Galden® PFPE is a line of high-performance, inert, fluorinated fluids used as heat transfer and for various high-tech applications in the Electrical & Electronics and Semiconductors markets.
Galden® fluids are low molecular weight Perfluoropolyether (PFPE) having the following general structure:
Galden® PFPE is a line of dielectric fluids with boiling points ranging from 55 °C to 270 °C and a typical operating range from – 70 °C to 270 °C.
Galden® PFPE fluids are high performance, inert fluids characterized by:
Their excellent dielectric properties, high chemical stability combined with their capacity to operate at very low as well as elevated temperatures and in aggressive conditions make them useful in many industrial applications.
Typical industries served by Galden® PFPE fluids are semiconductor manufacturing, electronic testing and cooling, cleaning, carriers for fluorinated lubricants, solar, CPI, batteries, pharmaceutical and food.
The products offered for use in heat transfer applications are called Galden® HT. This is a line of dielectric fluids with boiling points ranging from 55 °C to 270 °C. Galden® PFPE excellent dielectric properties, high chemical stability combined with their capacity to operate at very low as well as elevated temperatures make them the best heat transfer fluids for the aggressive conditions found in many semiconductor processes, electronic, and solar industries.
Non-reactivity, excellent dielectric properties, low toxicity, non-flammability, and non-solvent features make Galden® D electronic fluids suitable for electronic reliability testing including thermal shock and hermetic seal testing.
Thermal shock testing
Thermal shock testing is performed to check the resistance of electronic devices to extreme changes of temperature; often used for automotive and in the military applications. Here are some of the standards often referenced: MIL STD 883 method 1011 or MIL STD 202 method 107. The test is carried out by alternately dipping the devices in liquids maintained at two different temperatures; many applications test devices at 65 °C and 150 °C or higher. Galden® D fluids can be used both for single and dual fluids systems.
Hermetic seal test
Electronic devices must be completely sealed to avoid moisture to penetrate and damage the electrical response of the silicon chip. Here are some of the standards often referenced: MIL STD 883, MIL STD 750 and MIL STD 202. Galden® D fluids being extremely inert and residue-free are currently used as detector and indicator fluids in leak test procedure.
VPS’ principle is to use the latent heat of condensation of Galden® PFPE vapors in order to melt solder paste and hence to obtain reliable metal joints. The narrow molecular weight distribution, as well as the very strong carbon-fluorine bond containing no bromines, and the flexible ether link provide the properties which make Galden® LS/HS ideal for use in VPS.
Galden® SV fluids are low molecular weight perfluoropolyether fluids that have no flash point and are inert, non-toxic, odorless and colorless. They are used for cleaning operations where solvents are:
Galden® PFPE is a line of dielectric fluids with boiling points ranging from 55 °C to 270 °C.
For heat transfer application the working temperature ranges are reported in the graph below and the temperature limits are set as follows:
Operating temperature range
The pour point is the lowest temperature at which a fluid will flow. This property is crucial for fluids that must flow at low temperatures. A commonly used rule of thumb when selecting fluids is to ensure that the pour point is at least 10 °C lower than the lowest anticipated ambient temperature. Galden® HT line of fluids offers a wide range of very low temperatures pour points from – 115 °C to – 66 °C.
|Grade||Pour Point [°C]|
The density of a material is defined as its mass per unit volume. Density at 20 °C for Galden® PFPE grades is the following:
Viscosity is an internal property of a fluid that offers resistance to flow. The viscosity of a liquid usually depends on its temperature. Viscosity generally decreases as the temperature increases and generally increases as the temperature decreases. For many heat transfer applications the lower temperature limit (pumpability limit) is set when the fluid viscosity reaches the value of 20 cP (11 – 12 cst).
Kinematic viscosity vs. temperature
No, Galden® PFPE are not flammable. They don’t have flash, fire or autoignition point.
No, Galden® PFPE are very safe fluids:
Galden® PFPE are stable in thermal conditions above 300 °C. In the presence of oxygen the continuous use temperature of these fluids is somewhat lowered to 290 °C. Up to these temperatures, the decomposition of the fluids is negligible. Galden® PFPE can be stored and handled without specific precautions, do not react with chemicals and refrigerants and does not get oxidized.
