The necessity of testing points on PCB boards!

Some people may ask, "PCB design plan: why do I have to have test points on a PCB?" It's very likely that I'm still a bit confused. The purpose of setting most test points is to better test whether the components on the circuit board meet the specifications, models, and solderability. For example, to check if there is a problem with a resistor on a circuit board, an effective method is to measure both sides with a multimeter to determine. The details are as follows:

However, in large-scale manufacturing factories, there is no way for you to gradually measure the appropriateness of every resistor, capacitor, inductor, and even the power circuit of an IC on every piece of wood using an electricity meter. Therefore, there is the so-called ICT (In Circuit Test) automation technology testing machine equipment, It uses multiple probes (commonly referred to as "Bed Of Nails" fixtures) to simultaneously touch all the parts on the board that must be measured. Then, through program control, the coding sequence is dominant and auxiliary methods are used to sequentially measure the characteristics of this electronic part. Usually, testing all parts of the board can be carried out in about 1-2 minutes, depending on the number of parts on the circuit board, The more parts, the longer the time.

However, if this type of probe directly contacts the electronic parts or their solder legs behind the wooden board, it is highly likely to crush some electronic parts, which is not worth the loss. Therefore, the intelligent technical engineer discovered the "test point" and added a pair of small circular points on both sides of the part, without a solder mask on the top, which can allow the testing probe to touch these small points, Without direct contact with these measured electronic parts.

In the early days of traditional software (DIP) on circuit boards, it was true that the solder holes of parts were used as test points. Due to the robust solder holes of traditional parts, they were not afraid of punctures, but there were often misjudgments of poor probe contact. This was due to the fact that ordinary electronic parts were tinned through wave soldering or SMT, On the surface of its solder wire, a layer of residual plastic film with solder paste and flux is usually generated. The characteristic impedance of this layer of film is very high, which often leads to poor contact of the probe. Therefore, at that time, it is often seen that testing operators on production lines often used gas spray guns to blow desperately, or used alcohol to wipe the area that must be tested.

In fact, poor contact of the probe can also occur at the testing points of the wave soldering machine. After the popularity of SMT, significant improvements were made in the situation of misjudgment in testing, and the use of test points was greatly burdened. Due to the sensitive nature of SMT parts, they were unable to bear the immediate contact stress of the test probe. By using test points, the probe could not directly contact the parts and welding holes, which not only maintained the parts from being injured, but also indirectly greatly improved the stability of testing. As the number of misjudgments decreased.

But with the evolution of science and technology, the specifications of circuit boards have become smaller and smaller, and the small ground circuit boards have to be squeezed with light