High Voltage Subsystems
Manufacturer of Insulating Gloves
Switches to Vertrel® for High-Voltage Applications
Because of superior materials compatibility and dielectric properties, Vertrel® XF was selected by a manufacturer of insulating sleeves and gloves for the quality assurance function in high voltage product testing.
When technicians and linemen work around high voltages, it is crucial that they be completely insulated from the dangerous circuits upon which they are working. Importantly, the insulation must be prefect because even an invisible flaw in an insulating sleeve may be sufficient to serve as a path for a catastrophic accident.
One company which makes insulating sleeves and gloves needed to change their solvent in their sleeve testing equipment. The test involves submerging the sleeves in an insulating bath of solvent, running an electrical current through the materials and measuring any leakage, which would indicate a flaw in the sleeve. Until recently, CFC-113 was used for this critical task. Importantly, the plastic components must remain unaffected by the solvent.
Vertrel® XF showed superior performance when compared to CFC-113 and other solvent alternatives. During tests, the fluid held AC voltages in excess of 40,000 volts during testing of a sleeve at an immersion depth of 5.08 cm (2 in) with no flashover through the fluid. Based on these tests, DuPont recommends a minimum immersion depth of 7.62 cm (3 in) in commercial testing.
Other observations made during the testing included: no hang-up of water globules on the rubber, eliminating the need to time-delay the test or pre-coat the sleeves with vegetable oil. Also, there was no observed effect on the rubber sleeves after repeated exposures to the solvent.
Tesing showed most elastomers are compatible with Vertrel® XF. Table 1, below, summarizes test results on short-term exposures of unstressed elastomers. Compatibility was defined as a weight change of less than one percent after immersion for 15 minutes at room temperature.
It has been observed that some elastomers will swell upon exposure to the solvent and will, in most cases, shrink back to within a few percent of original size after air drying. Swell, shrinkage, and extractables are strongly affected by the compounding agents, plasticizers, and curing used in the manufacture of plastics and elastomers. Therefore, thorough testing prior to wide-scale deployment is particularly important in this application.
Additional long-term compatibility data simulating exposure of the most common components and materials is available from DuPont upon request.
Table 1 – Elastomer Compatibility Test Results on Insulating Sleeves
Compatible: Buna N, NBR, Nitrile Buna S, SBR, GRS, Butyl Rubber, IIR, Chlorosulfonated PE, EPM, EPDM, Nordel®, Polysulfide, Natural Rubber, Isoprene, Neoprene, Polyurethane
Incompatible: Viton® B, Silicone
Notes: Material composition varies depending upon compounding agents, plasticizers, processing, etc. Specific materials should be tested for compatibility with solvent.
Test Procedure: Immersion,15 Minutes at Room Temperature, weigh and measure.
About the Solvent
Vertrel® XF is a proprietary hydrofluorocarbon fluid with zero ozone depletion and low global warming potential. Nonconductive, it is ideally suited for use in high voltage applications, particularly those in which the materials of construction may be vulnerable to stronger solvents. Vertrel® XF can replace chlorofluorocarbon (CFC-113 or Freon® TF) and the perfluorocarbon fluids (PFC-5052) currently used in this application.
Vertrel® XF is a clear, colorless liquid which dries very quickly with very little aroma. Unique physical properties include a higher boiling point and lower surface tension when compared to CFC-113. This, combined with high dielectric strength, nonflammability, chemical and thermal stability, low toxicity, and ease of recovery by distillation and filtration make Vertrel® XF ideal for this application.
Vertrel® for Defluxing
PCB Makers Choose Vertrel®
XMS Over Co-Solvent Defluxing
A California-based manufacturer of high-power radio frequency (RF) power amplifier systems for application-specific and scientific, medical, and wireless applications chose Vertrel® XMS for defluxing applications because it is compatible with the components, it avoided problems with water cleaning, and lowered their total cost-per-part-cleaned.
American Microwave Technology, Inc. (AMT) is a Brea, California based manufacturer of high-power radio frequency (RF) power amplifier systems for application-specific and scientific, medical, andwireless applications. Its customers are original equipment manufacturers worldwide. Due to the critical nature of the components and the high-tech applications, extreme cleanliness of all the electronic subassemblies is essential.
Circuit board assemblies containing RMA flux must be cleaned as part of their manufacturing process. Any flux residue that is left on the circuit board assemblies can eventually result in failures. The chip capacitors are especially vulnerable. Due to the high power involved in the application of these units, heat can build up in areas where flux residue remains. In the case of a chip capacitor, the flux can cause the capacitor to crack.
AMT had been using a co-solvent process in a Detrex AVD 212 vapor degreaser. They were using Solvating Agent #24 with PFC 5060 from 3M Corp. as the rinsing agent. The relative amounts were 30%/70% respectively on a weight basis.
Although the cleaning performance of this system was satisfactory (and an improvement over the previously used 1,1,1-trichloroethane system), there were concerns about the excessive consumption of the rinsing agent. The odor of the solvating agent was a secondary issue. Additionally, there was concern that the solvating agent was getting trapped under components and not easily rinsed out. The circuit boards had to be oriented very carefully to ensure that pockets that could trap solvent were eliminated. Fluid entrapment also was a concerned under the Teflon® sleeving used on custom-designed subassemblies. Lastly, another concern with the co-solvent system was that wire assemblies that are attached to some of the boards were not being cleaned effectively.
Alternative Chemistry Solution
In an effort to eliminate some of the concerns with the co-solvent system, AMT began to investigate alternative chemistries. They chose to evalutate DuPont’s Vertrel® cleaning agents because these products offered many advantages over the co-solvent system. Tests were conducted at the DuPont Applications Laboratory in Wilmington, DE. Both Vertrel® SMT and Vertrel® XMS were tested on circuit board assemblies.
The test was more stringent than typical production because the flux had been allowed to age on the boards for approximately nine days. Both products performed significantly better than the existing co-solvent process, with Vertrel® XMS showing a slight advantage.
The boards were inspected under high magnification for the presence of flux residue. There was no residue and no fluid entrapment under the Teflon® sleeving used on customdesigned subassemblies, which had been a recurring problem in the existing system.
The swtich to Vertrel® solvents was fast and easy because the vapor degreaser did not need to be modified to switch from the co-solvent process to the solvent process; just a few thermostats needed to be adjusted.