Galden® PFPE are stable in thermal conditions above 300 °C. In the presence of oxygen the continuous use temperature of these fluids is somewhat lowered to 290 °C. Up to these temperatures, the decomposition of the fluids is negligible.
No. Galden® PFPE do not corrode metals because they interrupt the electrical circuit that is the base for the corrosion process: the conducting environment for ionic movement is disabled by the high volume resistivity of Galden® PFPE fluids that does not vary over time (the volume resistivity of DI water is at least 107 Ω · cm, and this value tends to reduce over time – DI water extracts metal ions).
|Volume Resistivity (Ω · cm)||> 1015||< 107|
Corrosion in Galden® PFPE heat transfer systems can generally be linked to either a separate water phase or thermal decomposition of the fluid. In order to have a separate water phase the amount of water in the system must be beyond the saturation level of the fluid. The saturation level of water in a Galden® PFPE fluid is usually less than 20 ppm by weight. Water present in the fluid at or below this level has never been linked to corrosion. Water present above this level means a separate water phase. If such water is entrained into contact with metal parts, corrosion can be rapid. Water can enter heat transfer systems in a few different ways: components can be hydrotested and never dried before installation.
Thermal decomposition of the fluid: fluoride ion can be generated any time the fluid is brought above its decomposition temperature and this can lead to corrosion. Thermal degradation for Galden® PFPE start at about 290 – 300 °C. HF can be generated only when the fluid is brought above its decomposition temperature and these conditions are far from the working temperature range. Experience indicates that corrosion resulting from decomposition is very rare and is only observed in systems which have undergone a failure. Examples include: a burned out heater, high voltage discharge in dielectric systems or a burned out electrical component in a direct contact electrical application.
Galden® PFPE fluids are excellent dielectrics. This is the main reason they are used in many applications.
|Dielectric strength||kV at 2.54 mm gap||40|
The saturation level of water in a Galden® PFPE fluid is usually less than 20 ppm by weight.
Galden® PFPE fluids are increasingly used as heat transfer fluids, especially in the tools used in semiconductor manufacturing. They are fluorinated fluids and their excellent dielectric properties, high chemical and thermal stability combined with their capacity to operate at very low as well elevated temperatures make them the best heat transfer fluids for the aggressive conditions used in semiconductor manufacturing.
The compatibility of a fluid with various materials is strongly dependent on the fluid properties.
Surface tension is a measure of the fluid to wet other materials – the lower the surface tension, higher is the wetting power. Galden® PFPE fluids have low surface tension and are capable of wetting almost all the conventional sealing and gasket materials. This allows the fluids to creep out of very small leak paths. The best sealing materials should have low surface energies in order to minimize wetting.
In spite of the excellent compatibility, due to the low surface tension, these fluids could penetrate the elastomers and plastics and cause swelling and/or extraction of plasticizers and fillers. Swelling could have a positive effect on sealing, but the sealing could fail if the joint is opened for maintenance or other purposes. It is recommended that a new seal or gasket material is used if excessive swelling is noticed. The extraction of plasticizers would reduce the elasticity of the seals, gaskets, hoses and tubes. The material could turn rigid and become brittle. This problem could become severe if there is temperature cycling.
Galden® PFPE fluids are excellent dielectric fluids and possess high electrical resistivity. This property that makes these fluids very attractive for their use in semiconductor manufacturing tools that use Rf energy, has one negative effect – potential to build-up of static electricity when these fluids flow on non-conductive materials such as plastics and elastomers. The build-up static electricity, when reaching high values, will discharge into the surroundings with arcing. This could cause pinholes in hoses and tubes causing the fluid to leak.
The build-up and discharge of static electricity depend on many factors such as nature of the material, flow velocity, surrounding humidity etc. and is very difficult to reproduce in the laboratory. One of the properties that determines the dissipation of the built of electrostatic charges is the conductivity of the fluid as well as that of the tube or the hose in which the fluid flows. One would expect a quicker dissipation with the increased conductivity. Conductive hoses and tubes with good grounding have been and are being used in the industry with good success. The conductivity of the fluid could be increased by suitable additives as done with gasoline. However, additives may affect the dielectric properties of the fluid and may be absorbed by filters in the system.
