5/30/01/ AC 43-206 FIGURE 4-1. NFPA 704 WARNING SYSTEM LABEL
HEALTH HAZARD FIRE HAZARD 4 - Deadly Flash Points 3 - Extreme 4 - Below 73°F danger 3 - Below 100°F 2 - Hazardous 2 - Below 200°F 1 - Slightly 1 - Above 200°F hazardous 0 - Will not burn 0 - Normal material
REACTIVITY SPECIFIC 4 - May detonate HAZARD 3 - Shock and heat may detonate Oxidizer OXY 2 - Violent chemical Acid ACID change Alkali ALK 1 - Unstable if Corrosive COR heated Use NO WATER 0 - Stable
404. AVIONICS CLEANING EQUIPMENT.
a. The following paragraphs identify the different types of avionics cleaning equipment and list their uses and specific restrictions for those pieces of equipment. Table 4-2 lists the recommended cleaning process versus the type of avionics equipment.
NOTE: Avionics technicians should refer to the appropriate equipment service manual for specific operating instructions. Ultrasonic cleaning of printed circuit boards (PCB) is generally not authorized due to the difficulty in determining which component on the board will be susceptible to damage.
CAUTION: Miniature and microminiature PCBs may be susceptible to damage from the ultrasonic frequency, power level, or both.
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b. Cleaning Booth, Water-Based Solvent Spray. The water-based solvent spray booth is used for the removal of dirt, dust, salt spray deposits, and loose corrosion deposits. The cleaning action is accomplished by a detergent and spray system.
TABLE 4-2. RECOMMENDED CLEANING PROCESS VERSUS TYPE OF AVIONICS
EQUIPMENT Type of Equipment Aqueous Ultrasonic Solvent Ultrasonic Water-based Spray Booth Abrasive Tool Mini- Abrasive Hand Clean Housings/covers X X X X X X Chassis X X X X X X Racks/mounts X X X X X X Control boxes X X(1) X X X Instruments X(1) X Light assemblies X X X X(1) X X Wave guides X X X X X X Servos/synchros X(1) X Antenna, blade X X X X X Antenna, dome X(1) X(1) X X(1) X X Antennas, radar X X(1) X X Motors X X(1) X X(1) X X Generators X X(1) X X(1) X X Batteries X Circuit breaker panels X X X X X Gyroscopes X(1) X(1) X Plugs, connectors X X X High-density connectors X X Edge connectors X X X Coaxial connectors X X X Printed circuit boards X X Note: (1) External use only
(1) The spray equipment provides an air pressure powered spray of a detergent/water solution through a handheld spray gun. The water used can be either filtered or tap water. The equipment can also deliver rinse water or a drying jet of air through the gun.
(2) The spray booth may provide for a turntable which allows 360-degree rotation of the avionics equipment being cleaned or rinsed.
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(3) The spray booth operation may be used as a precleaner prior to placing the component in another cleaning process.
(4) The spray booth operation may be used to rinse components after other cleaning processes.
NOTE: Increasing the proportion of detergent in the cleaning solution does not necessarily increase the cleaning power of the detergent. This action can, in some cases, reduce cleaning effectiveness and cause corrosion.
(5) The preferred detergent for the water-based solvent spray booth should conform to MIL-SPEC MIL-D-16791, listed in Appendix 1. The detergent solution should be mixed in accordance with the manufacturer’s instructions or one ounce per gallon of water.
(6) Sealed bearings, synchro and servo bearings, instrument bearings, and similar devices with permanently lubricated (sealed) bearings can experience cleaning solution intrusion and the removal of the lubricant. These components could be rendered useless unless the processing procedures protect those components from degeneration or the lubricant is replaced.
(7) Sealed components (other than hermetically sealed) can trap the detergent and water solution. This may cause drying problems. In each case, the sealed component should be opened and inspected for trapped detergent and water solution.
c. Aqueous Ultrasonic Cleaner. The aqueous ultrasonic cleaner is used for the removal of dirt, dust, salt spray deposits, and loose corrosion deposits. The cleaning action is accomplished by the ultrasonic scrubbing action of the detergent and water solution.
(1) The maximum operating temperature should not exceed 130 °F (54 °C). The maximum operating frequency used should be 20 kilohertz (kHz).
(2) Presoaking avionics equipment and components prior to the ultrasonic function is an additional function of this equipment.
