While there is great satisfaction in home building PCBs, adding up the cost of the blank PCB, etchant and the drill bits comes to over $4 per board. But for $6.25 a board the whole thing can be made professionally. This Instructable takes you through the steps to create the Gerber files that the PCB manufacturers need. The total cost was $75US including shipping for 12 boards. 3 boards would be about US$62.
This Instructable builds on some great work at http://www.instructables.com/id/EXU9BO166NEQHO8XFU
(Draw Electronic Schematics with CadSoft EAGLE) and http://www.instructables.com/id/EZ3WN1QUKYES9J5X48
(Turn your Eagle schematic into a PCB). Eagle is free.
Step 2: Place all the components
The instructable links on the intro page show how to create a pcb from a schematic using EaglePCB. One main difference is that none of the design rules about track widths need to be changed at all (the drc design rule check). The defaults are all fine and while the tracks look really thin and close to pads it doesn't matter as the green solder mask makes it very easy to solder. In fact, these sorts of boards are much easier than soldering up prototypes. Some big pads were used for connecting external wires and there were a few extra comments added for the white component overlay layer.
The wonderful thing about having boards like this made compared with building homemade boards is you don't have to worry about trying to optimise the autorouter for a single layer. Just run the autorouter once and it defaults to double layer mode and it always produces a 100% design automatically within a few seconds. Even with components a lot denser than this board Eagle always autoroutes the whole board.
Step 3: Fix any errors
Sometimes one finds a better component in the library or changes a component. To rip up and replace the tracks click on the ripup symbol (green circle), click on the traffic light (red circle) and then reroute (yellow circle).
Over the last few years I've found a few tips and tricks to making better boards:
1) To get tracks closer - Tools/Auto/General and set the grid to something like 10mil
2) To make data tracks thin but power tracks fatter, Edit/Net (at the bottom) and start typing in a text box to name the class. I use three classes; Gnd, Power and one for all the rest.
3) In DRC, distance/copper dimension change from 40 to 20 - this allows two tracks to fit between IC pads, which can greatly increase board density.
4) In DRC - clearance/pad to via increase from 8 to 40. (leave all the rest at 8mil). This increases the distance between vias and pads so less chance of bridges when soldering. Surprisingly, this also sped up the autorouter too.
Step 4: Create a drill file
The manufacturer needs to know what drills to use. Eagle has automatically used whatever drill fits the components that have been chosen. Go to File/Run and select the file "drillcfg.ulp". I selected inches rather than mm and that seemed fine with the manufacturer. Click ok then ok again. It will save a file with a .drl extension.
Step 5: Create an Excellon drill data file
Click File/Cam Processor
Step 6: Open the Cam Processor
In the Cam Processor click File/Open/Job
Step 7: Select the Excellon File
Step 8: Click on Process Job
Click on Process Job. This will create some files. Close down this menu with the x at the top right.
Step 9: Create the Gerber files
Repeat steps 5) and 6) to reopen the CAM processor and this time open the file gerb274x
Step 10: Create the Gerber files
This is the important bit. You need to click on each one of the tabs circled in green and ensure that Mirror (circled in yellow) is off. As you click through the tabs you will notice the Nr and Layer lines highlighted on the right will change. One default you might want to change is component values - in my copy this was deselected and the silk screen ended up with U20 but not the actual chip - eg an IC might be 74HC04. Click along the tabs to Silk Screen Cmp, and click on 27 tvalues. Once all the mirror boxes are definitely unchecked, click on Process Job (red circle).
Step 11: Collect all the files and Zip them up
I collected 10 files, put them in a temp directory and used winzip to create a single zip file. I have a feeling that one or two of these are not actually needed by the manufacturer but I sent them anyway. The file the manufacturer definitely does not need is the .sch schematic file.
Steps 4-11 are summarised in text format at http://drvernacula.topcities.com/creating_gerber_files_from_eagle.htm
Step 12: View some of the files just to make sure
Download a free Gerber file viewer
Step 13: View a Gerber file
The drill files can be viewed with a text editor.
The Gerber files can be viewed with a free Gerber file viewer. I went to the website above and installed Viewmate. It appears in the Start menu of windows as Start/Programs/Pentalogic. In Viewmate I clicked on File\Open and browsed to C:\Program Files\EAGLE-4.16r2\projects\RadioRepeater and at the bottom of the windows changed Files of Type to *.*. As an example this is the .sol solder side file
Step 14: Find a PCB manufacturer
This company OurPCB is in China and stood out from some of the others in that they freely advertised their price for small quantities. Shipping is FedEx and to the US they quote $22. The $40 above for a 10 sq inch board is for all the 3 boards, not per individual board. At a quantity of 100 the price per board is $1.80 each. They can give a firm quote once they get the zipped files.
These boards arrived in 9 working days. There were a few problems initially with me sending the wrong files (which is mainly why I wrote this Instructable!) and they were very patient and polite from their end. There were also some email problems in that emails coming back were totally blank. I was able to read the source text and at least work out who they were from but I nearly did delete the mail as junk mail. Finally I ended up communicating by Skype text. They all write very good English which is a bit embarrassing as my Mandarin is non existent. My kids are learning Mandarin at school though.
Payment was via Paypal which remains safer than using a credit card (for both parties) and far cheaper than an interbank transfer.
I hope this Instructable is useful. I have built many hundreds of prototype boards over the last twenty years but I think from now on I will be getting boards made professionally.