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Working Principle of X-ray Inspection Machine

With the rapid advancement of electronics technology, SMT technology has grown in popularity, chip sizes have shrunk, and chip pin counts have increased, particularly in recent years, as evidenced by the appearance of BGA chips. Because the pins of BGA chips are not distributed around the chip as they are in traditional designs, but rather on the bottom side, there is no doubt that traditional manual visual inspection will not be able to judge the quality of the solder joint and it will need to be tested with ICT or even functional testing. However, batch faults are difficult to detect and current in a timely manner, and manual visual inspection is the least reliable and repeatable technology. Because X-ray inspection technology is becoming more frequently employed in SMT quality inspection after reflow, it not only provides for qualitative and quantitative analysis of solder junctions, but also for the prompt detection and correction of problems.

1. The X-ray inspection machine's working principle

The X-rays released by the X-ray inspection machine transmitter tube located above the plate travel through the plate and are received by the detector (typically a camera) placed below when the plate enters the machine along the guide rails. Because the solder joint contains lead, which absorbs a large amount of X-rays, the X-rays that hit it are absorbed to a greater extent than those that pass through other materials such as glass fiber, copper, silicon, and so on. And it can produce a clear image as a black spot, making the analysis of the solder joint quite simple and intuitive, so that a simple image analysis algorithm can automatically and reliably check the solder joint for detects.

2. X-ray inspection machine technology

The present 3D inspection approach has been enhanced from the previous 2D inspection method used by X-ray inspection machines. The former is a projection X-ray inspection method, which can produce a clear visual image of a single panel during solder joints. But the current widespread use of double-sided reflow boards has a poor effect, causing the two sides of the visual image of the solder joints to overlap and be extremely difficult to distinguish. The latter 3D inspection method, on the other hand, employs a layering process in which the beam is focused on any layer and the associated image is projected onto a revolving receiving surface at high speed. The image at the focal point is particularly clear due to the high-speed rotation of the receiving surface, while images on the other layers are erased, allowing the 3D inspection approach to scan solder junctions on both sides of the board separately.

In addition to inspecting double-sided solder boards, electronic X-ray machine technology can inspect unseen solder joints such as BAGs in multi-layer image slices. The top, middle, and bottom of the BGA solder ball joint can be thoroughly inspected, while through-hole PTH solder joints can also be measured using this method to check whether the solder is full in the through-hole, greatly improving the solder joint connection quality.

Combining the above factors, the X-ray inspection machine can evaluate the size, shape and characteristics of each solder joint, and automatically detect unacceptable and critical solder joints. Critical solder joints are solder joints that cause premature product failure, although these critical solder joints are considered good solder joints on other tests.

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