PCB Technical - How to check the coating quality of PCBA

1, Conformal coating

PCBA coating should be transparent and cover PCB and components evenly. Whether the coating is uniform or not is related to the coating method to a certain extent, which will affect the appearance of printed circuit board surface and the coating condition of corners. In SMT SMT chip processing, there will be a "deposition line" of coating accumulation or a small amount of bubbles at the edge of the board, which will not affect the function and reliability of the coating.

How to check the quality of PCBA conformal coating

2, Coating

The coating on PCB can be inspected by naked eyes. The coating with fluorescent material can be inspected in dim light, and white light can be used as auxiliary means for coating inspection.

(1) Objectives

It has good adhesion on PCBA components; there is no bubble or bubble.

There is no semi wetting, powder particles, peeling, wrinkle (non attachment area) cracking, ripple, fish eye or orange peel peeling through PCBA detection.

No foreign impurities; no discoloration or transparency reduction; the coating is completely cured and uniform.

(2) Acceptable

The coating layer is completely cured, uniform and uniform; the area to be coated is covered by coating; there is no adhesion to the solder mask.

There is no adhesion loss, no cavity or bubble, no semi wetting, no crack, no wavy mark, no fisheye or orange peel off at the jumper of adjacent pad or conductor surface on PCB; foreign objects do not affect the electrical gap between components, pads or conductor surfaces.

The coating is thin, but it can still cover the edge of components.

(3) Defects

. coating not cured (showing stickiness)

. areas requiring coating are not coated.

. coating missing in areas requiring coating.

Due to obvious adhesion loss (powder particle), cavity or bubble, semi wetting, crack, ripple, fish eye or orange peel peeling at the jumper of adjacent conductor or PCB pad, bridging the surface of pad or adjacent conductor, exposing the electric gap between the pad or conductor surface of influence component. Discoloration or loss of transparency.

3, Thickness of conformal coating

The sample can be the same material as PCBA,PCB, or other non porous materials, such as metal or glass. Wet film thickness measurement is also a method of coating thickness measurement. It obtains the final coating thickness according to the known dry / wet film thickness conversion relationship.