The commonly encountered materials of construction can be classified into elastomers, plastics and metals. Before selecting these materials, it is important to verify if they are recommended for the temperature range of interest. The compatibility of these materials with the fluids depends on the base material and the formulations used in making the seals, gaskets and hoses as well as the operating temperatures and temperature cycling.
The compatibility of the pure materials could be different from that of the seals and gaskets that are formulated with these materials. Different formulated products based on the same base material could have different compatibility. Hence it is very difficult to make general statements about the compatibility. Often compatibility tests have to be performed with the formulated seals and gaskets.
Fluorinated elastomers include Tecnoflon® FKM/FFKM produced by Solvay Specialty Polymers, Viton® produced by DuPont and Fluorosilicones. Fluorinated plastics include Algoflon® PTFE, Hyflon® MFA®, and Hyflon® PFA produced by Solvay Specialty Polymers and Teflon® produced by DuPont. Typically fluorinated products have low surface energies and hence are difficult to wet. They make good seals against Galden® PFPE. However, compatibility of the seals and gaskets made out of these materials with Galden® PFPE a under operating conditions should be confirmed before using them. For example Kalrez® is an expensive, specialty fluorinated material, but its physical compatibility with Galden® PFPE fluids is very poor.
Among the non-fluorinated materials, silicones have the lowest surface energy and hence make leakproof seals and gaskets for the Galden® PFPE. As in the case of fluorinated materials, the compatibility under operating conditions should be confirmed. Hoses and tubes made of other materials such as NBR, BR, EPDM, PB etc. have been successfully used; it is important to confirm that leaching of plasticizers will not be an issue with these hose materials.
The build-up and discharge of static electricity is an important phenomenon that should be controlled in order to avoid pinholes and subsequent fluid losses. Where metal tubes cannot be used, conductive hoses with suitable grounding have been successfully used to eliminate problems related to static electricity build-up. When using these conductive materials, in addition to swelling and changes in the mechanical properties of the materials, leaching of the conductive filler should also be considered. Generally, using carbon fillers increases the conductivity of plastics. Some hoses have a thin layer of carbon deposited on the plastic. The latter have not been found to be very useful due to the breaking down of the carbon layer caused by fluid attrition with time. The carbon so liberated could deposit on undesired parts of the tool.
Galden® HT, if properly used, i.e. far from thermal degradation temperature and in waterfree system, are fully compatible with metals commonly encountered in TCUs or chillers; they do not corrode and do not react with construction materials. Compatibility tests with different metals and at different temperatures have been carried out and no evidence of corrosion or reaction were detected. With reference to AlMgSi alloy and Stainless Steel 1.4404, based on our experience and knowledge we do not expect any adverse reaction.
Test conditions: Compatibility tests have been carried out using pure Galden® PFPE at 200 °C for 500 hrs.
|Stainless Steel 1.4301||Compatible|
|Stainless Steel 1.4404||Compatible|
*test carried out at 90 °C per customer’s request
Once again, the unique properties of these fluids and the unusual conditions under which they operate, make it necessary to pay particular attention to the selection of valves and fittings. Valves with static seals have shown to be very effective in reducing fluid losses due to leakage. Swagelok, a leading manufacturer of valves and fittings has carried out several tests with Galden® PFPE fluids. These tests included higher system pressures, temperature cycling and leak rate measurements. The major reason for fluid leakage is the dynamic seal in a plug valve. This problem could be overcome by the use of ball valves with static flange seals. Silicone seals have shown good performance over a wide range of temperatures.
Fluid leakage due to poor material compatibility and poor choice of seals and gaskets could amount to thousands of dollars as well as to undesired loading of environment. Solvay Specialty Polymers has carried out compatibility tests in their laboratories and also work closely with manufacturers of OEM tools, thermal control units (chillers and heat exchangers) and system components such as pipes, seals & gaskets and valves & fittings.
