Some Information About Set Test Points on PCB

With the development of technology, the size of the circuit board is getting smaller and smaller. It is already a bit difficult to install so many electronic parts on a small circuit board. Therefore, the problem of the test point occupying the circuit board space is a tug-of-war between the design side and the manufacturing side. The appearance of the test point is usually round, because the probe is also round, which is easier to produce, and it is easier to bring adjacent probes closer, so as to increase the needle density of the needle bed.

1. The use of needle beds for circuit testing has some inherent limitations on the mechanism. For example, the minimum diameter of the probe has a certain limit, and the needle with too small diameter is easy to break and damage.

2. The distance between the needles is also limited, because each needle must come out of a hole, and the back end of each needle must be welded with a flat cable. If the adjacent holes are too small, it will occur contact short-circuit problem between needles, and interference of the flat cable.

3. Needles cannot be implanted next to some tall parts. If the probe is too close to the high part, there is a risk of collision with the tall part and cause damage. In addition, because of the high part, it is usually necessary to make a hole in the test fixture needle bed base to avoid it, which indirectly makes it impossible to implant the needle. Test points for all parts that are increasingly difficult to accommodate on PCB.

4. As the board is getting smaller and smaller, the number of test points has been repeatedly discussed. Now there are some methods to reduce test points, such as Net test, Test Jet, Boundary Scan, JTAG, etc.. there are also other tests method which replace the original bed of needle tests, such as AOI and X-Ray, but it seems that each test cannot replace ICT 100%.

Regarding the ability of ICT needle implantation, you should ask the matching fixture manufacturer about the minimum diameter of the test point and the minimum distance between adjacent test points. Usually there will be a desired minimum value and a minimum value that the ability can achieve. But there are large-scale manufacturers will require that the distance between two the minimum test point cannot exceed a few points, otherwise the jig will be easily damaged.