It is usually a good idea to use computer simulation tools such as OrCAD PSPICE to verify your circuit designs before you spend time prototyping them. This can help you catch errors without wasting valuable time in the lab. Not all circuit components are modeled in OrCAD, but some many extra SPICE models and tips may be found at the SPICE Simulation Resources page.
To get your PCB fabricated, you must do the following:
Hold a Schematic Check Party:
This is done as a team. You get in one room, display the schematic, and do the following (do this before checking the PCB):
For each wire, have a team member explain the wire function.
For each unique component type, bring up the datasheet of the component and check the pin number against the pin function and ensure they match.
For each component, drag the component around a bit and ensure that all wires 'rubberband' with the component, ensuring that the component is connected.
Hold a PCB Check Party:
This done as a team. You get in one room, display the PCB layout, and do the following
Once the board is autorouted, use the "Tool>DRC" check that your board has no design rule errors. If there are errors, fix them. If you tell Eagle to 'ignore' the errors, then you need to be sure that the error can actually be ignored (check with the instructor or TA).
Print out the top copper on a piece of paper, and ensure the components all match their footprints in terms of size
For each unique footprint, ensure the pad number of the footprint matches the component pin number on the datasheet
For each connector on the PCB, ensure that its placement and orientation is correct
Submit the PCB files to me:
use www.freedfm.com to check your PCB for manufacturing problems. If you are using the Eagle software, download this eagle_gerber.zip archive that shows the gerber files you need (top copper, bottom copper, top soldermask, bottom soldermask, top silkscreen). Use the ".cam" file in the archive as the 'job' file to generate the Eagle gerbers. If you are using ORCAD, download this orcad_gerber.zip archive that contains the equivalent files (look at the ORCAD tutorial on the PCB page on how to generate these gerbers). If you are using Altium Circuit Maker, this page gives what files to generate for the www.freedfm.com check.
There will almost certainly be one or more errors on your board. Plan for this by placing a couple of 'empty' headers (whatever you have room for, 5- pin, 6-pin, 10-pin, whatever) on the board so that you have some 'holes' that you can use for patching if necessary.
Before submitting the board for fabrication, plot the top and bottom copper layers on the printer (make sure it prints to scale), and place all of your parts on the this 'fake' PCB to make sure the footprints match what you have and that you do not have any spacing problems with components. This requires you to have ALL of your parts before you submit your PCB.
Have a team session and manually trace out each NET on the PCB before you submit it to try to ensure that there are no silly mistakes.
Once the PCB is returned, populate it only a little bit at time and test what you have populated. Generally, it is power supply first (voltage regulator + caps, followed by the microcontroller, followed by the remaining subsystems).
SPEND some TIME on your silkscreen so that it is very descriptive! You will be glad that you did when you populate the board. For all headers, label each individual pin, and always clearly mark 'pin 1' of the header. You may need to use the 'smash' command in Eagle to separate component names/values from their component so that they can be moved around/rotated/placed in order to be readable.
MAKE A BETTER PCB -- this is a good tutorial from Sparkfun on some rules for making a better PCB within Eagle - I guarantee that if you even just follow one half of these recommendations that you will have a better PCB.
In addition to PCB fabrication costs, there are also costs involved with assembling the board. If you are trying to estimate these costs for presentation or business plan purposes, there are many places on the web that you can use. Two are listed below, both can give online quotes:
Advanced Assembly (ww.aapcb.com) -- uses automated assembly, much cheaper if mostly surface mount.
Screaming Circuits (www.screamingcircuits.com) -- uses hand-assembly, will be more expensive, but no much difference between surface-mount or through-hole.
For these services, you need to know how many through-hole/surface mount components are on your board. From Eagle, open your design and use "File>Export>Partlist" and write the parts to .txt file (you can then import this into a spreadsheet for counting purposes).
PCB tools that I have had personal experience with are:
Altium Circuitmaker - a powerful tool; free. This page gives what files to generate for PCB submission.
The Cadence PCB tool used in ECE Advanced Electronics (this tool has changed over time and so is no longer documented here, refer to your Advanced Electronics notes).