(3) The preferred detergent for the aqueous ultrasonic cleaner conforms to MIL-SPEC MIL-D-16791.
(4) Paper capacitors and paper bound components disintegrate in the detergent and water solution.
(5) Sealed bearings, synchro and servo bearings, instrument bearings, and similar devices should be treated per subparagraph 404b(6).
(6) Sealed components (other than hermetically sealed) should be treated per subparagraph 404b(7).
(7) Thin metal foil types of gummed labels can loosen and separate.
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d. Solvent Ultrasonic Cleaner. The solvent ultrasonic cleaner is used to remove light to heavy oil, grease, and hydraulic fluid contamination by ultrasonic scrubbing in a solvent solution.
(1) Use only an approved solvent in the solvent ultrasonic cleaner. The maximum operating temperature should be the solvent’s boiling point. The maximum operating frequency used should be 40 kHz.
(2) Solvent degreasing, solvent vapor rinsing, and solvent vapor drying are additional functions of the solvent ultrasonic cleaner. Solvent degreasing is performed by solvent ultrasonic action in the degreaser tank. Solvent vapor rinsing (part of the degreasing function) is performed by a solvent vapor cloud. The solvent vapor cloud is created by a cooling coil placed near the top of the degreaser tank. Solvent vapor drying is also performed by the solvent vapor cloud.
(3) The solvent ultrasonic cleaner normally has a solvent degreaser tank. The solvent vapor rinse and solvent vapor drying function do not use the ultrasonic frequency function.
Therefore, they may be used to rinse and dry PCBs.
(4) Some acrylics may be susceptible to damage from the solvents used in solvent ultrasonic cleaners. Coaxial connector gaskets and other neoprene rubber components are susceptible to damage by some solvents. Refer to the manufacturer’s instructions or use another non-solvent cleaning process. See Table 4-3 for other restrictions.
(5) Sealed bearings, synchro and servo bearings, instrument bearings, and similar devices with permanently lubricated bearings should be treated as described in subparagraph 404b(6).
(6) Sealed components (other than hermetically sealed) should be treated as described in subparagraph 404b(7). The sealed component should be opened and inspected for trapped solvent.
e. Abrasive Cleaning Tools. Abrasive cleaning tools such as portable mini-abrasive units and blast cleaning cabinets are used to remove corrosion and corrosive products.
(1) The abrasive blast medium used in abrasive cleaning tools can easily be trapped in miniature and micro miniature female edge connectors. When working on components where these connectors are installed, the connectors should be sealed with pressure-sensitive tape. Upon completion of the cleaning process, ensure the tape is removed.
(2) Delicate metal surfaces, such as metal plating, are susceptible to damage from indiscriminate, unauthorized use of abrasive cleaning tools. Only properly trained personnel are authorized to use abrasive cleaning tools on avionics equipment.
(3) Some miniature/micro miniature PCBs contain electrostatic discharge (ESD)-sensitive devices (Chapter 9). These ESD sensitive devices may be destroyed by the static charge created in the rapid movement of air and abrasive agents in the abrasive cleaning tools.
Therefore, abrasive cleaning tools are not authorized on components where ESD-sensitive devices are installed.
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405. AVIONICS CLEANING PROCEDURES.
a. General. Corrosion products and contamination by other sources previously described in Chapter 2 and this chapter are responsible for numerous problems and failures in avionics equipment. Proper cleaning can prevent many of these problems and is the next logical step after the initial inspection. Cleanliness is very important in maintaining the functional integrity and reliability of the avionics system and components. Corrosion products and contaminants can be either conductive or insulating. As a conductor they may provide undesirable electrical paths, and as an insulator they may interfere with the avionics equipment or systems operation. The following paragraphs contain information and suggested procedures for the cleaning of avionics equipment.
b. Cleaning Method Selection Criteria. The best technique for selecting a cleaning method is to select the mildest cleaning method that will accomplish the task. The selection of the cleaning method is a decision that may be outlined in an OEM’s maintenance manual or made by authorized personnel at the avionics equipment repair station. The decision on the mildest cleaning method should consider the following:
(1) Certain circuit components can be damaged by support equipment and cleaning solutions and solvents;
(2) Type and extent of the corrosion damage or contamination;
(3) Accessibility to the corrosion damage or contamination; and
(4) Type of avionics equipment.
c. Hazards of Cleaning. As previously mentioned, it is a good maintenance practice to use the mildest cleaning method that will ensure the removal of the corrosion or the contamination. It is also important that the correct cleaning solutions and cleaning materials be used to avoid further damaging the avionics equipment. The following items are offered to emphasize some of the hazards that can occur during cleaning of avionics equipment:
(1) Cleaning solvents or other cleaning materials can become trapped in crevices or seams of components or chassis. These trapped cleaning materials could then interfere with the application of protective coatings and result in the initiation of corrosion.
