Conformal coating inspection (CCI) AOI system

01

Make the coating visible: UV tracer, lighting and where the machine sits

ACI Technologies' technical tip on conformal coating inspection explains that when a coating contains a UV tracer dye, inspection can be done under an ultraviolet light source, which makes it possible to verify complete coverage and any areas specified to stay free of coating, such as electrical contacts. It lists the five coating types as acrylic (AR), epoxy (ER), silicone (SR), polyurethane (UR) and paraxylylene (XY), notes that J-STD-001 requires coatings to be fully cured, homogeneous and free of delamination exposing conductive surfaces, and that magnification up to 4X may be used for visual checks. [3]

Mek's CCI systems use UV light to bring out discrepancies, contamination and process issues after manual spray, automatic spray and dip coating; Mek lists a high-intensity UV source tuned to 365 nm fluorescence, a 24-bit colour camera, and lighting modes of white only, UV only, white plus UV, and white and UV-white, with programming from a library or golden components. [2] Viscom's iS6052 CCI uses integrated UV LEDs to raise contrast between coated and uncoated areas, offers premium high-power LEDs for silicone-containing or thinly applied coatings that reflect less, and supports wet inspection before the coating cures as well as dry inspection. [1]

Editorial note: tell the supplier the coating chemistry, whether it contains a UV tracer and at what wavelength it fluoresces, and whether you want to catch defects wet — before curing, when rework is easier — or dry, after cure.

Give the supplier the coating type and supplier, UV tracer and fluorescence wavelength, application method (spray, dip, selective), keep-out areas, required thickness range, wet or dry inspection point, board size and tallest component, line speed, and how defects should be logged and sent to rework.

02

Check camera resolution, field of view and how thickness is verified

Viscom specifies the iS6052 CCI with an orthogonal camera at 12 µm resolution and a 50 × 50 mm field of view (an 8M camera option gives 15 µm over 38.9 × 29.2 mm), no angled megapixel cameras in the base configuration, an upper transport clearance of up to 115 mm, board dimensions of 440 × 508 mm with a long-board option up to 720 mm, and a system housing of 997 × 1756 × 1753 mm. Its inspection scope covers dry and wet inspection, integrity of coated areas, layer thickness measurement, and defects including splatter, smearing, scratches, blisters and orange peel. [1]

Thickness limits differ by resin: ACI Technologies cites J-STD-001 as specifying 0.03–0.13 mm for AR, ER and UR coatings, 0.05–0.21 mm for SR coatings and 0.01–0.05 mm for paraxylylene, measured either dry with a micrometer on a test coupon or flat cured surface, or wet before cure with a calculation of the cured thickness. [3] HumiSeal's planning guide gives 25–75 µm dry film for acrylic, urethane and silicone liquid coatings, 5–25 µm for parylene and 60–130 µm for UV-curable coatings (80–110 µm in automotive use), and stresses that these are planning ranges, not specifications. [4]

Editorial calculation: covering a 440 × 508 mm board with 50 × 50 mm fields needs 440 ÷ 50 = 8.8 → 9 and 508 ÷ 50 = 10.2 → 11 fields per axis, at least 99 field positions before overlap. At 12 µm per pixel, the thinnest J-STD-001 acrylic layer of 0.03 mm (30 µm) spans 2.5 pixels — a lateral comparison only, since the camera looks down on the coating rather than through its thickness; ask how the system's thickness measurement works and how it is checked against coupon measurements. [1] [3]

03

Coating defects a CCI programme should name

04

Machine values to state for a CCI enquiry

Speed and false-call figures depend on your coating's fluorescence and board layout, so ask for results on sample boards coated with your own material.

05

Describe the coating and where it is checked

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Coating: [chemistry; supplier; UV tracer and wavelength]
Application: [spray; dip; selective; cure method]
Areas: [must-coat areas; keep-out areas]
Thickness: [required range; measurement method]
Inspection point: [wet; dry; in-line or stand-alone]
Board: [size; tallest component; line speed]

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