As a general rule the following tab can be followed:
|AISI 316||PE low density||Butyl rubber|
|Iron||ABS copolymer||Natural rubber|
The compatibility of the pure materials (i.e. elastomers) could be different from that of the seals and gaskets that are formulated with these materials. Different formulated products based on the same base material could have different compatibility. Hence it is very difficult to make general statements about the compatibility. Often compatibility tests have to be performed with the formulated seals and gaskets.
The following plastics (not formulated) were unchanged after immersion in Galden® PFPE for 1,000 hrs at 70 °C:
We suggest selecting a HT fluid according two main parameters:
Viscosity at the lowest operating temperature
Vapor pressure at the highest operating temperature
Two factors have been introduced in order to evaluate the heat transfer properties of a fluid flowing in a system without knowing the geometry of it.
Heat Transfer Performance can be predicted by means of:
Both factors are function of fluid properties and are subjected to change with temperature. HTf and Fρ can be plotted vs. temperature and used for comparing fluids (given the same geometry of TCU and flow conditions).
Heat Transfer Factor (HTf): HTf = 0.023 · k 0.67 · (r ·cp) 0.33 · n – 0.47
k = Thermal conductivity
r = Density
cp = Specific heat
n = Kinematic viscosity
HTf compares the capacity of fluid to add or remove heat under fully developed turbulent flow conditions (Re > 10,000) for a given geometry.
Higher the HTf, better is the heat transfer efficiency.
Pressure Drop Factor (Fρ): Fρ = 0.092 · ρ · ν 0.2
ρ = Density
ν = Kinematic viscosity
A lower Fρ relates to reduced frictional losses, given the same fluid velocity and tube geometry.
Higher the Fρ, the higher is the pumping power required.
For Galden® PFPE grades, a general recommendation is not to install a heater watt density higher than 4 ÷ 5 W/cm2, in order to avoid instability in heater surface temperature for low flow units (i.e. fluid reservoir in the TCU). Having the heater section where fluid flow is present near the outlet of the pump, it will allow higher watt density heaters to be used. The critical breakdown is ~ 14 W/cm2. We recommend 4 W/cm2. The decision to go beyond this level should be made by the customer.
Galden® LS/HS fluids are specifically designed for vapor phase soldering process. A strict control of the molecular weight distribution and of the vapors temperature is performed by measuring respectively:
The above characteristics are always included in the material specifications:
|Distillation range [°C]||196–212||212–223||222—235||237–250||256–273|
|Boiling temperature TRV [°C]||194–200||212–218||227–233||237–243||260–265|
The sharp molecular weight distribution eliminates the preferential evaporation of low boiling components during VPS process. This phenomenon leads to higher losses of the fluids as well as a shift towards higher vapor temperature with time ► undesired boiling point drift.
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid. Boiling temperature for each fluid is determined according test method ASTM D1120. TRL means Temperature Reflux Liquid and it is a value worth for HT Fluids. TRV means Temperature Reflux Vapor and it is a value worth for HS and LS Fluids.
Even at room temperature Galden® PFPE fluids have a vapor pressure value higher than 0 Torr, so they release vapors even if at negligible rate, depending by grade. In order to detect fluid leaks a halogen leak detector can be used; these are available through most commercial refrigeration supply centers.
Galden® PFPE fluids are NSF approved all with the related intended use described below.
Yes. Galden® PFPE fluids satisfy MIL requirements. Hermetic seal testing is performed to check hermetic devices.
Leak test procedure is performed according to:
|MIL Standards recommendations for testing fluid properties|
|Appearance||Clear and colorless|
|Density at 25 °C||> 1.6 gm/cm3|
|Dielectric strength at 2.54 mm||> 30 kV|
|Viscosity profile||According the equipment manufacturer|
|Residue||< 50 ppm|
|Composition*||NO chlorine and NO hydrogen|
*It is not a restriction; the use of products having chlorine or hydrogen is allowed
The real shelf life of Galden® PFPE as far as the chemical stability is concerned is over 20 years based on our experience. Within this time frame the above products, if stored under normal condition in original sealed containers, maintain their chemical-physical properties unchanged.