Inspection of components and PCBAs
There are some different ways to inspect defects in components, solder joints and the structure of PCBAs and perform audits like IPC-A-610.
Optics
Visual inspections using optical microscopes and stereoscopes are essential for identifying defects in electronic components, solder joints, PCBA and printed circuit boards (PCBs). These inspections involve a meticulous examination process where various contrasts and filters are employed to enhance the visibility of different structural elements in the samples.
Tools
Optical microscopes provide high magnification and resolution, allowing technicians to detect minute flaws that are not visible to the naked eye. Stereoscopes, on the other hand, offer a three-dimensional view, which is particularly useful for examining the topography of solder joints and the overall layout of PCBAs.
By utilizing different contrasts, such as brightfield, darkfield, and phase contrast, inspectors can highlight specific features of the samples. Filters can further enhance these contrasts, making it easier to identify issues like cracks, voids, and other irregularities.
In addition to visual inspection, these tools enable precise measurements of areas of interest. This capability is crucial for quality control, as it ensures that components meet their specifications. Measurements can include dimensions of solder joints, spacing between components, and the thickness of PCBA layers.
X-Ray
Useful to internal inspections of components, solder joints and PCBAs without destroying the samples. As well, reconstructions like tomography and laminography can be performed to inspect areas of interest with a high density of components. Level of voiding, coverage area on pads and barrel filled in PTH components can also be quantified.
Tools
Metallographic Cross-Sections
Internal inspection of components, soldering joints and PCBAs by cutting and polishing to the area of interest. The interior of the solder joints is evaluated to determinate the quality of the joints (intermetallic layers and metallographic structure), and to look for defects such as cracks, voids, oxidations, etc. and the interior of the PCBA for example, for delamination, cracks on barrels or vias, etc. Also, some contrast and filters can be used to inspect different areas of interest, like the intermetallic phase, and measure them.
Tools
SEM (Scanning Electron Microscopy)
Inspection using high-resolution electron microscopy of components, soldering joints, PCBAs and cross sections to determinate the quality of the metallic finishes, the intermetallic layers and the metallographic structure of the joints. Also, to look for defects such as cracks, voids, oxidations, whiskers, dendrites, etc.
Elemental analysis can also be performed to identify the chemical composition of the samples or residues.
Tools
SAM (Scanning Acoustic Microscopy)
Inspection using ultrasounds to inspect internal structures for voids that are not visible in X-rays, in encapsulated components and PCBAs, without damaging the samples.
Decapsulation
This involves removing the encapsulation of an electronic component to expose and analyse its internal structure. It can be useful to look for defects or counterfeits.
The exposed die can be inspected by optical or SEM to look for defects or manufacturing mark. Additionally, thermography tests are very useful to locate hot spots in an exposed die.
