NOT ALL SOLDER JOINTS ARE THE SAME.
Optical inspection of solder joints has increasingly moved into focus for many users in recent years. The specific soldering method — whether wave, hand, or laser soldering — plays no significant role in the evaluation. However, in most cases 2D imaging is no longer sufficient, as aspects such as volume and meniscus angle also need to be verified. Our solder joint inspections are based on IPC-A610 standards, and we’d like to give you a brief insight into this process below. The optimal hardware for this comes from Keyence.
Verification of solder joint quality according to NPC Guidelines
SOLDERING TESTING
The quality assessment of solder joints is defined in the IPC guidelines. Using modern 3D imaging technology, these criteria are evaluated within fractions of a second.
Percentage wetting of the solder pad:
A ring-shaped region of interest (ROI) is placed around each affected solder joint.
A ring set directly outside the region of interest (ROI) is used as a reference plane for height adjustments.
Height extraction is set to 0.01 mm per gray level. The visible area is measured at elevations of 0.25 mm above the PCB surface and converted to metric.
Enclosure of the pin to be soldered:
For each corresponding solder joint, 36 individual height profiles are generated rotating around the solder joint by 10 degrees offset:
For each height profile, at 0.15 mm above the surrounding PCB surface, the distance between the outer contour and the contour center is measured. If this distance exceeds the corresponding pin radius, the profile is classified as wetted. The number of wetted profiles is then determined. As recommended by the standard, at least 27 valid profiles are used as a tolerance, with each profile covering 10 degrees.
Volume of the solder
The convex volume of each solder joint is determined, using the immediate surrounding area as the reference plane. For this purpose, the Z-integral of all pixels above the reference plane within the inspection area is calculated. This volume inherently represents the volume of the pin to be soldered.
Meniscus angle of the solder at the soldering point
As with the wetting inspection, 36 height profiles are generated for each solder joint at rotational intervals of 10 degrees.
In each profile, the angle between the right contours is measured within the height range of 0.25 to 0.6 mm.
The result is given as the average of the measured angles.
Holes
The surface concave below the zero plane is evaluated:
If the entire concave surface is larger than the tolerance stored in the variable <#Hole_Area>, this soldering point is rated as NOK.