All you need to know about PCB test

PCB procurement is not a simple matter and there are many factors to consider including quality, price, lead time, etc. Based on our experience, we recommend that you produce prototypes before making bulk orders. This way, even if there are problems, the designers will be able to make adjustments according to the problems that arise in production. In addition, each PCB is checked for its specific design and performance to maximize the final yield, help us save on procurement costs, and prevent problems during the bulk order production phase of the PCB. This is also to ensure that the performance, functionality, safety, and reliability of the PCBs meet the requirements and that the project proceeds smoothly as expected. In this article, I will introduce you to 8 PCB testing methods to help you understand how to test the quality of PCB boards.

1.?AOI(Automatic Optic Inspection) Test

??#AOI is an automated visual inspection based on optical principles that use integrated image analysis, and computer and automatic control technologies to detect the presence of surface defects on PCBs.

Generally speaking, is in the PCB to complete the figure of electricity, that is, electro-copper, electro-tin, de-filming, etching, and de-tinning these links can begin to AOI optical inspection of the board.

The technician will be tested PCB board onto the AOI inspection panel, then the AOI instrument will use a high-resolution two-dimensional camera or three-dimensional camera to start scanning the PCB, the scanned circuit board pictures, and detailed schematic diagrams for comparison, to see if there are inconsistencies is whether there are line width violations, spacing violations, open circuits, short circuits, and broken places. If there are inconsistencies, the AOI machine will mark them out for the convenience of technicians' checks. Compared to manual visual inspection, AOI has the advantage of being able to perform all inspections in a completely automatic, accurate, and fast manner, stopping production at an early stage of PCB production to make appropriate adjustments and correct defects. Of course, AOI testing also has disadvantages, it is very time-consuming to set up and program the template matching, each time the setting changes need to be completed again, and is not suitable for prototyping that requires modification.

2.?Flying Probe Test

??#Flyingprobetesting is an electrical test solution and an in-line test system.

First, the technician fixes the board with a simple fixture, then operates the flying probe tester to execute the on-board memory module, then the ECM compiles coordinates to match the board which means the software-controlled program corresponds the probes on the X-Y grid to the test nodes. Under the control of the software, multiple probes and test nodes that is pins, pads, and through-holes are contacted one by one to test for the presence of open, short, and broken circuits and marked in the program.

Compared to ICT, flying probe testing does not require custom equipment, that is, test stands, and only requires simple programming changes to adapt to new boards, which can reduce costs. This is usually suitable for prototype testing as well as small and medium-sized production. However, flying probe testing is slower, nearly 15 times slower than ICT circuit testing. Flying probe testing is also not compatible with complex circuits and cannot assess certain defects on complex PCBs such as excessive and insufficient solder.

3.?ICT(In Circuit Test)

??#ICT (In Circuit Test) testing, also called pin bed testing, is a highly accurate automated test.

This is done mainly by establishing a connection through a fixed probe that matches the PCB design with a test point contact on the PCB board to detect the presence of short circuits, open circuits, broken circuits, and component soldering faults.

Because it is controlled by a computer program with pre-designed access points on the board, ICT testing only takes about 3 to 5 seconds to complete defect detection in a fast, high-tempo manner, generating easy-to-interpret test reports that speed up the production process and reduce the cost of production time. This type of testing is typically used for high-volume production orders, the final stage of a mature product that requires no changes. Of course, ICT has its drawbacks: its test fixtures are fixed and cannot be changed, it is expensive, and it does not allow access to certain nodes in complex circuits. Therefore, we recommend that you first test prototype designs or small orders with flying probe testing to minimize the cost before mass production.

4.?Burn-in Test

??#Burnintesting is a more intense test of PCBs sometimes called accelerated life testing (a subset of HALT/HASS) to detect the early failure of PCBs and determine the load capacity of the PCB.

Power supply, military, and medical applications such as PCB safety requirements of high areas, are required to ensure the safety of burn-in testing to avoid safety hazards when the product reaches the end consumer.

