Solder joint inspection
Solder joint inspection is a crucial step in electronics manufacturing. It is used to check the quality of the solder joints to ensure that electronic components function reliably and are free from defects.
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For what is solder joint inspection used?
Solder joints are critical connections that electrically and mechanically connect electronic components to a printed circuit board (PCB). Deficient solder joints can lead to failures in electronic devices, which can result in costly repairs or even safety problems. Solder joint inspection is therefore essential for ensuring the reliability and durability of electronic assemblies.
Solder joint inspection
at Quality Analysis
High resolutions in the micro and nanometre range are required for the precise inspection of components and solder joints. In addition to light and electron microscopy, non-destructive methods such as 2D X-ray analysis and 3D computed tomography offer fast and effective ways of detecting hidden defects. We offer non-destructive as well as destructive analyses and combine advanced technologies for a comprehensive analysis and quality assessment.
- Non-destructive inspection by means of 2D X-ray inspection and 3D computed tomography
- Non-destructive or partially destructive inspection using light microscopy, scanning electron microscopy and FIB-SEM microscopy
- Serial inspection for good/bad checks
- Analysis of solder joints, e.g. distance between the balls of solder, solder climbing or solder gap thickness
- Irradiation at an angle for the analysis of wetting and dewetting defects
- Analysis of solder joint anomalies, e.g. excess solder, pin holes, cracks, pores and shrinkage cavities, bridge formation or fractures in the solder joint
- Determination of portion of pores (voids) in solder joints or conductive adhesives
- Automatic solder joint inspection (AXI) of, e.g., BGAs, gullwing pins or integrated circuits (ICs)
- Analysis based on acceptance criteria for printed circuit boards and electronic assemblies, e.g. IPC A-600 and IPC A-610
Which methods are used for solder joint inspection?
The inspection methods used for solder joint inspection are varied. A small selection of the methods related to practice is presented here.
Manual optical inspection (MOI)
MOI involves the manual inspection of solder joints for obvious defects such as uneven solder joints, cold solder joints or visible solder bridges. Although this method can assist with the detection of major defects by using microscopes, its effectiveness is limited, especially for modern printed circuit boards with fine-pitch components. Many defects often remain undetected, which is why visual inspection is usually supplemented by advanced technologies such as automated optical inspection (AOI) or automated X-ray inspection (AXI).
Automated optical inspection (AOI)
AOI is a key method for solder joint inspection. It uses high-resolution cameras and advanced image processing technology to inspect solder joints precisely. AOI systems acquire detailed images of printed circuit boards and analyse them for visual defects such as solder bridges, insufficient wetting or other irregularities. AOI is particularly advantageous for series production, because it permits the fast, consistent, objective evaluation of solder joints.
Automated X-ray inspection (AXI)
AXI is an advanced inspection method that makes it possible to inspect solder joints that cannot be checked using optical methods. It is used in particular for complex assemblies such as ball grid arrays (BGA) and other concealed joints. AXI systems use X-rays to create a penetrating view of the solder joints, permitting the detection of internal defects such as voids, insufficient wetting, solder bridges and shrinkage cavities. Modern AXI systems can work in 2D, 2.5D and 3D.
Goals of solder joint inspection
Solder joint inspection is a crucial analytical method when it comes to quality assurance on electronic components. The primary purpose of the inspection is to ensure that all solder joints meet the required electrical and mechanical standards. In this way, it helps to detect solder defects at an early stage and prevent consequential damage.
Making solder defects visible
While inspecting solder joints, it is possible to identify various types of defect that jeopardise the functionality and reliability of electronic assemblies.
A frequently occurring defect is the cold solder joint, which is caused by insufficient heating during the soldering process and can lead to weak or missing electrical connections.
There is also the solder bridge, where neighbouring solder joints are unintentionally connected together, which can result in potentially dangerous short circuits. These types of defects are detected particularly effectively by automated optical inspection (AOI) or X-ray inspection (AXI).
Another problem is shrinkage cavities, which form inside the solder joint. These degrade both the mechanical strength and the electrical conductivity of the joint. The AXI method is particularly well-suited to the detection of these internal defects.
In addition, cracks, which are often caused by mechanical loads or thermal cycling, can significantly weaken the solder joint. These cracks can be detected by visual inspections and special inspection methods such as thermal cycle testing and X-ray inspection.
Finally, corrosion is also a risk, especially in damp or aggressive environments. It poses a serious risk to the durability and reliability of the solder joints. Areas with corrosion can be detected by visual inspection or chemical analyses.
Solder joint inspection in practice
In practice, solder joint inspection is undertaken on a large number of electronic components and assemblies to ensure the quality and reliability of the joints. It is used particularly frequently for the inspection of printed circuit boards (PCBs), where it checks the solder joints on surface-mounted components (SMDs) such as resistors, capacitors, integrated circuits (ICs) and transistors. Solder joint inspection is also essential for sophisticated components such as ball grid arrays (BGAs) and quad flat no-leads packages (QFNs), because defects such as solder bridges or cavities are often not visible and require specialised methods such as X-ray inspection (AXI). Inspections are also undertaken on through-hole components (THT), particularly where components are subjected to high mechanical loads, such as in connectors or power electronics.
In summary: solder joint inspection
Solder joint inspection is a central element of quality assurance in electronics manufacturing. By means of the targeted use of various inspection methods, solder defects can be identified reliably, ensuring that components such as printed circuit boards and BGAs meet high requirements for reliability and safety.