EAGLE Layout Editor from CadSoft Online
Both of these tools offer a schematic capture tool that is linked to a PCB tool so that consistency checks can be done between schematic and layout. Both offer autorouters for PCB layout and a reasonable number of component libraries. Both have about the same learning curve in terms of how to use the schematic capture and PCB tools. Neither can be learned overnight or in a single session. I would estimate that in probably three to five intense sessions (about 10-15 hours) with the tools in doing a typical senior design board, that you can become proficient in their use. Both of the tools run under Windows; there is a Linux version of EAGLE.
The ORCAD tool has no restrictions on board size, and can do multi-layer PCBs. However, you must be connected to the University network in order to check out a license from our license server. The ORCAD tool also has an auto-placer which can be useful if you design has many components. The ORCAD tool is available on the MSU ECE PC lab machines; you can also get the installation CD's by talking to the ECE system admin.
The EAGLE layout editor has an advantage in that there is a freeware version available that can do two layer designs (top/bottom) up to 4 x 3.2 in, and the schematic editor can only create one sheet. However, the auto router is included, all libraries are available, and there is no limit on component count. There is no license checkout in the freeware version so you do not have to be connected to the network. The GUI does not follow 'Microsoft norms' so the learning curve is a bit steeper than it would be with other Windows tool. We also have also purchased the professional version of Eagle with multiple licenses for those that require larger boards, talk to the senior design instructor about obtaining access to this.
There are other 'free' PCB tools available on the WWW. Please avoid those that only offer a PCB layout tool without schematic capture or that are tied to a particular PCB fabrication service. PCB layout tools without schematic capture are little more than drawing tools that let you put down PCB footprints and then have you manually draw traces between vias. While the learning curve on these types of tools is small, you will eventually wish that you spent the time to learn a tool that had more power or those that output files that are compatible with multiple PCB fabrication services.
Eagle Manual PDF
This is a simple board design by Wes Reeves that uses several of the newer components in the lab, like surface mount RS232 drivers, etc. Please note that this board isn't real; it only exists to give you a design using the new surface mount parts that you can copy from.
Library created by David Moak that contains some surface mount parts, including a PIC18 in a TQFP package. Library file.
Schematic Tutorial on EAGLE CAD, Layout Tutorial on EAGLE CAD, Creating Footprints on EAGLE CAD at Spark Fun Electronics
The CAM jobs gerb274x.cam and excellon.cam will produce correct Gerber files and a drill file. These should be the same as the default files; they're listed here just in case you edited either of them and would like to revert to the originals.
Tutorial on creating a custom part.
Common Errors in Eagle Layout:
Using the same width trace for both signal traces and power traces. The default trace width is 10 mil. Your default power trace width should be at least 15 mil, and 20 mil is better. To create a power traces of wider than default width, in the schematic editor use 'Edit>Net Classes" and create a new net class called 'power' and assign it a default width. Then, in the schematic editor, select a power net ('i' selection), and change its net class to 'power'. When this net is routed in the PCB, it will have the default trace width for that class.
Autorouter does not route all nets. When you click on the autorouter tool, a setup window appears. Change default routing grid from 50 mil to 10 mils and your design should complete during autoroute (if it does not, talk to the instructor for other hints).
Mixing manually-routed and auto-routed signals on a PCB:
If you find that you have a significant number of manually routed traces (typically high-current traces), then add some common tag into every signal name that is auto-routed (i.e., mysignal_ar, where '_ar' is the tag for auto-routed signals). This allows you to use the command 'ripup *_ar' command to rip-up all auto-routed signals and leave the manually-routed signals undisturbed.
A simple ORCAD Capture and Layout Plus tutorial - shows you the basic steps of creating designs in Capture and Layout plus; this is a good starting point if you have no previous experience with these tools. PDF, ZIP Archive.
A more complex tutorial on OrCAD Layout Plus - shows you the files necessary for PCB submission, how to use copper pour, and how to enter new footprints. This is appropriate if you are already familiar with OrCAD Capture and want to learn more details about Layout Plus. PDF , ZIP Archive .
This is a sample board design that contains a PIC18F242 and which supports the lab experiments in Micro I (ECE 3724). It is a two-layer, through hole design, and contains a library (MICROLABPKGS.LLB) that contains some custom footprints for things like a pushbutton switch, IR receiver, mini-jack, etc). ZIP Archive . This board was fabbed through PCB Fab Express with good results (the only minor problem was that the vias on the 5-pin SIP headers were a little too small). This board used copper fill for ground on both the top and bottom layers. I did this board in a hurry; if I had to do it over again I would add labeling on the top silk screen for each pin brought out to a header.
