According to GfKORR Guidelines
PROTECTIVE COATINGS for ELECTRONIC ASSEMBLIES
SELECTION | APPLICATION | REQUIREMENTS | RECOMMENDATIONS
With our regular posts on Linkedin we inform you about the most important topics about protective coating of electronic assemblies.
The useful tips and information are in accordance with the guideline „APPLICATION AND UTILIZATION OF PROTECTIVE COATINGS FOR ELECTRONIC ASSEMBLIES – Selection, fields of application, requirements and application recommendations“ provided by the GfKORR working party “Corrosion protection in electronics and microcircuitry”.
On this website we provide further details to you.
INFLUCENCE OF THE ASSEMBLY ON THE PROTECTIVE COATING
Not only the coating material itself has an influence on the protective coating. Also the assembly is influencing the coating result.
The base materials used to manufacture the printed circuit board play a significant role in determining the electrical, mechanical and thermal properties and, last but not least, the expected costs of the assembly to be manufactured. The selection of the right base material is therefore essential.
COMPONENT AN CIRCUIT BOARD LAYOUT
On the circuit board, the distances between voltage and current and the insulators between them determine the sensitivity. The design and requirement of areas which need to be coated are based on these conditions.
Since the solder mask remains on the PCB, it must also fulfill its insulating and protective function during the entire lifetime of an electrical assembly. Therefore, solder resist masks have to meet the same high requirements as base materials and components.
SOLDERING MATERIALS AND SOLDERING PROCESS
A soldering process with not proper set parameters can leave large and uneven quantities of flux on the PCB. Moreover, a not proper flow of the liquid tin on the PCB will also leave more residues, which have a direct influence on the electrochemical stability and adhesion of protective coatings.
A protective coating can only fulfill the requirements and achieve full chemical and physical properties after full cure. For this reason, it is important to check the drying and curing parameters for each type of protective coating and assembly, which needs to be coated.
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KEEPING AREAS CLEAR AND EXPOSING AREAS
Some parts of electrical assemblies must remain uncoated, e.g. SMD connectors, THT connectors or
structures that are damaged by coating. In special cases, it might be required to remove the coating.
INFLUENCE SOLDERING MATERIALS & PROCESS
A soldering process without proper set parameters can leave uneven quantities of flux on the PCBA. Moreover, residues from the soldering process can be critical in terms of electrochemical stability and adhesion. Solder material and process have to fit together to reach reliable solder results.
SUBSTRATE AND PRETREATMENT
Prior to applying the protective coating on the pcb, the surface needs to fulfill a certain cleanliness level. Several questions like „How to measure the cleanliness of the pcb surface?“, „How clean is clean enough for my application?“, „Do I have to clean?“ and „How to implement a suitable cleaning process?“ have to be answered.
Scroll down to learn more about requirements & decisions for the cleaning of assemblies, purity requirements and the measurement, detection and analysis of ionic impurities.
REQUIREMENTS & DECISION FOR THE CLEANING OF ASSEMBLIES PRIOR TO CONFORMAL COATING
Traditionally, the result of the cleaning processes is optically evaluated according to IPC-A-610D1. However, mould release agents, grease layers or many fluxes leave behind visually invisible thin residue films depending on the process. Even unsuitable cleaning processes can leave behind invisible adsorption films. These residues impair the possible protective coating and the adhesion of protective coating compounds.
This therefore requires the definition of function-oriented evaluation criteria to characterize the result for cleaning prior to protective coating. In addition to the improved evaluation of process reliability, which can be documented in accordance with DIN ISO 9001:2008 2015, such evaluation criteria also enable more efficient cost optimization of the cleaning process, since quantifiable safety and imperfections of the cleaning process are now visible.
Learn more about the contaminants and their effect in our graphic.