From Ece

Senior Design PCB/Assembly Resource Page

This page contains resources on Printed Circuit Board (PCB) tools and assembly techniques that have been collected from various people and places for use by senior design students. Send questions to reese@ece.msstate.edu .

PCB Tools

PCB tools that I have had personal experience with are:

• Cadence ORCAD Capture (schematic capture) and Layout Plus (PCB) design (on ECE machines, available from Programs - Cadence PSD 15.0)
• 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.

Things to avoid in PCB Tools

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.

ORCAD Capture/Layout Plus Resources

• 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.

EAGLE Layout Editor Resources

• 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.
  • ZIP Archive
  • Library file for parts
• 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
  • Library file for parts

• 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 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.

Other Tools

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.

Footprints

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.

PCB Fab Services

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.
• Sierra Proto
• 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.

Surface Mount Rework Station in Senior Design Lab

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.

How do I prototype with surface mount devices?

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.

Misc Links

• PCB Design , a good site that has several tutorials on different aspects of PCB design and assembly.
• 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.
• Tutorial on Surface Mount stenciling
• Tutorial on Surface Mount Reflow
• Discussion of different PCB Finish types
• Tutorial on using Eagle to make GERBER files