Depending on the environment where the electronic PCB are integrated (humidity, vibrations, salt spray, high temperature, etc.), several solutions are possible:
2 components epoxy resin
2 components polyurethane resin
UV curing glue
RTV silicones cure with the moisture of the air and provide excellent mechanical protection due to their flexibility.
Often used to maintain electronic capacitors, RTV silicone adhesives absorb potential shocks and vibrations.
When no movement of the components is tolerated, two-component epoxy or polyurethane solutions are often used. These glues are generally more rigid and prevent any movement of the components. A glob top can even sometimes be used to completely protect some sensitive components or even the entire electronic system against all external aggressions (chemical aggression, water penetration, abrasions, hacking, etc.). These solutions can be applied manually using two-component cartridges and a static mixer to mix the resin with its hardener, or more industrially using a in line machines.
Nevertheless, more and more gluing are made with UV curable glues. These solutions allow bonding up to 5mm thick with a drying time of a few seconds under UV lamps. These UV glues have the advantage of being available in different ways: fluid to very viscous, flexible to very rigid, with or without tracer…
The main advantage of UV glues is that they reduce the size of production lines and reduce production time due to their very quick drying time. The application of the glue can be done at the same time as the deposit of the conformal coating, and this with a single passage in the UV oven.
It is even possible to:
Glue components in one side of the PCB
Cure it with a UV lamp
Flip the PCB
Put the PCB on the other side
Put the PCB in a reflow oven to solder the top & bottom side at the same time.