Surface Energy: Surface Preparation Before Conformal Coating

A coating adheres because it wets the surface and then cures in contact with it. Where the surface energy is too low or a contamination layer sits on it, the coating sits on top instead of bonding, and the failure appears at a temperature or humidity extreme.

Why Surface Energy Decides Adhesion

A liquid spreads on a surface whose energy is higher than its own surface tension. The coating formulates with a low surface tension, and the surface has to be above that figure for wetting to occur.

Contamination lowers the effective surface energy even when it is invisible. Our coating notes describe the process it feeds.

What Contaminates a Surface

Flux residue, silicone from release agents, skin oils and residue from packaging all reduce adhesion. Silicone is the most damaging because it migrates and a very small amount is enough.

The contamination should be identified before a preparation method is chosen. Our cleanliness notes describe the measurement.

<img src="https://www.gopcba.com/wp-content/uploads/2026/05/smart-home.jpg" alt="Plasma treatment chamber with boards loaded” />

Chemical Preparation

A solvent wipe or an immersion cleaning removes what it can dissolve, and it can also spread a contaminant over a larger area if the wipe is reused. The chemistry has to match the residue.

Aqueous cleaning reaches under components and requires drying afterwards. Our cleaning notes describe the machine selection.

Plasma Treatment

Plasma removes organic contamination and activates the surface, raising its energy. It reaches under components and into shadowed areas where a wipe cannot, which is why it is used before coating on dense assemblies.

The effect decays with time and with exposure to air, so the coating should follow within a defined window. Our floor control notes describe the handling that goes with it.

Dyne Test and Contact Angle

A dyne test applies a series of liquids of known surface tension and records the highest that wets the surface. A contact angle measurement gives the same information more precisely.

The test is taken on a witness piece from the same batch. Our coating inspection notes describe the checks that follow.

Time Between Preparation and Coating

Every preparation decays. The interval between the last preparation step and the coating application should be stated, and the assembly stored in a way that does not recontaminate it.

Our storage notes describe the handling discipline that applies.

Verification

The verification is a dyne test or contact angle measurement on a witness piece, a recorded interval between preparation and coating, and an adhesion check on a sample after cure.

Our quality notes describe how the records are kept.

Process Control and Verification

On a design of this kind, surface energy is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.

Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch. Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.

Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.

A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.

Process Control and Verification

On a design of this kind, surface energy is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.

Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.

Process Control and Verification

On a design of this kind, surface energy is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.

Process Control and Verification

On a design of this kind, surface energy is the item that decides how the rest of the board is arranged. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.

A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.

Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.

FAQ

Does a no clean flux need removal before coating? Often yes. No clean describes a residue that is acceptable uncoated, and it does not describe a surface that a coating will bond to.

Is plasma always necessary? No. It is used where the geometry is dense or the contamination is not removable by other means.

What does gopcb provide before coating? We provide a contamination source identified before a preparation method is chosen, plasma treatment followed by coating inside a defined window, a dyne test or contact angle measured on a witness piece, and an adhesion check on a cured sample.