Lead frame inspection: one scan, five images — separating scratches and dents from glare
Lead frames are highly reflective and full of texture, so a single light causes false calls. With an 8K line-scan camera and multi-light compositing, defects of 0.03–0.05 mm are detected at 10 μm resolution.
The lead frame is the skeleton of an IC package. Scratches, dents, missing plating and foreign matter on its surface directly affect wire bonding and packaging yield. But metal reflects strongly and etched textures are everywhere: a single photo from an ordinary camera either hides the defect or fills the screen with false calls.
Shin Shou has evaluated lead frame and metal substrate inspection for two packaging-material customers. Here is the approach and the data we converged on.
One scan, five to six lighting conditions
We use an 8K or 4K monochrome line-scan camera on a motorised stage moving continuously, switching between illumination conditions during the scan. One pass yields five or six images of the same position under different light. Scratches are clearest under one light, dents and pits under another, and the images are judged together.
Validation results
- Detected water marks, scratches, foreign matter, residual adhesive, abrasion, dents, deformation, V-groove contamination and missing plating
- After multi-light compositing, false calls on scratches, dents and abrasion dropped clearly; some pits only appear under one specific light
- 8K camera at 10 μm: detection capability about 0.03–0.05 mm (3–5 pixels)
- 4K camera at 21 μm: about 0.06–0.15 mm, suitable for products with a 0.1 mm specification
- Colour-type defects such as missing plating can be detected even with a monochrome camera when light intensity is controlled
Estimating cycle time
For a 70 × 105 mm lead frame, a 4K line scan needs about 6,300 lines — roughly 1 second — and computing five defect types takes about 0.7–1 second. With a 25 MP area camera at 20 μm using move-and-stop at two positions with two lights, the total is about 1.3 seconds. Line scan or area scan depends on part size, resolution and line takt.
Recommendations
Where textured and functional areas have similar grey levels, inspection conditions must be set per zone, with no-inspect areas defined, to avoid false calls. We suggest sending 3–5 samples of each defect type so the free assessment can fix resolution and lighting before machine design starts.
