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1. A.O.I. (automatic optical inspection)  
     AOI is the full name of automatic optical inspection, which is based on the optical principle to detect the common defects in the welding production. AOI is a new emerging testing technology, but it develops rapidly. Many manufacturers have introduced AOI testing equipment. When automatic detection, the machine automatically scans PCB through camera, collects images, compares the tested solder joints with the qualified parameters in the database, checks the defects on PCB through image processing, and displays / marks the defects through display or automatic mark for repair by maintenance personnel.
Using high-speed and high-precision visual processing technology to automatically detect various mounting errors and welding defects on PCB. PCB board can range from thin high density board to low density large size board, and can provide online detection scheme to improve production efficiency and welding quality. By using AOI as a tool to reduce defects, we can find and eliminate errors in the early stage of assembly process to achieve good process control. Early detection of defects will prevent the defective board from being sent to the subsequent assembly stage, and AOI will reduce the cost of repair and avoid scrapping the irreparable board.

Error types detected
After tin coating, before mounting: bridging, shifting, no tin, insufficient tin
After mounting and before reflow welding: displacement, missing material, polarity, skewness, foot bending and wrong parts
After reflow or wave soldering: less tin / more tin, no tin, short solder ball, missing material, polarity shift, pin bending, wrong components
PCB industry bare board detection

2. E-Test(electronic test)
    Flying probe test is the latest solution to some major problems in electrical test. It uses a probe instead of a needle bed, and uses a plurality of electrical probes driven by a motor and capable of rapid movement to contact with the pins of the device and conduct electrical measurement.
This instrument was originally designed for bare board, and also needs complex software and programs to support it; now it can effectively carry out simulation online test. The appearance of flying probe test has changed the test method of quick turn assembly products. Testing that used to take weeks to develop is now just a few hours, greatly reducing the product design cycle and time to market.
The combination of the automatic optical alignment system and the traditional flying needle machine makes the flying needle test more convenient and accurate with the help of the image processing software and the special flying needle alignment camera.
The electronic test for circuit boards is performed after manufactured. All the PCB manufactured by PCBBay must be checked with flying probe test.

3. Automated X-Ray Inspection
X-ray uses cathode-ray tube to produce high-energy electrons that collide with metal targets. In the process of impact, due to the sudden deceleration of electrons, the lost kinetic energy will be released in the form of X-ray. For the positions where the sample can not be detected by appearance, the change of light intensity after X-ray penetration of different density materials can be recorded. The contrast effect can form an image to show the internal structure of the object to be tested, and then the internal problem areas of the object to be tested can be observed without damaging the object to be tested.
Detection of internal cracks and foreign matters of metal materials and parts, plastic materials and parts, electronic components, electronic components, LED components, analysis of internal displacement of BGA, circuit board, etc.; identification of BGA welding defects such as empty welding and false welding, analysis of internal conditions of Microelectronics System and sealing components, cables, fittings and plastic parts.
Application scope:
IC, BGA, PCB / PCBA, surface mount process weldability test, etc.
Test steps:
Confirm the sample type / material à put the sample into the X-ray equipment for testing à judge and analyze the picture à mark the defect type and location.
According to the standard:
IPC-A-610 ,GJB 548B

4. PCB surface cleanliness test
Ion cleanliness usually refers to the ion cleanliness of circuit board. Due to the ion residues caused by various materials of printed circuit board during cleaning process, it will affect the functionality and reliability of electronic products. The most common problems caused by ion pollution are surface corrosion and crystal growth, which eventually cause short circuit and excessive current passing through the connector, resulting in the final damage of electronic products.
Several pollutants mainly come from electroplating, wave soldering, reflow soldering and chemical cleaning processes, mainly including flux residues, ionized surfactant, ethanol, aminoethanol and human sweat.

Test method for Ionic Cleanliness
4.1 Anion and cation test method
Anion and anion method is mainly used to test the cleanliness of ions, which is to soak the sample surface with a certain proportion of isopropanol and water mixed solution, so that the pollutants on the sample surface dissolve into the solution, and then analyze the pollution degree by testing the types and contents of anion and organic acid in the solution. The test results are generally expressed in UG / cm2, and the test standards refer to ipc-tm-650,2,3,28. The advantage of this method is that it can know the kinds and contents of the residual ions in detail. According to ipc-tm-650,2,3,28, the test items of anion and cation method mainly include 6 cations, 7 anions and 8 organic acids. They are:
Cation: lithium ion, sodium ion, ammonium ion, potassium ion, magnesium ion, calcium ion.
Anions: fluorine, chlorine, nitrite, bromine, nitrate, phosphate, sulfate.
Organic acids: acetic acid, adipic acid, formic acid, glutamic acid, malic acid, methanesulfonate, succinic acid, phthalic acid.

4.2 sodium chloride equivalent method
The sodium chloride equivalent method is to remove the residues left in the process from the electronic components with ultrapure extraction solution. The measurement of cleaning results is based on conductivity or resistance coefficient.
In the test, 75% IPA (isopropanol) and 25% deionized water (volume ratio) were used as the extraction solution. PCB is placed in the extraction liquid, and the conductivity or resistance coefficient of the extraction liquid after the pollutants in PCB are dissolved is measured as the basis of pollutants. Due to the different types of ions in pollutants, the ion concentration of equivalent NaCl is used as the representative in the test, that is, μ GEQ NaCl / cm2 is used to express the ion concentration of equivalent NaCl as a parameter of the degree of ion pollution. The reference standard is ipc-tm-650,2,3,25c. The disadvantage of this method is that it can not know the type and content of ion pollution clearly.

How to choose test method
In general, if you want to know the type and content of pollutants clearly, it is recommended to choose ipc-tm-650,2,3,28 anion method, which can clearly understand the source of pollutants. For example, if the content of F, Cl and Br in the test results is too high, it can be judged that the pollution source may be caused by solder resist residue in wave soldering and reflow soldering process; if the test results show that the result of organic acid is too high, it may be caused by the pollution introduced in the cleaning process with ethanol or aminoethanol. But sodium chloride equivalence law has no such advantage.
Sample requirements
In order not to affect the accuracy of the test results, the surface area of the sample is generally required to be greater than 100cm2, and the sample shall be sealed and packed to prevent secondary pollution.