BGA is an essential part of electronic components. Sometimes, voids often appear in BGA packaging and welding. The main cause of voids is that the organic matter in the flux is cracked at high temperatures to generate bubbles, causing the gas to be surrounded in the alloy powder and forming voids. Soldering voids are likely to cause poor contact with electronic components during later use and affect the service life. In this article, we will share common methods for detecting BGA solder joint defects to help make better judgments.
Non-destructive detection method
Visual inspection
Visual inspection can be carried out during the entire production process of electronic products. Observe solder joints through a high-power magnifying glass, and initially detect whether there are obvious defects in solder joints from the appearance.
- Purpose:
To observe the solder joint simply, quickly and intuitively, and check whether there is continuous welding on the outside of the solder joint and the surrounding surface.
- Shortcoming
However, visual inspection has great limitations. It can only be used as a preliminary judgment when we do not have other testing equipment. It is impossible to judge whether there are other defects inside the solder joint or whether there are holes on the surface of the solder joint.
X-ray inspection
Radiographic inspection is a non-destructive physical perspective method, which uses X-ray perspective components to detect bubbles, cracks, and abnormal bonding lines in the internal packaging of components without destroying the chip.
(1) 2D X-ray
Records the light intensity changes after X-rays penetrate materials with different densities for the position of the sample that cannot be detected by the naked eye. Then it can form a contrasting image, showing the internal structure of the measured object. Problems can be observed without destroying the object.
- Purpose
To observe defects such as empty soldering, virtual soldering, internal displacement analysis, bridging, and short circuits of BGA soldering by X-ray scanning.
- Shortcoming
It only observes two-dimensional plane images. The principle is to display a three-dimensional sample on a two-dimensional display for imaging. For products with complex structures, the information in different depth directions overlaps, which is easy to confuse.
For example, when the components are on different surfaces at the same position, the shadows formed by the solder will overlap, which will affect the accuracy of the test results, so it is often used as a preliminary rapid determination of products with complex structures.
(2) 3D X-ray (CT scan)
3D X-ray better covers 2D X-ray limitations and presents three-dimensional images with high-density resolution and high spatial resolution. Besides, it can also realize simulated tomography images.
- Purpose
To clearly and accurately observe the soldering quality and structural defects of BGA solder joints. It enables to display of the shape, location and size of soldering internal defects.
- Shortcoming
Using the above non-destructive testing methods to detect solder joint defects, both visual inspection and 2D X-ray have limitations. 3D X-ray (CT scanning) is the most advanced non-destructive testing technology at present, which can solve the problem of solder joint defects well.
Destructive detection method
Red ink test
The red ink test is suitable for verifying the solderability of BGA and IC on printed circuit boards. Soldering cracks can be judged by observing and analyzing the dyeing of solder joints of printed circuit boards and integrated circuit components.
The principle of the red ink test is to use the permeability of the liquid. Put the solder joints in the red dye, let the dye penetrate into the weld cracks, and the dry solder joints are forced to separate, and judge whether the solder joints are broken by observing the color state of the crack interface.
Simply, it is divided into five steps: cutting→infiltration→drying→separation→observation
- Purpose
In general, the red ink test can see the soldering phenomenon of all solder balls under the entire BGA. It is a common method to analyze the welding quality of electronic components. It can check whether there are defects such as virtual welding, false welding and cracks in the welding process of electronic components.
Slice analysis
Slice analysis technology is an important technology for PCB/PCBA failure analysis.
The steps of slice analysis technique are: Sampling→cleaning→vacuum mounting→grinding
→polishing→microetching (if necessary)→analysis.
The quality of slices will directly affect the accuracy of fault site confirmation, so the ability of inspectors is highly required.
- Purpose
It can be used to detect internal voids of PCBA solder joints, interface bonding status, wettability evaluation and circuit board quality.
SEM&EDS combination
On the basis of slice analysis technology, if you want to know the cause of solder joint defects, SEM&EDS can be also used to analyze the cause of failure.