Types of AXI detection technology and principles and characteristics of AXI technology
AXI detection technology type
In recent years, AXI inspection technology and its equipment have developed rapidly, from 2D inspection to 3D inspection in the past. Some systems have SPC statistical control functions, which can be connected with assembly equipment to realize real-time monitoring of assembly quality. The current 3D inspection system is divided into two categories according to the layering function: without layering function and with layering function:
(1) Without layering function
This type of equipment uses robotic hands to rotate the PCB at multiple angles to form images at different angles, and then the computer synthesizes and analyzes the images to determine defects.
(2) With hierarchical function
Computer hierarchical scanning technology can provide two-dimensional section or three-dimensional vertical scanning that cannot be achieved by traditional X-ray imaging technology.
Body performance map, and avoids the phenomenon of image overlap and confusion of real defects, can clearly show the internal structure of the measured object, improve the ability to identify internal defects of the object, and more accurately identify the location of the internal defects of the object.
There are two imaging methods for this type of equipment:
① The X-ray tube emits X beams and accurately focuses on a certain layer of the measured object. The measured object is placed on a rotatable platform. The high-speed rotation of the rotating platform makes the image on the focal plane appear on the receiver clearly. Then the CCD camera converts the image signal into a digital signal, which is handed over to the computer for processing and analysis, as shown in Figure 1.14(a).
② Focus the X beam accurately on a certain layer of the PCB, and then the image is received by a high-speed rotating receiving surface. Due to the high-speed rotation of the receiving surface, the image in focus is clear, but the image not in focus is eliminated, such as As shown in Figure 1.14(b).
Computer Hierarchical Scanning Technology
Figure 1.14 Computer layered scanning technology
(a) Layered scanning device imaging method one; (b) Layered scanning device imaging method two.
In this way, images of different levels are obtained, and then through computer synthesis and analysis, the inspection of the multilayer board and solder joint structure can be realized.
Automatic X-ray Inspection (AXI: Automatic X-ray Inspection) is a new type of testing technology. Figure 1.13 shows the inspection principle of a typical AXI system. When the assembled printed circuit board enters the inside of the machine along the guide rail, there is an X-ray emission tube above the circuit board. The X-ray emitted by the printed circuit board passes through the circuit board and is received by the detector (usually a camera) placed below. The solder joints contain a large amount of lead that can absorb X-rays. Therefore, compared with the X-rays passing through glass fiber, copper, silicon and other materials, the X-rays irradiated on the solder joints are absorbed in a large amount, and the black spots produce good images. , Which makes the analysis of solder joints quite intuitive, so simple image analysis algorithms can automatically and reliably inspect solder joint defects.
The characteristics of AXI testing are as follows:
① The coverage rate of process defects is as high as 97%. Defects that can be inspected include virtual soldering, bridging, tombstones, insufficient solder, pores, missing components, etc. Especially for BGA, CSP and other solder joint hidden devices can also be checked.
② Higher test coverage. You can check the places that cannot be checked by naked eyes and online tests. For example, if PCBA is judged to be faulty, it is suspected that the inner layer of the PCB is broken, and AXI can quickly check it.
③ Test preparation time is greatly shortened.
④ Defects that cannot be reliably detected by other test methods can be observed, such as false welding, air holes, and poor forming.
⑤ Only one inspection is required for double-sided and multi-layer boards (with layering function).
⑥ Provide relevant measurement information to evaluate the production process. Such as the thickness of solder paste, the amount of solder under the solder joint, etc.
