ECEN 1400 - Introduction to Digital and Analog Electronics

Peter Mathys, Spring 2014


Making a Printed Circuit Board

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Overview

The goal of this webpage is to give a step by step description of how to create a printed circuit board (PCB) design in Ultiboard from the following Multisim schematic.

Count59module schematic

The hierachical block Count59_002 is a synchronous 2-digit counter with enable and set inputs that counts from 00 to 59 and then back to 00 and the schematic looks like this.

Count59_002 hierarchical block schematic

The end product (2'nd version with some corrections) looks like this.

Count59module PCB layout, V.2


Preparing your Schematic

To simulate a circuit in Multisim all that is needed is a SPICE model. For a printed circuit board layout it is necessary to specify real components which have specific physical properties like a length, width, height, distances between pins, etc. Most of this specific information is contained in the footprint of real (as opposed to virtual) components. In Multisim schematics virtual components are shown in black while real components are shown in blue. To verify and/or change the footprint of a component in a schematic, double-click on the component and then select the "value" tab as shown below for a virtual 10 kohm resistor.

Count59module, select 10 kohm resistor

The footprint entry at the bottom is empty for a virtual component.

Count59module, properties of virtual 10 kohm resistor

Click on "Edit footprint..." and then on "Select from Database" to get to the "Select a Footprint" menu.

Count59module, select a footprint

The choices are bewildering, there are some 5000 different footprints in the master database. Click on "Filter" and enter the following two filtering criteria (or something similar) to narrow the choices down.

Count59module, filter criteria for selecting a footprint

The most suitable footprint for through-hole 1/4W resistors is the Generic RES0.25 footprint shown below.

Count59module, select Generic RES0.25 footprint

Now the value tab under the properties of the resistor looks as follows.

Count59module, 10 kohm resistor with RES0.25 footprint

In the schematic the real resistor with footprint is indicated by the blue coloring.

Count59module, real 10 kohm resistor R1 with footprint

The same thing needs to be done for the 0.1uF bypass capacitors in the Count59_002 schematic.

Count59module, select virtual 0.1uF capacitor

Selection of footprint filter criteria for 0.1uF capacitor.

Count59module, filter criteria for 0.1uF capacitor

The best footprint match for the 01.uF bypass capacitors is the Generic CAP1 footprint.

Count59module, Generic CAP1 footprint for 0.1uF bypass capacitor

Now the value tab under properties of the 0.1uF bypass capacitor looks like this.

Count59module, CAP1 footprint for 0.1uF bypass capacitor

Now the schematic for the Count59module circuit should look like this (all resistors in blue).

Count59module schematic with real resistors

And the schematic for the hierarchical block Count59_002 should look like this (all bypass capacitors in blue).

Count59_002 hierarchical block schematic with real capacitors


Component Placement

After assigning footprints in Multisim to all components, the next step is to transfer the design from Multisim to Ultiboard. Click on "Transfer" and select "Transfer to Ultiboard 11.0".

Count59module, Transfer to Ultiboard

The transfer occurs in the form of a netlist which is a file with extension .ewnet. Save the file in a convenient location.

Count59module, Netlist Transfer to Ultiboard

The netlist imported to Multisim looks as follows.

Count59module PCB, Netlist imported to Ultiboard

Click on "OK" to import the netlist. Next you will see an empty board (with default size 6.3"x3.94") with all the components lined up outside the board.

Count59module PCB, Empty board with components ready to be placed

The components are typically placed by hand. The yellow lines are referred to as a "rat's nest" and show the connections that need to be made between the components. The goal is to place the components in such a way that interference between them is minimized and the rat's nest is as untangled as possible. Start by selecting one component (click on it) and placing it on the board, e.g., U2 as shown below.

Count59module PCB, Placing component U2 on the board

Gradually move all the large components onto the board and place them in suitable locations.

Count59module PCB, Main components placed on the board

Next, place the remaining smaller components. Make sure that the 0.1uF bypass capacitors are uniformly spread across the board and close to the power supply pins of the logic circuits.

Count59module PCB, All components placed on the board

Sometimes it is worth interchanging the placement of some components, e.g., U4 and U5 were interchanged in the placement shown below.

Count59module PCB, Components U4 and U5 interchanged

Usually one tries to as little board space as possible. After the basic placement is done you may want to move components closer together as shown below.

Count59module PCB, Components placed and moved closer together


Routing the Connections

The next step is to interconnect the components according to the netlist. This replaces the yellow lines of the rat's nest with copper traces. Ultiboard use 10 mil (1/100 in = 0.25 mm) wide traces by default. This is fine for signal lines like the clock, enable, load, etc. But the resistance of such a narrow trace is too large for the power supply connections and any other connection where a larger amount of current flows (e.g., to the LED displays).

Count59module PCB, Net properties in spreadsheet view

Count59module PCB, Change tracewidth to 30 mil for power traces

Count59module PCB, Start autorouter

Count59module PCB, All connections routed, DRC alert

Count59module PCB, Check design rule error

Count59module PCB, Design rule error fixed

Count59module PCB,

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Netlist Checking and Updating

--- To be completed ---


Creating Gerber Files

Count59module PCB, Select export to create Gerber files

Count59module PCB,

Count59module PCB,

Count59module PCB,

Count59module PCB,


Submitting the Gerber Files

Important: Before submitting the Gerber files of your PCB design check that all connections between components are made correctly. In particular, check that all integrated circuits have power supply connections.

A local PCB manufacturer is Advanced Circuits in Aurora, CO.

Count59module PCB, Advanced Circuits Website

They have a student program where you can order a single 2-layer PCB of up to 60 sq inches with a turn around time of 5 days.

Count59module PCB, Advanced Circuits Engineering Student Program