BGA defect detection: packaging process and component solder joints

Date：2021-09-06 17:17:06Views：1482

With the continuous progress of science and technology, modern society is closely related to electronic technology. It is unable to effectively ensure the product qualification rate of its electronic components, especially for packaging companies (such as BGA). The quality of solder joints is very important to determine the reliability and performance of SMT components, and the quality of BGA Solder Joints should be the key. Therefore, it is very important to take effective measures to ensure the solder joint quality of BGA components and realize the final reliability of SMT components.

BGA introduction packaging technology

BGA packaging technology began as early as the 1960s and was first applied by IBM. However, BGA packaging technology did not enter the practical stage until the early 1990s.

The limitation of fine pitch element is that its lead is easy to bend, break and damage, which puts forward high requirements for the coplanarity and installation accuracy of lead. BGA packaging technology adopts a new design thinking model, that is, circular or cylindrical solder balls are hidden under the packaging, with large wire spacing and short wires. Therefore, BGA packaging technology can solve the common coplanarity and warpage problems in fine pitch components.

Therefore, the reliability of BGA module and the performance of SMT module are better than ordinary SMD (surface mount device). The only problem with BGA components is that it is difficult to test solder joints and ensure quality and reliability. Therefore, solder joint problems of BGA components are very common.

So far, reliable electronic assemblers such as pcbart and BGA components have been exposed through electronic testing. During the assembly of BGA components, other methods to control the quality of assembly technology process and determine defects include slurry screening, Axi sample test and electronic test result analysis.

Meeting the quality evaluation requirements is a challenging technology because it is difficult to pick up the test point under the package. In the defect detection and identification of BGA components, electronic testing is usually not carried out, which increases the cost of elimination and rework to a certain extent.

During the defect detection of BGA components, the electronic test can only judge whether the current is on or off after connecting the BGA components. BGA assembly is a basic physical connection process. In order to confirm and control the quality of technical processes, physical components must be understood and tested to affect their long-term reliability, such as solder paste volume, wire and pad alignment and wettability.

Method of checking BGA elements

Test the physical properties of BGA assembly solder joints and determine how to continue to contribute to reliable connection during process research. The feedback information provided by all tests is related to the modification of each technical process or solder joint parameters.

The equipment will be used for X-ray inspection, and the solder paste on the pad represents a shadow image because the solder paste is above the solder joint. For non foldable BGA components, the front solder ball may also have shadows, which undoubtedly makes it difficult to determine. This is because the shadow effect caused by solder paste or front solder ball hinders the work of X-ray inspection equipment, which can only roughly reflect the process defects of BGA packaging. In addition, peripheral inspection also faces challenges such as insufficient solder paste or open circuit caused by pollutants. X-ray inspection technology can overcome the above limitations. It can check the hidden defects of solder joints and display the connection of BGA Solder Joints.

Basic defects of BGA Solder Joint

1. Open circuit

Due to pad contamination, the non foldable BGA Solder Joint will always have an open circuit. Since the solder paste cannot wet the pad on the PCB (printed circuit board), it will climb to the component surface through the solder ball. As mentioned above, the electronic test can determine the open circuit, but it cannot distinguish whether the open circuit is caused by pad contamination or solder screening defects. The X-ray testing equipment can not indicate an open circuit, which is caused by the shadow effect of the front solder ball.

Cross section X-ray detection technology can capture slice images between pads. Component and then confirm the open circuit due to contamination. Because the open circuit caused by pollutants produces fine pad diameter and relatively large component diameter, the difference between component diameter and pad diameter can be used to determine whether the open circuit occurs due to pollution. As for the open circuit caused by insufficient solder paste, only the cross-section detection device can be manufactured.

2.Void

Since the flowing steam stays at the solder joint of low eutectic point, foldable BGA element welding will occur. Voids can be considered as a major defect in foldable BGA components. During reflow soldering, the flotation caused by voids is focused on the element surface, so most solder joint failures also occur there.

By preheating and increasing, the gap problem can be eliminated, and the transient preheating time and low preheating temperature during reflow welding can be eliminated. Once the gap exceeds a certain size, quantity or density range, the reliability will certainly be reduced. However, another school believes that gaps should not be limited, but their rupture and expansion should be accelerated so that they can be found and eliminated as soon as possible.

These can be tested by X-ray nondestructive testing equipment. Nowadays, nondestructive testing in the domestic market includes X-ray testing, ultrasonic testing and magnetic particle testing. Among these types of tests, X-ray test is the most popular test among users. The X-ray test will not cause any damage to the internal structure of the product, and the detection accuracy is very high. The internal defects of the product can be accurately detected mainly through the X-ray penetration principle.