Vacuum Coating Thickness Measurement Methods and Equipment

Methods for Measuring Vacuum Coating Thickness

Methods for measuring vacuum coating thickness

Roll-to-roll vacuum coating technology emerged in the late 1970s and has since developed into a widely used process. It coats flexible rolls of material—such as plastic film or metal foil—directly under vacuum, enabling high production efficiency.

1. Types of roll-to-roll vacuum coating

Roll-to-roll vacuum coating can be divided into two main categories: thermal evaporation and magnetron sputtering. Heated evaporation equipment can be further classified as aluminum-wire-fed evaporation, electron-beam heating, and crucible induction-heating evaporation systems.

2. Methods for measuring vacuum-deposited layer thickness

Coating thickness is an important quality indicator closely related to the performance of laminated packaging products. For vacuum-metallized aluminum film, the coating can be described by the actual thickness of the aluminum layer, the optical density of the film, or its surface resistance.

Some factories stack two layers of metallized film and look at them against a 40 W fluorescent lamp, judging the coating acceptable if the light cannot be seen through the stack. This method is strongly affected by visual perception and can vary from person to person. More reliable aluminum-coating measurements generally use one of the following methods:

1. Contact surface profiling with a step profilometer (alpha-step), in angstroms (Å)

A good step profilometer may offer measurement resolution down to 1 Å and repeatability of about 5 Å. However, these instruments can be expensive and inconvenient to use. Measuring the aluminum layer on a plastic film with a contact profilometer can also be difficult, so this method may not be practical for many film manufacturers and users.

2. Non-contact optical-density measurement with a film-thickness tester

The coating can be evaluated using optical density (OD) or light transmittance (T%). A thicker aluminum layer generally has a higher OD and a lower transmittance. When T is expressed as a percentage, the relationship is:

OD = log10(100 / T%)

For example, lower transmittance corresponds to higher optical density. This non-contact approach is useful for assessing very thin metallized layers where ordinary thickness gauges may not be suitable.

3. In-line coating-thickness measurement for vacuum-coating equipment

A roll-to-roll coating line should be equipped with an in-line inspection system. The measured coating data—often represented by OD—can be sent to the main PLC controller and compared with the target coating value. The control system can then adjust the evaporator heating power or the roll-to-roll speed to help bring the coating thickness back toward the setpoint.

For an in-line measurement system on roll-to-roll vacuum-coating equipment, Fulcrum Technology recommends the LS152 in-line vacuum-coating thickness gauge. Its OD and transmittance readings can support continuous process monitoring and help manufacturers manage coating consistency on the production line.