Test Hole and Test Disc Design - Testable Design DFT (Part 2)
Second, the testability requirements of electrical potential
In order to ensure the testability of electrical performance, the test point design mainly has the following requirements.
1. Several test points can be set on the PCB. These test points can be holes or pads.
2. The requirements for the test hole setting are the same as those for the reflow soldering via.
3. The test pad surface has the same surface finish as the surface mount pad.
4. It is required to pass the SMC/SMD test point of the component surface (main surface) through the via hole to the soldering surface as much as possible. The diameter of the via hole should be greater than Im. This can be done by using the single-sided needle smell on-line test, and avoiding the needle bed test on both sides. , thereby reducing the cost of online testing.
5. Each electrical node must have a test point. Each IC must have a power and ground test. Point, the test pilot is as close as possible to this C device, preferably within the distance of IC2.54mm.
6. When setting test points on the wires of the circuit, the width can be enlarged to 40 mils.
7. Balance the test points on the printed board. If the probe is concentrated in a certain area, the higher pressure will deform the board or needle bed to be tested, and in severe cases, some probes will not touch the test point.
8. The power supply line on the circuit board should be set to test breakpoints in a sub-area, so that when the power supply decoupling capacitor or other components on the circuit board are short-circuited to the power supply, the fault point can be found more quickly and accurately. When designing a breakpoint, consideration should be given to restoring the power carrying capacity after the test breakpoint.
9. The probe test supports the via and the test point. When using the online test, the probe test support via and the test point are connected to the pad, which can be taken from anywhere in the wiring, but the following points should be noted:
1 Pay attention to the minimum spacing of probes of different diameters for automatic online testing (ATE).
2 vias cannot be selected on the extension of the pad.
3 test points can not be selected on the solder joints of the components. This test may cause the solder joints to be squeezed under the pressure of the probe.
Think of the location so that the solder joint is masked: in addition, it is possible to have the probe act directly on the end or pin of the component.
Causes damage to components.
4 probe test disc diameter is generally not less than 0.9mm.
5 test the minimum gap of the disk country, equal to 80% of the height of the adjacent components, the minimum gap is 0.6mm.
6 On the side of the PCB with the probe, the height of the part does not exceed 5.7mm. If it exceeds 5.7m, the test tooling must give way, avoiding
To open the component, the test pad must be 5 mm away from the high component.
7 Gold fingers are not used as test points to avoid damage.