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Knowledge For PCB Introduction to PCB test processes

Introduction to PCB test processes

August 31, 2022     Knowledge For PCB

electrical path test

Introduction to PCB test processes

Testing technology is an important tool to ensure the implementation of the process. According to the development of electro-assembly technology from pin-in-place technology to surface packaging technology (bare chip direct mounting technology and fine pitch technology), multi-chip module (MCM) technology or multi-chip packaging technology, it has become more difficult to inspect the circuit patterns of multilayer printed circuit boards. For this reason, both domestic and international are developing and using high-precision and highly stable inspection equipment. Currently there are two types of inspection equipment i.e. contact and non-contact.

1, non-contact inspection technology

Detection technology is a heavy means of providing physical and chemical properties data of printed circuit boards. With the change in the accuracy and density of printed graphics, the past quite a long time using manual visual methods have not adapted to the needs of the rapid development of high-tech, detection technology and equipment has been developed rapidly, from the use of functional gradually replaced the manual visual inspection to determine product quality, it is from the appearance of the circuit graphics to the inner circuit graphics detection, thus pushing the simple detection of inter-process quality monitoring and Defects repair combined with the direction of development. Its main features are: the use and application of computer hardware and software technology, high-speed image processing and pattern recognition technology, high-speed processing hardware, automatic control, precision machinery and optical technology, is the product of a comprehensive variety of high technology. No contact, no damage, no damage to the detection parts, can detect the contact detection can not be. Among the equipment are the following.

Bare board appearance inspection technology and equipment

a, AOI (Auto Optical Inspection).

It is an automatic optical identification system. Based on production efficiency and inspection accuracy considerations, the use of optical recognition instruments to replace manual visual inspection (Visual Inspection) is already a very basic process. The principle of AOI is to store the standard image file in the equipment, use the image file and the object to conduct optical comparison, and automatically determine whether the error of the object exceeds the standard, if the error is too large, then pick out to determine whether the abnormality is scrapped or repaired. As the lines on today's circuit boards are becoming more and more delicate, and have long exceeded the limits of what can be found by the human eye, most of the PCB AOI equipment is used to check and compare the line layers to see if there is damage such as too much/too little etching or collision.
Mainly using the design specification inspection method to test two-dimensional digital graphics, with the emergence of surface mount technology with and three-dimensional molded printed circuit boards, the design specification inspection method will have a completely different connotation. It can not only test the width of the wire and line spacing, but also the height of the wire. So the existence of three-dimensional layout, necessarily more advanced sensors and imaging technology. Non-contact AOI testing technology is a combination of X-ray, infrared technology, and other detection technologies in one product.

b, X-ray inner layer fluoroscopy detection technology

The early use of X-ray because of the focal length of 300μm degree, its detection accuracy can only reach 0.05mm. the current focal length has reached the micron level, has been able to enter the accuracy of 10 micron measurement. With the image processing and can be used for multi-layer printed circuit board of the inner circuit graphics for high resolution perspective and detection.

2、Contact inspection technology and equipment

Printed circuit board inspection methods, mainly using online testers also known as static function test. Currently there are a variety of models, advanced equipment can quickly to the manufacturing process errors resulting in quality defects (including open circuit, short circuit). There are general-purpose through-circuit tester, special through-circuit tester and flying probe type of mobile through-circuit tester. The latter type is suitable for electrical performance testing of small batch high density, high precision double-sided and multi-layer printed circuit boards.

a,Electrical path test.

One hundred percent electrical path test is already a specification that almost all customers will require for inspection. But even if the customer does not require it, PCB manufacturers will do electrical testing to ensure that all shipped products do not have any pathway defects. Electrical path testing can be divided into the following ways.

b, Flying Probe.

The principle of the flying probe test is simply to place the PCB board on the machine and fix it. 2 to 4 probes of the test machine move back and forth constantly to touch the solder pads and pilot holes to detect whether each pathway is the same as the original design or there is a broken circuit/short circuit abnormality. Due to the rapid movement of the probes back and forth, so it is called flying probe test. This is a very basic electrical test inspection method, the advantage is that no special fixtures need to be made, just clip the board up and down or left and right in the equipment can be fixed, very suitable for small quantities or samples; the disadvantage is that the test takes longer, the more points to be tested will be longer, not suitable for testing mass production boards.

c,Dedicated type (Dedicated).

For traditional Dedicated type, it is necessary to commission a fixture supplier to make a test fixture that fits the product, and the fixture is completed with the test pins inserted for each test point and the path leads connected. After the test is completed, the fixture cannot be separated and can only be stored as a whole.

d, Universal on Grid test.

In the case of Universal on Grid, the test fixture is made by the same fixture supplier, and the fixture is only drilled for the test points without connecting any wires. Before the test, the PCB manufacturer only needs to insert pins in each hole and set the fixture on the upper and lower pins of the electrical test machine. During the test, the upper and lower pins of the machine only need to touch the test points through the test pins, and then it can correctly detect whether the PCB path is correct. And the universal fixture can be disassembled after the use of the test pins and the body, easy to store.

 

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