An integral part of electronics manufacturing is cleaning, which aims to remove potentially harmful contaminants during PCB manufacture. Contaminants may include flux, solder and adhesive residues, and general contaminants such as dust and debris from other manufacturing processes.
The cleaning process improves product lifetime by ensuring good surface resistance and by preventing current leakage leading to PCB failure. In order to achieve good insulation resistance and ensure adequate adhesion of conformal coatings and potting and encapsulation resins, the cleanliness of the electronic assemblies is essential.
Cleaning is required at various stages of electronics manufacturing including prior to stencilling and soldering in order to remove contaminants from previous production stages, after stencilling to remove excess adhesive and after soldering to remove corrosive flux residues or any excess solder paste.
There are also cleaning stages required for the removal of coatings and adhesives when re-work is necessary for the cleaning of actual components and for maintenance of the production line.
Though several manufacturers in the electronics industry are turning to ‘no clean’ processes, where cleaning is not required after soldering, these techniques still leave residues such as rosin and activator, which could cause issues with adhesion and possibly affect the performance of the protecting media applied.
Even with advances in new technologies such as ‘no clean’ fluxes, cleaning is still an essential multi-stage process within the electronics industry.
Given the current concerns and compliance requirements regarding the environment, many electronics manufacturers are moving away from traditional solvent cleaners that use ozone depleting chemicals or contain high VOC content, and replacing them with safer alternatives.
Although many solvent cleaners allow a convenient single stage process, water-based cleaners have several advantages including non-flammable properties, low odour, low/ non-VOC content and very low toxicity.
Be it an ultrasonic, spray under immersion or dishwasher type application, it is important to identify the correct water-based cleaner for the specific job. Water-based cleaners utilise surfactant technology to assist the removal of contaminants from a PCB by reducing the interfacial tensions and suspending or emulsifying them in solution.
Alternatively, water-based flux removers work by saponification, neutralising the flux acids.
The only major disadvantage of water-based cleaners is that they require multiple stages to complete the cleaning process, including a two-stage rinse process and a final drying stage.
A newer type of surfactant-free water based cleaner based on glycols, combines the advantages of water based and solvent based cleaners with minimal rinsing requirement.
Safewash Total (SWAT) offered by Electrolube Ltd is an advanced water-based cleaning technology that is versatile in use, removes multiple contaminants and is also environment-friendly.
Key benefits of Safewash Total water-based cleaners:
- Suitable for a wide range of different equipment and processing types
- Removes a vast array of contaminants
- Suitable for lead-free and no-clean flux, paste and adhesive residues as well as removal of general contaminants such as grease and dust
- Supplied in a concentrate form for use at a range of concentrations depending on the application method
- Contains a corrosion inhibitor enabling safe use on sensitive metals such as copper, silver and aluminium
Electronics can be checked after cleaning for level of contamination of two types of residues, ionic and non-ionic using a number of methods.
Non-ionic residues such as rosin, oils and grease are non-conductive and are usually organic species that remain after board fabrication or assembly, causing problems with their insulation properties. Typical problems include poor adhesion of solder mask, conformal coating and potting compounds as well as encapsulation of ionic contaminants and foreign debris.
Test methods for identifying non-ionic residues include visual examination under magnification alongside analytical methods such as Fourier Transform Infrared Spectroscopy (FTIR).
Ionic contaminants are typically flux residues or harmful materials left behind after soldering, degrading the reliability of electronic components and assemblies by contributing to current leakage between the circuitry, causing corrosion and promoting dendrite growth.
Between the two types, ionic contamination accounts for the larger proportion of failures and can be determined by measuring Resistivity of Solvent Extract (ROSE), also known as Solvent Extract Conductivity (SEC). The industry standard, IPC-TM-650, employs a solution of isopropanol and deionised water to extract the contaminants whilst the meter measures the change in conductivity.
In addition to this test, two further methods, Surface Insulation Resistance (SIR) and Ion Chromatography (IC) can also be utilised to provide valuable data.
The Electrolube Safewash range is a highly effective family of aqueous cleaning products currently in use by major manufacturers in a wide variety of cleaning machines. Cleaning to both military and commercial standards at minimal financial and environmental cost, Safewash Total ensures superior cleaning performance and process flexibility while meeting the environmental goals of modern electronics manufacturers.
Electrolube is a division of the HK Wentworth Group and global manufacturer of electro‐chemicals.