X-ray inspection technology is a key tool in PCBA quality control, capable of effectively identifying soldering defects that are difficult to detect using traditional inspection methods. This article provides a detailed overview of the principles, methods, and application process of X-ray inspection.
I. Principles of X-ray Inspection
X-rays are electromagnetic waves with extremely short wavelengths and very high energy. When X-rays are directed at a sample, their transmission intensity depends not only on the energy of the X-rays but also on the density and thickness of the sample. The lower the density and the thinner the sample, the easier it is for X-rays to penetrate it.
The principle behind X-ray inspection involves irradiating a sample with X-rays and then using image acquisition and conversion equipment to map the intensity of the transmitted X-rays onto a grayscale image of the PCB. The PCB contains information on various thicknesses, which are generally classified into four categories based on data density:
(1) Solder joints composed of high-density tin, lead, or tin-lead alloys;
(2) Data on metal and ceramic packaging housings, gold wires, and wafer bonding;
(3) Magnetic materials, such as molded plastics and silicon;
(4) Defects such as voids, cracks, and PCB through-holes.
When X-rays pass through the first and second types of data, fewer X-rays pass through, resulting in images with higher grayscale values; when X-rays pass through the third type, the resulting images have lower grayscale values; for the fourth type, the X-rays pass through completely, resulting in a bright image.
II. X-ray Inspection Process
The 2D X-ray detector can be tilted ±70°. First, adjust the voltage, then adjust the X-ray detector’s power and contrast to optimize image quality. The entire inspection process is divided into four main steps, referred to in this paper as the “3+1” method:
(1) Perform a comprehensive inspection of the PCB, primarily covering the PCB and its components;
(2) Enlarge the image for a detailed examination to identify defects or suspected defects;
(3) Identify, analyze, and confirm suspected defects through magnification and oblique imaging;
(4) Perform tilt imaging on all BGA-packaged devices to conduct a preliminary inspection for solder joint defects.
III. Advantages of X-ray Inspection
This inspection scheme addresses the current challenge of detecting hidden soldering defects in PCBs using conventional two-dimensional X-ray inspection systems. It proposes an inspection method and process, and the X-ray inspection scheme has been validated through experiments. The results indicate that the X-ray inspection scheme is reasonable and feasible. Based on this scheme, PCBs with common soldering defects can be identified, and it can also guide improvements in PCB design and soldering processes.
X-ray inspection solutions offer the following advantages during inspection: clear imaging that makes defects easy to identify; coverage of common PCB defects, ensuring high-quality results; and standardized operating procedures that ensure high inspection efficiency.
IV. The Importance of Quality Control
Strict control over product quality not only reflects a company’s commitment to providing high-quality production services but also serves as a strong safeguard for industrial safety. Strengthening quality inspections of castings and ensuring production quality are key to guaranteeing the sustainable development of China’s manufacturing sector.
