PCB Technical - PCB test points and their importance to circuit board manufacturing

What are the different types of test points used on printed circuit boards?Why are pcb test points important for successful circuit board manufacturing?

Just mention the word "test" and most people will feel their heart beating faster.From the first day of elementary school, there seems to be a fear of exams. However, as we all know, testing is a very important part of life.You don't want to fly in an airplane with a pilot who has not passed the flight check,and the idea of a surgeon brandishing a scalpel without passing his basic anatomy course scares everyone.

The circuit board we designed also needs to pass some tests. In their case, testing will determine their manufacturing quality. In order to perform this test, the specific elements that the test probe can access must be prepared for the circuit board. These elements are called test points, and they are very important to include in the PCB design. Let us spend a few minutes here to discuss the PCB test points and why it is so important for the success of the completed circuit board.

Different types of PCB test points

There are two main types of test points used on printed circuit boards. The first is a point that technicians can easily access using handheld test equipment. To solve this problem, a terminal is usually welded to these points to clamp the test leads. These test points will be marked with a reference mark, usually with a screen name in the screen printing for easy reference, such as "GND".

Another type of test point is mainly used for automated test equipment. The automatic test points on the circuit board are through-hole pins, vias or small metal pads, which are designed to accommodate the probes of the automatic test system. There are three main test systems that will use these pcb test points on the board:

.Bare board test: This is a test performed after the circuit board is manufactured to ensure that all networks on the board have electrical connectivity.

.On-line test: run ICT after assembling the circuit board. The board is located on the ICT fixture, which contains probes for each individual network. These fixtures usually test the bottom of the circuit board, but if necessary, they can also test the top or both sides of the circuit board together.

.Flying probe: Like ICT, the test is performed on each network on the circuit board by visiting test points after assembly. However, the difference is that the flying probe device uses 2 to 6 probes that can be moved to each test point, instead of using fixed probes in a fixed device like ICT.

These are the different test points that will be included in the PCB design and their purpose. Next, we will understand why this test is so important for circuit board manufacturing.

Why test points are important for PCB manufacturing

Automated testing is essential to verify the manufacture of printed circuit boards. The bare board test will check whether the man-made board has good connectivity, while the ICT and flying probe test will verify the board assembly and solder connection.

Practical application of ICT and flying probe test:

Online Test (ICT)

ICT is a system that uses test fixtures specially prepared for a specific circuit board design and accompanying software that will run on the test system. Use test point locations and other design data generated by the CAD database to create fixtures and software, and a probe will be used for each network in the design. The main purpose of ICT is to verify the assembly of the circuit board by testing the good connection of each network and its related component pins, but it can also be used to test the function of the circuit board.

ICT test equipment and software development are costly and time-consuming. The test fixture is very complex, which contains thousands of probes, and the cost of changing the fixture for circuit board revision is also very expensive. However, once the development is complete, online testing will test a large number of circuit boards very quickly. For mass production, the advantages of speed and functional testing quickly offset the development time and cost of ICT.

Flying probe test

The system is also designed to verify the integrity of the assembled circuit board, but this is completely different from ICT. Instead of a test fixture, only two to six probes can fly around to visit each test point on the board. The flying probe system can be installed quickly and inexpensively without constructing expensive test fixtures. In addition, any board changes that require changes to the test system can be easily reprogrammed.

The disadvantage of flying probes is that they are very slow. ICT can almost instantly test all points on the board, while the flying probe system must maneuver its probe to each individual test point. On large boards, this can take a long time and eliminates the ability to perform functional tests. However, for prototypes or small batch production, using flying probes for pcb test points can be very beneficial.