ELEC 332

Combining Multiple Boards

The T-Tech machine requires a border around the board being milled in order to support the presure foot. This means that for small boards, most of the board material will be wasted. You can save board material and time, by combining multiple small boards into a single larger board or "panel".

Building a Panel

1. Set up directory structure
These instructions assume that you have set up a directory structure as described in the PCB Layout Tutorial. A skeleton of this structure, along with some template files and the build_panel program is contained in the pcb.zip file. If you have not set up this structure previously, you should download and unpack this file before proceeding.

At this point you should have the following structure: 

pcb                     ; root directory of pcb related files
|-- board1              ; design files for board1
|   |-- TOP.art            ; artwork for top layer
|   |-- BOTTOM.art         ; artwork for bottom layer
|   `-- board1-1-2.drl     ; drill file
|-- board2              ; design files for board 2
|-- build_panel.exe     ; the program for combining multiple boards into a single panel
|-- frames              ; directories containing board layout template files
|   |-- frame1x2           ; frame for one double size module
|   `-- frame2x1           ; frame for two single size modules
|       `-- holes.drl         ; drill file for 2 x 1 frame
|-- panel.txt           ; control file for build_panel program
`-- panel1              ; directory where pcb mill files will go
The filenames for the artwork and drill files are from the Cadence Allegro PCB layout program. If you have used different layout software, your files may have different names.
2. Assemble artwork and drill files
The artwork and drill files for each board should be in a separate subdirectory of your pcb directory. In this example these directories are board1 and board2.
3. Create the control file
The actions required to merge the boards into a panel are defined in a control file. I.e. build_panel is a batch, rather than interactive program.
Define the directory where the output files will be placed
The merged artwork and drill files will be placed in a separate directory, consistent with the structure described above. The first line of the file defines that directory: 
output panel1
Specify the correction for hole/pad alignment
The Quick Circuit/HF in the basement has a flaw which causes the holes to be offset from the traces by 5 mils. If you are using this machine you should include the following line to correct this problem: 
hole_offset -5 0

The new T-Tech QCJ5 does not have this problem, so if you will be milling in this machine, set the offset to zero or omit this line.

Define each board to be placed
Each board is defined by giving the name of its directory, the software package with which it was created, and a list of the layers. Each layer is defined by giving its layer name and its file name. Here is the definition of board1: 
board board1 allegro15
layer top TOP.art
layer bottom BOTTOM.art
layer drill ncdrill1.tap
/board

The board definition begins with the word "board", followed by the name of the directory in which the files are located and the name of the software package which created them. Recognized software packages are "allegro15" for Allegro version 15 and "allegro16" for Cadence Allegro version 16. The board definition ends with the line "/board".

A layer definition begins with the word "layer", followed by the name of the layer and the name of the file which defines that layer. Recognized layer names are "top", "bottom", and "drill".

Here are the remaining board definitions in our example: 


board board2 allegro16
layer top TOP.art
layer bottom BOTTOM.art
layer drill CPU02a-1-2.drl
/board

board frames/frame2x1
layer drill holes.drl
/board

frame2x1 contains the mounting and separation holes for a panel consisting of two 1.5" x 1.5" ELEC 332 breadboard modules. If you are not building modules for this format, you should omit this board, or define a suitable frame for your own boards.

Define the location of the boards
Boards are placed on the panel with the "place" command. Its arguments are the directory name of the board being placed (which must have appeared in one of the board definitions), its location (x and y coordinates), and its orientation. The location represents the position of the origin of the board coordinate system in the coordinate system of the T-Tech machine. The orientation argument is currently ignored, but must be present. 
place board1 0 -750 0
place board2 1500 -750 0
place frames/frame2x1 0 0 0

This example assumes that the origin of the board coordinates is at the lower left corner of the board. The origin of the T-Tech coordinates is 200 mils to the right of the front tooling pin.

4. Run build_panel
build_panel is a command line program. To run it, open a command prompt window and change directory to your pcb directory. Type build_panel sample_panel.txt. If all goes will, it will do its job silently. If not, it will print error messages describing what it doesn't like.
5. Proceed to mill board
The directory panel1 should now contain three files: top.gbr, bottom.gbr, and holes.drl. These are the files which define the merged panel. At this point you are ready for the Process Layout Files step of the Basic PCB Milling instructions.