VisualCAM supports two types of bare board test: bed of nails and flying probe. Tutorials for generating the necessary test files for each type of test are below.
Recommended reading on the basics of bare board testing:
"Bare Board Electrical Testing" by Philip J. Hallee, Everett Charles Technologies
"The Continued Evolution of Test Data Transfer Format IPC-D-356" by DuaneDelfosse, The Board Authority
Bed of nails testing is also referred to as "fixtured" or "clamshell" testing. Probes or pins, arrayed on a grid, are used to make contact with each point on a circuit to determine if the connection is good. To accomplish this, a netlist is used to determine where the probes must make contact with the board. Special plates are used to guide the probes to the desired points, so these plates must be defined and drilled. The following tutorial explains how to prepare your data, and create the necessary files for testing.
Using the Setup|Layers command or the Navigator, make sure that each layer is "tagged" with the correct layer type. This is required so that the system understands what each layer is.
When you create your test points, they will be added to a new layer. The layers should be named appropriately.
If you selected the Setup|Layers command, find an empty, unnamed layer in the Layer Setup dialog box. If you will be testing only the top side of your board, name the empty layer test_top. If you will be testing only the bottom side, name the empty layer test_bot. If you are testing both sides of your board, you will need to select two empty layers and name them test_top and test_bot, respectively. The other information for the layer should remain the default setting.
If you are working in the Navigator, right-click on the Layers heading, and select Add Layer from the shortcut menu. If you will be testing only the top side of your board, name the empty layer test_top. If you will be testing only the bottom side, name the empty layer test_bot. If you are testing both sides of your board, you will need to select the Add Layers command twice to create two empty layers. and name them test_top and test_bot, respectively.
Remove any extraneous data on your electrical layers that are outside the perimeter of the board, such as title blocks, targets, crop marks, etc.
Tip: We recommend that any documentation for the board be done on a separate Drawing layer. If you wish to keep the data, placing it on a drawing layer assures it will not interfere with any processing, such as netlist extraction.
If you have any drawn pads in your database, select one of the Tools|Convert|Drawn Pads commands to convert them to flashes.
Use the Analysis|DRC/MRC command to make sure your layers are properly aligned. If any layers are misaligned, you can use the Edit|Align Layers command to align them.
Use the Tools|Pad Removal|Stacked command to remove any redundant pads.
Select the Tools|Netlist|Generate command to extract a netlist from your data.
Select the Tools|Test Points|Setup command. Select the Bed Of Nails option, and indicate whether you are testing a single- or double-sided board.
If you are testing a single-sided board, indicate whether the tested (Output) layer is the Top or Bottom layer. The Target Layer is the layer that you wish to place your test point graphics on. Select the appropriate layer, which you created in Step 3.
If you are testing a double-sided board, select the appropriate Target Layer for each side of the board. test_top should be the top target layer, test_bot should be the bottom target layer.
Now you need to select the parameters for your fixture plates and probes. In the Grid Size box, select the spacing between grid points (this is a single-density grid).
Click the Probe Setup button. The Probe Setup Table contains a list of probes assigned to pads that are created using the D-codes given in the list. By default, the probe with code 1 is assigned to all pads. To change the assignment, click on the desired Probe Code and type the new number in the text box.
To change the Probe Code settings, click on the Probe Properties button. The Probe Properties dialog box appears. The probe diameter, length and maximum deflection angle (the largest angle a probe can employ while testing a point) appear below the table. To change any values, click on any item in the list and type the new value. When you are finished defining your probes, click OK. Click OK again in the Test Setup dialog box.
VisualCAM will use the Fixture Parameters when generating the fixture plate drill files for this design. If a tool of the exact size required is not found, the closest larger size tool will be used.
Select the Tools|Test Points|Generate command. Now you are specifying what types of pads are tested. Ends Only specifies that only the ends of traces are to be tested. All specifies that all pads are to be tested. Select Ignore Isolated to overlook isolated pads. Click OK when you have completed your selections.
The system scans your data and creates the test points. The graphics representing your test points appear on the test_top and/or test_bot layers.
You can add additional test points, if necessary, using the Tools|Test Points|Add command. To delete test points, either select the Edit|Undo command immediately after generating test points, or use the Edit|Delete command and set the selection filter to delete only flashes on the test_top or test_bot layer where the test points are placed.
Automatic test point staggering is used to provide additional spacing between test probes, to insure there is no probe-to-probe contact. It does this by offsetting the location of the test point from the center of the corresponding pad. Staggering is necessary if you have a large number of probes in a small area, such as a fine-pitch SMT component. Select the Tools|Test Points|Stagger command if you wish to stagger any test points.
Select the Tools|Test Points|Test Fixture|Snap To Grid command to "snap" the test points to the fixture plate grid. This tells VisualCAM where to create the drill holes in the fixture plates.
