Design for Testability

The testability of the printed circuit board (PCB) is not always taken under consideration during the design process. The consequence could be higher costs to the test or a degraded test. Below please find recommendations which will make a printed circuit board (PCB) suitable for test in Torolex test fixtures.

Test points:

• Preferred test points. Test points are prioritiesed as: 1. Test pads, 2. Leaded component pins. Test of SMD pads and VIA's should be avoided.
• Single sided test. All test points must be placed on the 'solder' side of the PCB.
• Close test pads. For use of the most common the pads the center to center distance must be minimum 2,54mm (0,100").
• Pad size. The preferred size of test pads is 1,2mm  or bigger.
• Short pins. The length of pins from leaded components should be less than 3mm after soldering.
• Test guide distance. The distance from the center of a test pad to the center of the PCB fixing hole must be minimum 4mm.
• High components. Test points should have a minimum distance of 3 mm to high components (>5mm) on the solder side.
• Connectors. Connector pins should be available on the test side of the PCB. If not add test pads.
• Hidden Pads. Required signals may be hidden behind piggyback PCB’s, displays or keyboards. Add test pads.

The most common and recommended test probe center to center distance is 2,54mm  (100mil). But we also support fine pitch test probes with 1,91mm (075mil) and 1,27mm (050mil) distances.

PCB Fixing Holes:

• Opposite corners. Holes used to fix the PCB during test should be placed in opposite diagonal corners of the PCB to maximize the accuracy of the PCB position. 
• Min 2 holes. A minimum of 2 PCB fixing holes should be available.
• Symmetric holes. Avoid symmetric position of  the holes to limit the possibility of mounting the PCB 180 deg. turned.

If the PCB is already manufactured and you have recognized a problem then don't hesitate to contact us. A discussion may help you to find a suitable solution for your test problem.