Importance of PCB test points for circuit boards

The circuit boards we design also need to pass some tests. In their case, the tests will determine their manufacturing quality. In order to perform this test, it is necessary to prepare the board with specific elements that can be accessed by the test probes.wafer tester These elements are called test points and it is very important that they are included in the PCB design. Let's take a few minutes here to discuss PCB test points and why it is so important to the success of the completed circuit board.

There are two main types of test points used on printed circuit boards. The first are points that are easily accessible to technicians using handheld test equipment. To address this, a lug is usually soldered to these points to clamp the test leads. These test points will be labeled with a reference mark, usually a screen name in screen printing for easy reference, such as " GND".

Another type of test point is used primarily for automated test equipment. Automated test points on circuit boards are through-hole pins, via holes, or small metal pads designed to accommodate the probes of an automated test system. There are three main types of test systems that will use these test points on the board:

Bare Board Test: This is a test run after the board has been manufactured to ensure that all networks on the board have electrical connectivity.

In-circuit testing: ICT is run after the board has been assembled. the board sits on ICT fixtures that contain probes for each individual network. These fixtures usually test the bottom of the board, but they can also test the top or sides of the board together if required.

Flying probe: As with ICT, this test is performed by accessing the test points on each network on the board after assembly is complete.wafer probe testing However, the difference is that flying probe equipment uses two to six probes that can be moved to each test point, rather than fixed probes in a fixture as in ICT.

These are the different test points that will be included in the PCB design and what they are used for. Next, we will look at why this test is so important for circuit board manufacturing.

Why Test Points are Important for PCB Manufacturing

Automated testing is vital to validate the manufacturing of printed circuit boards. Bare board testing will check that the manufactured board has good connectivity, while ICT and flying probe testing will verify board assembly and solder connections. This is how ICT and flying probe testing is accomplished:

In-Circuit Testing (ICT)

ICT is a system that uses test fixtures prepared specifically for a particular board design and accompanying software that will run on the test system. The fixtures and software are created using test point locations and other design data generated from a CAD database, and a probe will be used for each network in the design.The primary purpose of ICT is to verify board assembly by testing that each network has a good connection to its associated part pins, but it can also be used to test the functionality of the board.

ICT test fixtures and software development are costly and time consuming. Test fixtures are complex, containing thousands of probes, and changing fixtures for board revisions is expensive. However, once developed, in-circuit testing will test large numbers of boards very quickly. For volume 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 assembled boards, but this is quite different from ICT.vibration isolation table Instead of test fixtures, only two to six probes can fly around to access every test point on the board. A flying probe system can be installed quickly and inexpensively without the need to build expensive test fixtures. In addition, any board changes that need to be made to the test system can be easily reprogrammed.

The disadvantage of flying probes is that they are very slow. whereas ICT can test almost all points on a board instantaneously, flying probe systems must maneuver their probes 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 production runs, testing with flying probes can be very beneficial.

Most PCB design systems will provide specific tools or features for adding test points to the design. Typically, before assigning test points, these tools will need to first set up their parameters as shown above. These parameters will cover a variety of details such as the distances allowed for test points from each other and the rest of the design of the test rules. After setting up the parameters, designers can add test points automatically or manually during the iteration process.

Test points are usually assigned to any available through-hole pins first, and then to the through-holes. If there are no available through-holes, these tools will enable the designer to add new through-holes to the trace. There will also be a number of options available when assigning test points, such as adding specific reference marks or changing the shape of the via pads from round to square.