step 2 Window the bridge as shown in Figure 4.27. Only the 3D polygons are selected while the 2D polygons on Z = 10 and Z = 12 are not selected. This is because of the gray state of the 3D Polygon layer in the Layer Window (Please read the Appendix AT for detail).
Step 3 Select Edit->Delete command to delete the selected 3D polygons. The via pads and other 2D polygons are still in the MGRID window (see Figure 4.28).
Figure 4.28 The bridge1.geo structure after the 3D polygons are deleted.
Step 4 Save the file as: .\ie3d\samples\bridge1a.geo. We will use it later when we demonstrate how we can build conical vias.
Step 5 We are going to create some polygons on some fictitious layer to representing the cylindrical vias first. We will use the via pads on Z = 10 to create the polygons.
Select Edit->Select Polygon Group command. Check No.2 Layer at Z = 10 and un-check all other layers. Window the bridge as shown in Figure 4.27. You will see only the two via pads at Z = 10 are selected. Select Edit->Copy command to copy the selected squares at Z = 10 into the clipboard. Select Edit->Paste to paste the two squares from the clipboard. You will see the shapes of the two squares are following the mouse when you move it.
Step 6 Click some where at the window. MGRID will prompt you the Copy Object Offset to Original dialog. Please enter the X-offset = 0, Y-offset = 0 and Z-offset = 50. It means that we want to copy the two squares to some where at the same (X, Y)-location. However, we want its Z-coordinate to be 50-mils larger or at Z = 60 mils. Change the After Paste option from “All Objects De-Selected” to “Only Pasted Objects Selected” (see Figure 4.29). Select OK to continue. MGRID will copy the two squares at the same (X, Y)-location and Z = 60 mils (see Figure 4.30).
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You will notice the two copied squares are being selected. In case you forgot to check “Only Pasted Objects Selected”, the two copied squares will not be selected. You can use the
Edit->Select Polygon Group command to select them for the next steps.
Figure 4.29 The Copy Object Offset to Original dialog.
Figure 4.30 The two squares at copied at Z = 60 and the same (X, Y) location.
Step 7 We are going to select the shapes of the square at Z = 60 to create the shapes of the cylindrical vias. The shape of each cylindrical via is of circular shape. On IE3D, we will model a cylindrical via as a polygonal via. When the via’s size is electrically small, we can use ribbon via or square via for it. Normally, it is very accurate to use hexagonal or octagonal via to model a circular via.
In this example, we will try to use hexagonal via for it. We want to create the hexagons first.
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Select Adv Edit->Convert Polygons in Shape command. The Convert Polygons dialog comes up. Select the “No.1 …” in the list box. Make sure the Converted Shape is “Circle”. Change the Radius to 1.5. Enter Segments/Circle = 6. Enter the Circle Start Point = 0 (see Figure 4.31). You will see MGRID is updating the information in the “No.1 …” item in the list box while you are entering the parameters.
You may enter “Start Point” much when you use many of the commands related to circular shape. Basically, we are using a polygonal shape to model a circular shape. There is a question where the angle of the start vertex is at. We define the “Start Point” as the fraction of one division angle for the polygonal shape in approximating the circular shape. The Start Point = 0 corresponds to that the 1st vertex is at an angle of 0 degree. The Start Point = 0.5 corresponds to that the 1st vertex is at an angle of 50% of one division (see Figure 4.32).
Figure 4.31 The Convert Polygons dialog after you define the parameters for the 1st shape.
(a) Start Point = 0 (b) Start Point = 0.5
Figure 4.32 The difference between different Start Points for circular shape.
Step 7 Click at the Same Shape button in the Convert Polygons command. MGRID will update the shape information about the No.2 polygon with the information defined for the No.1 polygon while it will not change the center location of the No.2 polygon. Basically, we want to have the two rectangles converted to hexagons of the same shape at their individual center locations.
Step 8 Select OK. MGRID will convert the two rectangles into hexagons as shown in Figure 4.33. We are going to use the hexagons to build the vias between Z = 10 and Z = 12.
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Step 9 Select Edit->Select Polygon Group command. Check the Z = 60 layer in the Layer Window only. Window the two hexagons to select them. Select Adv Edit->Build Holes and Vias from Selected Polygons. The dialog comes up.
Figure 4.33 The two rectangles at Z = 60 are converted into hexagons.
Figure 4.34 The Build Holes and Vias from Selected Polygons dialog after you enter all parameters.
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There are many different options for the Build Holes and Vias from Selected Polygons dialog.
There are three schemes to build the holes: (1) Circumscribed Rectangle Scheme”; (2) Cutting Overlapped Polygons Scheme; (3) Meshing Alignment Scheme. The Circumscribed Rectangle Scheme has been the scheme used before IE3D 11. It is very robust. One shortcoming is that it relies upon a circumscribed rectangle to build the hole. Then, we try to duplicate the shape of the polygon inside the circumscribed rectangle. If the polygons where we are building the whole shape into cannot cover the circumscribed rectangle of the selected polygon, it may create extra polygons we do not want. Another shortcoming is that it cannot preserve the division lines of the polygons we want to build the hole.
To overcome the above limitations of the Circumscribed Rectangle Scheme, we have introduced the Meshing Alignment Scheme. It is a very powerful scheme. Normally, it can build the holes cleaner than the Circumscribed Rectangle Scheme while you can have the option to Keep Divisions on Filled Hole. It was implemented in IE3D 11 and it is now very reliable and robust.
It is the default scheme to be used.
You have the option to “Clear the hole” or “Fill the hole”. Basically, MGRID builds a hole of the same of a selected polygon on a specified layer added into the list. If you choose “Clear the hole”, MGRID will the hole only and it will not fill the hole after it creates it. If you choose “Fill the hole”, MGRID will fill the hole with the polygon shape. You have the choice to Keep Division Lines on Filled Holes. This option is useful when you are building vias on both sides of a layer. You may apply the Build Holes and Vias from Selected Polygons command twice to the layer: Once for the via connection from above to the layer and the 2nd time for the via from you still want to keep the selected polygons after you use their shapes to build the holes.
When you checked or added more than one Z-coordinate to the list for holes, MGRID will activate the option for you to “Build vias between holes on different layers”. Since we are building vias using this command, we should check it.
Step 10 By default, the layers z = 10 and 12 are listed but not checked. Please check the Z = 10 and Z = 12 layers. If necessary, you can select Add button to add new values the list. Now, the “Build vias between holes on different layers” option is activated. Check it. We will get the dialog exactly as shown in Figure 4.34.
Step 11 Select OK to continue. MGRID will build the cylindrical vias as shown in Figure 4.35. It is what we want.
The Build Holes and Vias from Selected Polygons command is very powerful and it is frequently used in the IE3D for Boolean operations. You should practice it more and learn its power. It will help you much in building vias and interconnects in complicated structures.