Burn-in test is used in simulating extreme or prolonged operating conditions of the board to reveal the PCB in actual use may fail in the problem. These extreme operating conditions typically include changes in temperature (257°F or 125°C), operating frequency, voltage, current, or other operating conditions associated with the DUT. Burn-in tests last from 2 to 7 days or 48 to 168 hours, and the results provide designers with accurate information to understand the cause of failures and optimize the design and manufacturing process. However, Burn-in tests are conducted under extreme or prolonged operating conditions, exceeding the stress rating of the board, which may cause damage to the PCB components and thus shorten the life of the product. Therefore, we recommend that you find few or no defects during the PCB burn-in test, you can reduce the test limits in a shorter period of time to avoid excessive stress on the PCB.

5.?AXI(Automatic X-ray Inspection) Test

??#AXItest is really more of an inspection tool for most #ECMs (electronic contract manufacturers) to check for internal defects in wafers.

AXI creates 2D or 3D images of hidden solder joints and uses X-ray rays to examine solder joint voids, circuit connections, and solder under a ball grid array (#BGA) or quad flat lead (#QFN) package.

This test method can detect areas that cannot be detected during AOI testing usually detecting hidden solder joints between the component itself and the PCB surface, helping engineers identify and locate defects for process adjustments to eliminate the source of the problem. But AXI requires experienced technicians to operate and is a long and expensive process, usually applied to complex circuit boards with chip components and mass production.

6.?FCT(Functional Circuit Test)

In PCB assembly, ??#FCT (Functional Circuit Test) is a test tool that is divided into two parts, one is the main part and the other is the test fixture part. The main part includes a computer system and a signal sampling system.

The technician will place the PCB in the test rack, test probe points or edge connectors connected to the PCB, and then FCT tester by simulating the PCB in different operating conditions of the operating environment to obtain various parameters of the PCB to detect whether the PCB board meets the design requirements. The test fixture part has a fixed size, according to the different target test boards to do positioning holes. FCT function test items mainly include voltage, current, power, power factor, frequency, duty cycle, brightness and color, character recognition, voice recognition, temperature measurement, pressure measurement, motion control, FLASH and EEPROM burn-in, etc.

FCT testing is mainly applied to the middle and end of the PCB production line (from 50% to 100% of the products shipped), all done automatically by computer, with guaranteed efficiency and pass rate. This type of testing is well suited for use with other testing methods such as ICT testing and flying probe testing. However, the defect detection rate of FCT depends on the checks covered by the test plan, for example, under certain stress conditions, boards that have passed the functional test can still fail.

7.?Boundary Scan Test

??#Boundaryscantesting is a technique for inspecting ICs (integrated circuits) and interconnects on PCBs, also called #JATG, following the test architecture and procedures defined under the IEEE1149.1 standard.

Boundary-scan testing looks at the traces on the #PCB and is able to evaluate the board without reaching all the nodes of the PCB. In this test, the cells are placed in the leads from the silicon to the external pins to test the functionality of the board. Boundary-scan testing allows testing of complex and high-density ICs and boards, relying on a four-wire hardware interface to send and receive specific test signals to and from the IC and board under test for comprehensive testing, identifying possible faults in the PCB's pads, pins, and soldered BGA connections.

Compared to AXI testing, boundary-scan testing does not require expensive test equipment, so it is less expensive, more efficient, and also minimizes physical damage to pins and boards.

8.?Manual Visual Test

??#Visualizationtesting is a manual testing method and is the simplest form of PCB testing.

Quality control personnel visually inspect the surface of the board using a magnifying glass or calibrated microscope and then compare it to the design file for visible defects such as poor soldering, through holes, liner plating, board thickness, surface roughness, and warpage to ensure that the PCBs produced to meet customer requirements and relevant quality acceptance standards.

Visualization testing does not require test fixtures and complex setups and is easy and inexpensive to operate. It is able to troubleshoot faults that electrical testing cannot and identify most major solder defects, making it the most cost-effective testing method for prototypes and small-volume orders. Because it is a manual visual inspection, this also means that an experienced operator is required and visual inspection is only able to check visible solder joints, with a high probability of errors and missed defects.

Conclusion

According to different PCB types, we can set the corresponding quality acceptance criteria. Choose a different test method. No matter which test method is used, PCB testing is an essential step in the design process and can help you save a lot of time? and money??.

Don't know how to get started? I can help, welcome email?? [email protected] Or message?? me on WhatsApp/Telegram/Skype/WeChat:+8618026940954 to get a quote. For more information on PCB testing and other PCB industry knowledge, please check out the other articles on my homepage.