dielectric coating spary

Thread Starter

Mullins

Joined Dec 31, 2021
179
Hi.
I use this conformal coating to protect the components after rework.
today I thik that I useed a thick layer and I'm scared it will be a problem if the product remain still liquid inside.
Some time ago I use this product and I see spark from one capacitor on the pcb. So I use my fluke dmm to test the conductivity and I saw that the result was 5nS immediately after spraying the product with the probe at 1mm between them.
This is the question:
If the product remain wet in the deep may it give some problem?
Ps.
Anyone know some kind of dielectric gel. it must be liquid and become gel after application.
 

Irving

Joined Jan 30, 2016
4,001
If you cure it fully it will be fine. You must leave it at least 24h or more to cure, preferably at above room temp. in an airdrier/oven to ensure all the solvent has evaporated before using/applying power.
 

ZCochran98

Joined Jul 24, 2018
305
ok but just for knowledge, 5ns/mm is considered dielectric?
That's 200 M\(\Omega\cdot\mathrm{mm}\) (or about \(2\times10^9\,\Omega\cdot\mathrm{cm}\)) which is pretty resistive (more so than FR-4, which is about \(10^8\,\Omega\cdot\mathrm{cm}\)). So it is considered a dielectric.

Edit: what defines a dielectric is not its resistivity/conductivity, precisely, but some other factors. From a physics point-of-view, a dielectric is a material (that is most likely an insulator/non-conductor) that has majority bound charges (i.e.: charges in the material not permitted to move freely from their host atoms). This property makes it insulating, typically, and gives that material a finite dielectric constant (or electrical permittivity), \(\epsilon_r\) (or \(\kappa\) or \(D_k\)), and a few other electrical properties (such as breakdown field, where the bound charges aren't so bound anymore and instead happily conduct through the material. That's what lightning is - the result of dielectric breakdown in air).

Edit 2: there are some dielectrics that have some shocking resistivities, but are still considered as "insulators" or dielectrics because they aren't metals or conductors, by the technical definition. Germanium is one of them (especially doped Germanium), which can have resistivities as low as \(<20\,\Omega\cdot\mathrm{cm}\), but still have a finite, measurable dielectric constant. In fact, many semiconductors have weird properties like that, but still can be considered as dielectrics (for instance, silicon has \(\epsilon_r \approx 11.7\), but its conductivity varies with its boron or phosphorous doping levels,taking it from pure insulator to semiconductor).
 
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