Electronics (SMT / AOI) Solder joint inspection

PCB solder joints in colour: the three-ring AOI light

A good solder fillet and a bad one differ in slope, not in colour. An AOI light with red, green and blue rings at three angles turns slope into colour, so a colour camera sees joint shape at a glance.

Use lighting angle to make solder shape visible.

Parts in this setup Build this system
3D illustration of the inspection setup: PCB solder joints with an RGB AOI lightUnder the RGB AOI light (LS-AOI160, RGB build): each joint's slope shows as colour, so defects stand out as colour changes.Real camera capture
3D illustration of the arrangement · Explore it in 3D
  • LightAOI, 160 mm outside, 45 mm aperture
  • Height55 mm
  • RingsRed, green, blue at different angles
  • ResultDefects show as colour changes

The challenge

Solder joints are tiny curved mirrors. Under one white light every joint glints, and an insufficient joint can look as bright as a good one.

The inspection has to judge the 3D shape of hundreds of fillets from a single top-down image.

How it was solved

An RGB AOI light such as the LS-AOI160 in its three-colour build puts its red, green and blue rings at different elevation angles. Each part of a fillet reflects only the ring that matches its slope, so flat tops, steep sides and the shallow toe come back in different colours.

The same board, seen with a colour camera, shows good joints with a consistent colour pattern; a missing or thin fillet breaks it. The test reported clear solder detail and defects found by colour change.

Why it works

  1. 1

    Colour encodes slope: the camera sees surface angle, which is what tells a good joint from a bad one.

  2. 2

    Several lighting directions can improve coverage around components. Tall parts can still occlude joints, so validate the populated board.

  3. 3

    The 45 mm centre aperture leaves room for the lens's view straight down through the light.

Lighting application-lab image sheet

Evidence you can inspect

Visible in the images

The solder capture shows coloured reflections at joints; the separate code capture shows printed-code contrast.

What the source reports

The source describes solder detail and colour changes, without an automated acceptance study.

How to use this evidence

RGB is a multi-ring build to confirm in the quote. The code-lighting example is a separate test, not another component of the solder setup.

From image contrast to a production decision

What to validate on your part

  1. 01

    Use colour consistently

    Lock white balance, exposure and RGB channel settings.

  2. 02

    Test hidden joints

    Include tall components, board warp and joints near obstructions.

  3. 03

    Set defect criteria

    Compare known bridges, insufficient solder and good joints; do not treat colour alone as proof.

Guides

From the demo to your test bench

Parts in this setup

Build this system
AOI light, power 28 W (LS-AOI160) LightTested LS-AOI160 AOI light, power 28 W (LS-AOI160) AOI light, 160 mm outside, 45 mm aperture, 55 mm high. The test used the RGB build; say RGB in your quote.Colour: RGB multi-ring build (confirm configuration) Configuration to confirm In proposed setup High power bar light, 162 x 22 x 36 mm (LS-4BRH15016) LightTested LS-4BRH15016 High power bar light, 162 x 22 x 36 mm (LS-4BRH15016) High-power bar light, 150 × 16 mm emitting face; white for the code test. $119.00 Separate test / alternative Hikrobot MV-CA050-12GC 5MP Area Scan Camera, GigE, IMX264, Color CameraOur pick MV-CA050-12GC Hikrobot MV-CA050-12GC 5MP Area Scan Camera, GigE, IMX264, Color 5 MP 2/3" colour (IMX264, global shutter): the method needs colour. $679.00 · quote In proposed setup 25mm, F2.8, 1.1", C-mount, Macro lens (65 mm (-0.4X) to 260.4 mm (-0.1X)) (LS-KF2528M-ML) LensOur pick LS-KF2528M-ML 25mm, F2.8, 1.1", C-mount, Macro lens (65 mm (-0.4X) to 260.4 mm (-0.1X)) (LS-KF2528M-ML) 25 mm macro lens, 0.4x to 0.1x; a 60 mm field on a 2/3" sensor is about 0.14x. $319.00 In proposed setup Camera stand with XZ adjustment and glass tray, height 600 mm (LS-BT-XZ-G-6-6045) Camera test stationOur pick LS-BT-XZ-G-6-6045 Camera stand with XZ adjustment and glass tray, height 600 mm (LS-BT-XZ-G-6-6045) 600 mm column, 600 × 450 mm breadboard, XZ adjustment, glass tray and two lighting holders as listed. Proposed bench fixture; confirm loads, travel and camera/lens clamps. $359.00 In proposed setup

"Tested" identifies the part named in the source. "Our pick" is a proposed alternative or supporting part. Confirm colour, optics, controllers, power supplies, cables and mounting before ordering.

The set-up

Joint lightAOI light, RGB build (LS-AOI160)
Code lightHigh-power bar light at an angle (LS-4BRH15016)
CameraColour area scan straight down through the AOI aperture
Mounting (proposed)LS-BT-XZ-G-6-6045 · camera test station with glass tray and two lighting holders

Mount the optics with intent

The station is an optical test bench, with its two lighting holders included in the catalog listing. The 3D column and base follow the published height and footprint. Carriages, clamps and part supports are schematic: confirm camera screw pattern, lens support, light fasteners, permissible load and actual travel before ordering.

Complete the electrical system

Select a controller against the exact light voltage, drive mode and power, then confirm camera data/power/I/O cables and a suitable PC. These are not silently added to the proposed optical kit.

Build this system

Start from this setup, adapt it to your part.

The configurator opens with this study's camera, lens, light and station picked. Swap any part, check fit and price, then buy or ask for a quote.

Build this system Quote the proposed setup Explore the 3D setup

Camera and available lens CAD are published models. Lens and light envelopes use printed dimensions. The linked station uses its published base size and column height; carriage, brackets, fittings, parts and spacing are illustrative. Confirm load, travel, fasteners and clearances before ordering. Light paths explain the arrangement and do not simulate optical performance.

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Make the next trial specific.

Tell us the part size, smallest defect or tolerance, available working distance, material and line speed. Include what a good part and a reject look like.

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About this case study: the photos and camera images come from the application laboratory of the maker of the lighting and optics we sell, imaged on the parts shown; your results depend on your part, camera and set-up. This is an application-lab study, not a LumaSpec customer deployment. Source figures are reported results; proposed components require a fresh trial. The 3D scene illustrates the arrangement and does not simulate imaging performance.