VLSI - PRINTED CIRCUIT BOARD

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Getting Started with LayoutCompiled by Ryan Johnson

May 1, 2002

Open Orcad Capture under Engineering

Software

Under FILE, choose NEW, PROJECTThe following box should appear…To create a the circuit for your PCB,

choose PC Board Wizard.Choose where you will save it and

what you will call it.

Click OK

In the next box, choose if you want to

enable project simulation or not.

Click Next.

The next box allows you to choose which

libraries to include in the design. If

you do not choose the right ones now,

they always can be added from the

schematic.

Click Finish.

A blank schematic page will appear.

This is where you will draw your schematic that your PCB will be modeled after. Important: Notice that there is a PSpice menu on the menu bar. If this is not there, you will not be able to simulate your circuit.

RS2

1kV1

V2

12V

0

VEE

Q3Q2N2222

Q2Q2N2222

V

C1

5p

0

V3

-12V

RS1

1k

VDD

V

RC210k

out2

Q4Q2N2222

out1

RC110k

VDD

RBIAS20k

VEE

0

Q1Q2N2222

Draw your circuit and simulate it to make sure it does what you want it to.

Once you have done this, return to the project window.

The next step requires that the design file be

highlighted.

For Layout to create a netlist file that Layout can use,

Still with the design file highlighted select the following: Under the Tools menu:

Annotate

click OK,Design Rules Check…

click OK,Create Netlist

Under the first tab called Allegro, click off Create Allegro Netlist,

(Allegro is not installed on the computer at Calvin)Go to the Layout tab, check Run ECO to Layout. This allows continual

update between each program when changes are made.Click OK.

This completes everything that Layout will need to implement your circuit onto a PCB.

You can also create a bill of materials to see each part and how many you will need to construct the circuit.

Again, with the design highlighted, under the Tools menu, choose Bill of Materials.

You can check View Output File to see it.These last steps have created many output files that can all be selected and viewed from the

project manager widow under Outputs.

You are now ready to open Layout and implement your circuit into PCB. Open the program Layout Plus under the Engineering Software menu, PSpice, Cadence.

Under File, choose New. The following window will appear. This is where you choose what template you will put your circuit on. Ask your professor for the Layout Footprint Book that will show you what each template is. If you want to implement on a blank board, choose DEFAULT.TCH.

Next you need to load your netlist that you created with your circuit in Cadence. This can be found where ever you saved your circuit. Find it and select it.

Also, choose where you want to save your

PCB.

Next, layout will link your circuit to the PCB. Sometimes, your component footprints (the size, shape, and hole size for the component) will not be recognized or found. If

this is the case the following warning will appear followed by several options:

If you have the Layout Footprint Book and you know what shape and size the component will be, you can find one in the book and link it to the component

by choosing Link existing footprint to component.

The following window will appear where you can

select from various libraries, the component shape

that you want the component

to look like.

You can also create your own footprints by selecting Create or modify footprint library…

Once you have all your footprints, the components will appear in no particular order. You first need to define an origin by choosing Tool, Dimension, Move Datum.

Next, you need to place the outline of the board that you parts will fit on. Choose Tool, Obstacle, New. Place an outline that will fit each part inside it.

Next you need to choose which layers you will have on your board. If you are making this board at Calvin, you will probably only be using one side for traces. These means

that all other layers need to be removed. Go to Tool, Layer, Select from Spreadsheet…

Double click on the layers that you want to modify. In the window that pops up, click off the layers that you will not use (Choose Unused Routing).

Getting Familiar with the Toolbars

In order to modify the PCB, different toolbar buttons need to be engaged.

Zoom buttons are here:

To move a component, the component tool must be selected:

To move labels or text, the text tool must be selected:

Use this button to check the design rules:

(Errors on the PCB will be circled)

This button allows you to make your own connections:

Once you have your board outline or boundary defined, you are ready to place parts. Placement settings can be modified under Options, Place Settings.You can choose to place the board manually, or you can have the program do it is self.

To do it yourself, just make sure that the component tool on the toolbar is selected. Then you can move the parts yourself and place them where you want.To have the program do it for you, under Auto, go to Place, Board. The program will place each part within the boundary. If your boundary is too small, errors will appear when you run the Design Rules Check from the toolbar. (Important: Always make sure to check your

design rules after each modification

to the board.)

If you are not satisfied with the board placement or need to change the placement for any reason, you need to go to Options, choose Placement Strategy.

This will bring up a spreadsheet showing which passes have been completed.

The DONE needs to be changed in order to replace the board. To do this, highlight the passes that you want to redo, right click and choose Properties.

In the window that pops up, click off DONE, click OK. Next, under Auto, choose Unplace, Board. Now you are ready to re-place the board.

Sometimes it is desirable to get a certain look to your board. You can create groups of components that will be placed next to each other.

With your board Unplaced: Select the component tool from the toolbar. Highlight the components that you want to group. Go to Tool, choose Group, New.

In the window that appears, enter a Group number. Then, re-place your board. These components will be placed next to each other.

If at anytime, you want to only view certain layers of the board, you have to make the layers that you don’t want to see invisible. To do this, choose the layer that you don’t

want to see in the toolbar:

Then, under View, choose Visible<>Invisible. You will not be able to see this layer anymore. You can also to this by using the Color Settings button on the tool bar. Highlight the layers

that you don’t want to see, right click, choose Properties, Visible<>Invisible.

Once you have placed the board, you are ready to route the board. You can manually route the board by selecting the Add/Edit Route Mode button on the tool bar:

Also, make sure that the Reconnect button is not selected (this allows you to see the routing.) Highlight the wire that you wish to route. The program will not let you route the through critical areas Once you have routed the wire in an ok place, it will turn to a wide, red wire. You can unroute the board or a component under Auto, by choosing Unroute, Board (or Component).

Auto routing is usually much easier and faster. It can also be modified if you are not happy with the results. To auto route the board, under Auto, choose Autoroute, Board.

To change how the program routes the board, under Options, choose Route Settings.

Once your board is routed, make sure that you check the design rules.

Once you have the board how you want it to be, you need to create drill files.For the first file that the drill machine will read is called THRUHOLE.tap. To create this file (along with a Gerber file) under Auto, choose Run Post Processor. The Gerber file will automatically pop-up and the THRUHOLE.tap file will be saved in the same location that your layout file is saved.

PCB board manufacturers will use the Gerber file.

This is not needed for boards made at Calvin.

To change the Post Processor settings, under Options,

Choose Post Processor Settings.

Other reports that need to be generated include: a drill file that tells what size each hole needs to be and file that shows the coordinates of each component hole on the board.To create these reports, under Auto, choose Create Reports. The following window will pop-up. As you can see, there

are many reports that Layout

will produce. The two that are

vital to making boards

at Calvin include:

Cross References and Drills.

Select those and whether you

want to save to a disk or if you

want to view them (they will be

saved where you saved your

layout project). You are now ready to fabricate your PCB.