ORCAD is installed on the ECE PCs in the PC room on the first floor of Simrall. You can also obtain installation CDs from Michael Lane, the ECE system administrator whose office is on the first floor of Simrall next to the PC lab. However, to run the software you must be physically connected to the ECE network (a wireless connection will not work) in order to check out the necessary software license.
There are many, many other companies which offer evaluation versions of PCB tools. Some are listed below.
CADSTAR , has an evaluation version limited to 300 pins, 50 components, supports auto-routing.
CircuitMaker2000, has a 30-day evaluation version.
AutoTRAX EDA, a low-cost Schematic Editor/PCB tool. Autoroute requires clicking on each trace.
Freeware PCB, requires manual routing.
PROTEL PCB, design packages widely used in Australia
Mentor PADs, has an evaluation version.
Express PCB, offers free software for doing PCBs compatible with their fabrication service, must do PCB routing manually.
TopLine Dummy Components has data sheets for all commercial PCB footprints. If you are trying to determine the dimensions of a footprint, or just figure out what it looks like, take look at this site.
The Othermachine Othermill is a desktop PCB mill for rapid prototyping. Using the Othermill you can have a board milled in a matter of hours vs. weeks, this is useful for prototyping your board or even using the board in your final design. You will need to have Eagle installed on your computer as the Othermill works with Eagle .brd files.
Here are a few of the many PCB fab services available.
PCB Fab Express, five boards for about $90, one week turn-around time.
Advanced Circuits, one board for $33, one week turn-around time. Two routing layers, includes solder mask and top silk screen, up to 60 square inches
BatchPCB offers PCB service for $5/sq in in quantities of just one board; turn around time is significant. An offshoot of Sparkfun.com.
Express PCB, offers free software for doing PCBs compatible with their fabrication service, must do PCB routing manually.
PCBEx, five board for $78 for a one-week turn.
If you would like to reflow solder your surface mount PCB, order the board and other components as normal. In addition, you will need a stencil. This can sometimes be added onto your PCB order or ordered separately from OSH Stencils. Contact the TA to arrange a time to use the solder reflow oven. The TA will guide you through the process, but it is helpful to have watched the following videos first.
For the surface mount rework station and soldering station in the senior design lab:
A temperature of 400 for the hot air rework seems to work fine for IC packages. For surface mount discretes, you may want to lower this to 350.
One school of thought for solder iron temperature is "hot and fast", i.e., make the iron very hot so that the solder flows instantly and be quick about the work. In this case, use a temperature of between 450-550. If you use a copper fill for ground on your PCB, you cannot use much less than about a 450 temperature as the copper fill acts as a heat sink.
Leave the soldering iron tinned before you leave the station. Coat it throughly with solder before leaving; this helps to protect the tip.
There are three ways of prototyping with surface mount devices:
Glue the part on its back with its leads sticking up, and then solder-tack wire wrap wires to the legs. This is really only feasible for small pin count devices.
Buy a breakout PCB board that converts the surface mount package to a DIP package (see Breakout boards at Sparkfun Electronics ). This is probably the best alternative - the breakout boards are not that expensive. This requires you to solder the surface mount part to the PCB breakout board, then either solder header pins or wires to the breakout pads.
Buy a surface mount to DIP socket - these are fairly expensive - Digikey has some of these for sale.
PCB Design , a good site that has several tutorials on different aspects of PCB design and assembly.
Tutorials on Surface Mount Soldering -- very complete
A tutorial on PCB design by David L. Jones . Has a good discussion of solid design practices, definitions of terms.
Tutorial on Surface Mount Soldering using a thin-tipped soldering iron. This RealPlayer Video Segment shows how to solder an 80-pin surface mount part using a standard soldering iron in about 1 minute. This assumes a solder-reflow finish on the PCB (this means that the pads already have thin layer of solder on the leads). However, if your board has a solder mask to prevent bridging (which it probably will), then you can manually tin the pads with solder before applying this technique.
Introduction to Surface Mount , the last few slides of presentation shows how to perform Rework and Hand soldering for surface mount components.
Surface Mount Discretes (Caps, Resistors) , shows different sizes, has dimensions.