bubble

 

When there are bubbles in the three-proof paint, we must first understand the type of the three-proof paint, the viscosity and thickness of the three-proof paint, the coating and curing equipment, and the coating process.

Large bubbles appear in solvent-based three-proof paint, mainly because the furnace temperature is too high, the surface layer is fast skinned, too much solvent remains in the paint film, and the solvent under the surface layer is quickly volatilized, or the three-proof paint is too viscous If the thickness is too high, the bubbles cannot be released quickly. The solution to this kind of large bubbles is: optimizing the furnace temperature curve and reducing the slope of the furnace temperature curve; increasing the volatilization of the leveling solvent before curing, such as increasing the self-drying time before baking; reducing the amount of glue when coating, Such as reducing the overlap coating area.

Small bubbles appear in the solvent-based conformal paint, mainly in the compressed air paint tank coating method. The solution is mainly to reduce the air pressure of the paint tank or change the type of thinner, and then consider the curing oven temperature and leveling before curing. The factor of solvent volatilization.

UV three-proof paint has bubbles. Most UV three-proof paints do not contain solvents or contain a small amount of solvents, but leveling and volatilization are still necessary. It is not recommended to use compressed air paint tanks and atomized coating. It is recommended to use membrane pumps. To reduce the air being pressed into the paint, in addition, it is recommended to stand for 1 hour after adding the paint.

 

 

Whitish

 

The coating film of the three-proof paint contains water or other liquids, the color of the coating film is lighter than the original, and the coating film appears white foggy. The main reasons are: (1) The moisture content of the board is too high, and the moisture volatilizes over time and stays in the paint film to cause whitening; (2) The environmental humidity is too high; (3) PCBA surface, container, and three-proof paint Mixed with water; (4) The thinner evaporates too fast. The main solutions are: (1) Dry the board before construction to control the moisture content of the board. (2) Do not apply the three anti-coating paint with one-time thick coating; (3) Do not apply when the humidity is high. Add it if necessary. Appropriate slow-drying solvent (4) The surface of PCBA should be clean and free from moisture; (5) The three-proof paint and the container should not be mixed with moisture.

 

Stratification

 

The delamination of the three anti-paints mainly appears on the components and the solder mask. In the entire PCBA production process, coating the three-proof paint is the last process. Most PCBA that needs to be coated with the three-proof paint are not cleaned. There will be a lot of chemical residues on the board, such as additives in the solder resist. Used to improve the surface quality (such as beautification, increase abrasion resistance, increase wettability, etc.), these additives will have a compatibility impact on the conformal coating. The main method is to consider cleaning the board and reducing the film thickness. As for the delamination caused when the protection is removed, it is due to the poor adhesion of the three-proof paint. It is recommended to remove the protection when the coating is dry to the touch (the coating is still soft).

 

Orange pattern

 

The orange streaks of the three-proof paint are caused by forced drying. The solution is mainly to check the production environment, such as temperature and humidity; reduce the emission of the leveling volatilization area before curing; reduce the viscosity of the three-proof paint; reduce the climbing slope of the furnace temperature curve; use a thinner with a slower volatilization speed.

 

 

Cracks and scratches

 

The cracks in the three-proof paint are mainly due to the excessive thickness of the film, and the excessive surface tension of the pins and the edges of the components. The solution is to reduce the film thickness, optimize the furnace temperature curve, the furnace temperature should not be too high, and let the paint film slowly dry and solidify to achieve the best performance. The scratches come from the scratches of the tools or machinery during the coating process. Special care should be taken during the coating and drying process and the packaging process.

 

Capillary phenomenon

 

The capillary phenomenon of the three-proof paint comes from the following aspects: 1. Small-pitch tube leg connectors during board design; 2. Too harsh coating requirements; 3. Three-proof paint viscosity is too low; 4. Three-proof paint flow is too high Large; 5. The surface tension of the substrate and the conformal paint is inappropriate. The solution is: 1 increase the distance between the coating area and the connector; 2 use masking glue around the connector to form a fence; 3 use a higher viscosity three-proof paint; 4 reduce the film thickness; 5 clean the board due to various reasons When the circuit board is coated with one or more coverage defects, specific problems must be analyzed and resolved one by one.