Introduction

When designing a test fixture using FixturFab, our preferred method for entering test point locations is to use a Test Point CSV file. This file contains a list of all of the test points that will be used within the fixture along with their locations. A public example can be found here.

CSV File Format

The CSV file needs to contain columns with the following headers:

  • Net
    • Contains the net name that is attached to the test point
  • Name
    • Reference designator given to the test point
  • X Coord
    • X-Coordinate of the test point (in mm)
  • Y Coord
    • Y-Coordinate of the test point (in mm)
  • Side
    • Layer that the test point is on (Top, Bottom, or Both)
      • Use Bottom if the test point is through-hole and can be probed from either side
  • Type
    • Test point type, surface mount (SMD), or Through-Hole

A template is available from this google sheet. Make a copy of this Google Sheet by selecting File > Make a copy, this will create a copy of the template that you can save to your own Google account.

If you prefer to not use Google Sheets, the sheet can be downloaded as a CSV file. Select the Test Point List sheet, and then download a CSV of the sheet by selecting File > Download > Comma-separated values (.CSV).

csv-dut.png

Identifying Test Points

Depending on the ECAD tool you are using, there are several different ways to identify and add your test points to the Test Point CSV file.

If you are using Altium, a Test Point CSV file can be generated. We have a blog post on our preferred method.

For Eagle or Kicad, you will need to open up the PCB design file, and then manually identify the coordinates for each test point that will be used in the fixture.

Select the test point, and then enter the information for it into the Test Point CSV file.

brd-tps.png

In this example, we will add test points for all six pads of this connector. The name of the test points will start with the reference designator (J3), and then be followed with an “-” and the pad number. For example, the first pad (SCL) would be named J3-1.

To determine the coordinates of the rest of the pads, we will need to add the pitch of the connector to the X coordinate of the first pad.

csv-tps.png

Tip: You can use formulas within the DUT Information template on Google Sheets to easily calculate the locations of multi-pin connectors.

Enter the information for all of the test point locations that you would like to use within the fixture.

Identifying Locating Features

To accurately locate the DUT within the test fixture, locating features need to be used. Our preferred method to locate a DUT is to use 3 or more mounting holes along with Spring Guide Pins. This will allow for the DUT to be supported and correctly located over the test probes.

Select the mounting hole and then enter the location data into the DUT Information sheet.

brd-guide-pins.png

The Net and Side columns can be left blank, and use a name that will help you identify which mounting hole it is (i.e GP-1). For the Type, select Locating Pin.

csv-guide-pins.png

If mounting holes are not available, place guide pins along the edges and cutouts of the DUT. Place the coordinates so that the edge of a 2mm or 3mm diameter guide pin lines up with the edge of the board.

Adding Pressure Pins

To press the DUT against the test probes within the fixture, pressure pins are used. These need to be located so that they push against the PCB, and not on top of any components.

The pressure pins that we use have a 3mm diameter tip. To find the best locations, we add a 3mm diameter circle to one of the mechanical layers of the PCB. Note: This layer is only used for identifying pressure pin locations, it is not included in the gerbers that are sent to the board fabricator.

The pressure pins should be distributed evenly across the PCB, for this example, we will place 4 pins near the 4 corners of the PCB.

To add the pressure pins to the DUT Information sheet, select the pin.

brd-pressure-pins.png

The Net and Side columns can be left blank, enter a Name to help you identify which pressure pin is which, and select Pressure Pin.

csv-pressure-pins.png

Exporting the CSV file

The Test Point CSV file now has all of the information needed to create a FixturFab project. Export it by selecting File > Download > Comma-separated values (.csv, current sheet). This file can then be uploaded directly to FixturFab or sent to us for an estimate.


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