PCB testability design process requirements

- Sep 09, 2019-

The technical aspects of PCB manufacturing mainly consider the factors that affect the detection reliability, such as the positioning accuracy of ICT automatic test, substrate size, and probe type.

  1. Precise positioning hole. In order to ensure accurate positioning during ICT automatic testing, accurate positioning holes should be set on the substrate during PCB design. The positioning hole error should be within 0.05mm, at least two positioning holes should be set, and the farther the distance is, the better. Non-metallized positioning holes are used to prevent the solder plating in the holes from affecting the positioning accuracy. If it is a panel, the positioning holes are set on the main board and each of the separate substrates.


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2. The diameter of the test point is not less than 0.4mm, and the spacing between adjacent test points is preferably above 2.54mm, not less than 1.27mm.

3. The test surface can not be placed with a height of over 6.4mm, otherwise it will cause poor contact of the test fixture probe to the test point.

 

4. It is best to place the test point outside the component 1.0mm, to avoid damage caused by the impact of the probe and components. The positioning hole is not more than 3.2mm around the ring, and  components or test points are not allowed around.

5. Test points should not be placed within 4mm of the PCB clamping edge. This 4mm space is used to clamp the PCB, which is the same as the PCB clamping edge in SMT printing and placement equipment.


6. All probe points are preferably tinned or metal conductors that are soft, easy to penetrate, and not easily oxidized to ensure reliable contact.

7. Test points should not be covered by solder resist or text ink, otherwise the test point contact area will be reduced and the test reliability will be decreased.


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