To protect PCBAs from damaging outside influences, they are coated with a thin layer of casting
resin or protective finish during the conformal coating process. In addition to sealing the entire
circuit board, it is possible to pot only sections or individual components on the substrate.
Different methods ranging from "glob top" to "dam and fill" and "flip chip underfill" have been
developed for this purpose.
Things would not be the same today without them. The PCBA (or circuit board) is now the most
frequently used carrier and connecting component for electronic components. There are
practically no limits to its use. In addition to computers, cars and airplanes, PCBs are also used
in household appliances and communication devices, in security electronics and medical devices.
For example, to ensure that airbags deploy reliably and on-board computers in airplanes operate
correctly, the intricate electronics on the PCB must be permanently protected against moisture,
dirt, impact, chemicals and other damaging influences. This is just one of the tasks provided by
potting. Different methods have been developed based on the particular electronic components
(sensors, processors, etc.) to be potted or the potting function(s) required.
Conformal coating
Conformal coating is basically the application of special coatings or potting compounds on the
PCB in order to protect sensitive electronics. Depending on the application, materials can be
applied manually by brush painting or spraying them on. However, due to their high precision
and reproducibility, users are more frequently opting for automated or robot-controlled
application using suitable metering heads.
Easier processing through correct heating
In many cases the viscosity of a dispensing material decreases as its temperature rises. In addition
to faster and easier processing, air bubbles in the material rise faster, rendering any required
evacuation easier. However, keep in mind that filled media tend to settle faster in the form of
sediment in this case. To achieve a continuous and constant temperature, the complete
dispensing process, including storage tanks, material feed lines, pumps and dispensers, etc.,
should be heated. Caution is advised in the case of potting compounds that cure when heated.
Performing a series of experiments with such potting media is recommended before using them
in production.
Dam and fill / frame and fill
Dam and fill is a selective process that enables potting of individual areas on the PCB without
affecting the surrounding surfaces and components. This process, also known as "frame and fill",
uses two potting compounds of varying viscosity. A dam or frame made of high viscosity material
is first dispensed around the section of the board to be protected. The resulting cavity is then
filled with a liquid casting resin until the particular structures are completely covered. The dam
and fill process is also used for optical bonding: In this case, the first step is to dispense a dam on
the substrate to form a gap between the cover glass and display or touchscreen. The dam is then
filled with an optically clear adhesive. In addition to improved heat dissipation and increased
stability, this process also provides significantly better display readability.
Glob top
Another option for protecting selected sensitive areas on the PCB is the "glob top" process. The
only difference between this and the dam and fill process is the potting compound. In this
process, the viscous casting resin is dispensed on a semiconductor chip until it fully encapsulates
the chip and its wire bonding contacts. The potting compound used for this process is not allowed
to flow so easily as to contaminate adjacent components or to coat areas of the PCB that need
to remain open. This must be taken into consideration when choosing the casting resin and
determining the quantity of potting compound required.
Flit chip underfill
Flip chip underfill is a process that was developed specifically for the mechanical stabilization of
flip chips. To reduce stress or deformation between the substrate and flip chip, the thin gap
resulting from the connection is filled with a low-viscosity material, which is called an underfill.
After the material is applied, capillary action helps draw the underfill around the chip into the
narrow gap until it is completely filled with casting resin.
Efficient thermal management for PCB
In addition to conformal coating applications, thermal management applications for PCBs are
also important. Due to their higher performance compared to pads or films, users in this case
are increasingly choosing liquid thermal interface materials.
