Open Solder Joints: How AOI Detects Visible Defects

An open solder joint leaves a component lead or termination without its intended soldered connection to the pad. When that condition is visible, AOI can help find it before the assembly moves to the next stage.

The challenge is separating acceptable solder appearance from a defect. A useful inspection method needs to handle both, including the variations found across different boards and components. Here is how color rules approach that task and how DaoAI's pretrained 2D model handles open solder defects.

What is an open solder joint?

An open solder joint lacks the intended soldered connection between a component lead or termination and its pad. AOI examines visible evidence of that condition in the inspection image. During review, identify the affected termination and inspect the connection area against the assembly's acceptance criteria. Electrical continuity is checked through electrical testing.

Several solder defects can occur around the same termination. Keeping the classifications clear helps engineers prepare consistent training samples and review inspection results.

How does color based AOI evaluate a solder joint?

A color based rule measures selected colors inside a region of interest, or ROI. It can count matching pixels or calculate their share of the region, then compare that measurement with an acceptance limit. The result depends on the captured image, the chosen region and the rule settings. Lighting and camera configuration therefore need to remain consistent.

A simple color area check has four steps:

1. Capture the joint under the configured lighting and camera settings.
2. Position the ROI over the inspection area.
3. Count pixels within the selected color range.
4. Compare that count or proportion with the configured limits.

Where do fixed color thresholds run into trouble?

Fixed color thresholds become difficult to set when acceptable and defective joints produce similar measurements. Widening the range can reduce false calls while also admitting defects. Tightening it can catch more defects while rejecting acceptable joints. The practical question is whether the selected measurement separates the two groups across the boards and conditions you need to inspect.

Two situations are worth checking:

• An acceptable joint looks different. A change in lighting or camera settings changes the recorded colors. The matching pixel count moves outside the acceptance range, creating a false call.
• A defective joint passes the color check. Its selected pixels still fall inside the accepted range, while a visible problem elsewhere in the connection area needs attention.

How does DaoAI's pretrained 2D model help?

DaoAI's pretrained 2D model covers most common open solder cases and can be used directly. For special cases, add the relevant samples in the software and train the model to correct how those cases are classified.

See the in software model training workflow.