The following graphic shows an example of what should appear in the workspace, at this point (the colors of the items may differ from your workspace). The blue and gray flashes on the test_top and test_bot layers represent test points. The red and orange flashes show where the probes initially enter the fixture guide plates, and the line shows the path of the probe from the plate to the test point.
Select the Tools|Test Points|Test Fixture|Save Files command. This is where you specify all the parameters defining the probes and fixture plate requirements. You can define up to seven fixture plates. The Grid plate is the plate closest to the fixture machine, and the Board plate is the plate closest to the PCB. The Guide plates are aids for guiding the probes to the correct location on the board.
Tip: If you are creating a double-sided text fixture, you must specify the file information for both sides of the board. You are first presented with the information for the top side. To specify the information for the bottom side, click the Bottom Side button at the bottom of the dialog box. The button is a toggle, so you can switch from top to bottom side at will.
Select (check) the number of guides you require, and change the default names, if you wish.
Dist is the distance of each plate to the board. Thick is the thickness of the fixture plate. You can change either of these values.
Enter the desired netlist filename. By default, the netlist file is saved in the native VisualCAM .nl format. To save the netlist as an IPC-D-356A file (.net), select the IPC-D-356A option.
The Grid/Board Map File is an ASCII report file that shows the probe assignment for each location, the coordinates of the test point, and corresponding probe grid location. Specify a name for the .txt file.
Click the NC Format button if you wish to change the format used for the output test point drill file.
If you wish to change any of the tool information in the NC Tool table, click the Tool Setup button.
When you are finished defining the fixture information, click OK to save the files.
Flying probe is also known as "moving probe" and "X:Y prober". Unlike bed of nails testers, which test multiple nets at once, flying probe test systems use two or more points which rapidly move around the board area, testing each net individually. Due to the nature of the testing, it is not subjected to limitations due to test point density. No staggering or guide plates are required to aid the test machine.
Import your data or open a previously-created VisualCAM .vcam file.
Using the Setup|Layers command or the Navigator, make sure that each layer is "tagged" with the correct layer type. This is required so that the system understands what each layer is.
When you create your test points, they will be added to a new layer. The layers should be named appropriately.
If you selected the Setup|Layers command, find an empty, unnamed layer in the Layer Setup dialog box. If you will be testing only the top side of your board, name the empty layer test_top. If you will be testing only the bottom side, name the empty layer test_bot. If you are testing both sides of your board, you will need to select two empty layers and name them test_top and test_bot, respectively. The other information for the layer should remain the default setting.
If you are working in the Navigator, right-click on the Layers heading, and select Add Layer from the shortcut menu. If you will be testing only the top side of your board, name the empty layer test_top. If you will be testing only the bottom side, name the empty layer test_bot. If you are testing both sides of your board, you will need to select the Add Layers command twice to create two empty layers. and name them test_top and test_bot, respectively.
Remove any extraneous data on your electrical layers that are outside the perimeter of the board, such as title blocks, targets, crop marks, etc.
Tip: We recommend that any documentation for the board be done on a separate drawing layer. If you wish to keep the data, placing it on a drawing layer assures it will not interfere with any processing, such as netlist extraction.
If you have any drawn pads in your database, select one of the Tools|Convert|Drawn Pads commands to convert them to flashes.
Use the Analysis|DRC/MRC command to make sure your layers are properly aligned. If any layers are misaligned, you can use the Edit|Align Layers command to align them.
Use the Tools|Pad Removal|Stacked command to remove any redundant pads.
Select the Tools|Netlist|Generate command to extract a netlist from your data.
Select the Tools|Test Points|Setup command. Select the Flying Probe option, and indicate whether you are testing a single- or double-sided board.
If you are testing a single-sided board, indicate whether the tested (Output) layer is the Top or Bottom layer. The Target Layer is the layer that you wish to place your test point graphics on. Select the appropriate layer, which you created in Step 3.
If you are testing a double-sided board, select the appropriate Target Layer for each side of the board. test_top should be the top target layer, test_bot should be the bottom target layer.
Click OK to close the Test Setup dialog box.
Select the Tools|Test Points|Generate command. Now you are specifying what types of pads are tested. Ends Only specifies that only the ends of traces are to be tested. All specifies that all pads are to be tested. Select Ignore Isolated to overlook isolated pads. Click OK when you have completed your selections.
The system scans your data and creates the test points. The graphics (flashes) representing your test points appear on the test_top and/or test_bot layers.
You can add additional test points, if necessary, using the Tools|Test Points|Add command. To delete test points, either select the Edit|Undo command immediately after generating test points, or use the Edit|Delete command and set the selection filter to delete only flashes on the test_top or test_bot layer where the test points are placed.
Select the Tools|Test Points|Flying Probe|IPC-D-356A command to save your test file.
Specify the name of the .net file you are exporting. To search for a file or directory, click the Browse button.
Specify the Net To Net Adjacency Distance. Any nets within this distance to a net being tested will be tested for shorts.
Click Save to save the file.