(2) Vigorous or prolonged scrubbing of laminated circuit boards can cause damage to the boards.
(3) Certain cleaning solvents can soften conformal coatings, wire insulation, acrylic panels, and PCBs.
d. When to Clean. The immediate removal of corrosion or contaminants on avionics equipment and the surrounding structure is always a high priority in a good Corrosion Prevention and Control Program (CPCP). Therefore, immediate cleaning should be accomplished on avionics equipment and components if they have been exposed to adverse weather, saltwater
Par 405 Page 55 immersion or spray, fire extinguishing agents, spilled battery electrolytes, other acids, high pH alkaline cleaners, mercury, and corrosion products during component repair.
e. Precleaning Criteria and Cautions.
(1) Disconnect electrical and other power sources (mechanical/hydraulic).
(2) Ensure the work area and equipment are safe for maintenance.
(3) Ensure drain holes are open.
(4) Remove covers and panels for accessibility.
(5) Disassemble where practicable.
(6) Use only authorized materials.
(7) Ensure compatibility of materials prior to use.
(8) Mask and protect accessories or components to prevent intrusion of water, solvents, and cleaning solutions.
f. Cleaning and Drying Restrictions. Certain circuit components create potential problems during cleaning and drying. These problems can generally be overcome prior to cleaning the equipment by carefully masking those components likely to trap and hold cleaning liquids due to their construction. Table 4-3 lists different components and describes techniques to avoid problems. Mechanical, shock, and heat damage are other types of damage that can occur during cleaning and drying. The following suggestions are provided to avoid trapping water and solvent during cleaning:
(1) Seal small components with pressure-sensitive tape. Ensure tape and any tape residue are removed using an approved solvent prior to drying the component.
(2) Seal large components in static-free plastic bags or other water and vapor-proof barrier material. Place the plastic bag or barrier material around the component and seal with pressure-sensitive tape. Ensure tape and any tape residue are removed using an approved solvent prior to drying the component.
(3) When possible and if authorized, remove subassembly components and clean separately.
Par 405 Page 56 TABLE 4-3. CLEANING AND DRYING RESTRICTIONS Component Problem Solution APC connections (microwave) Shock damage to center conductor Seal and hand clean only Crystal detectors Heat damage from ovens Dry at 130 °F (54 °C) maximum Delay lines Trapped solution in housing Seal or remove Fan motors Trapped solution in housing Seal or remove Gyroscopes Trapped solution in housing Seal Klystron cavity Trapped solution in sockets Remove tube and seal Meters and instrument gauges Trapped solution through open housing Seal Paper capacitors Disintegrate Seal Potentiometers Trapped solution in open housing Seal Printed circuit Trapped solution (when installed) Remove (clean separately) Rotary switches Trapped solution in open housing Seal Sliding attenuators (radio frequency (RF)) Trapped solution in slide housing Seal or remove Sliding cam switches Shock damage to cam only Remove or hand clean Synchros and servos Lubricant removed from bearing Seal or remove Transformers Trapped solution in housing Seal Tunable cavities Trapped solution in cavity area Seal or remove Vacuum tubes Shock damage Remove Variable attenuators (microwave) Trapped solution in housing Seal or remove Wave guide (microwave) Trapped solution in housing (when installed) Seal or remove Wire wrap connections Shock damage Hand clean only
g. Hand Cleaning Methods. Hand methods should be used for cleaning small, delicate, confined surfaces where parts cannot tolerate other cleaning methods. Also, hand cleaning methods should be used when accessories/facilities for other methods are not available. The following list contains some of the equipment that may be utilized for hand cleaning:
(1) Lint-free cloth;
(2) Cheesecloth;
(3) Cotton-tipped applicator;
(4) Acid brush;
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(5) Toothbrush;
(6) Other soft bristle brushes; and
(7) Plastic manual spray bottle.
h. Fingerprint Removal. The salts and oils from human fingerprints are highly corrosive.
The following paragraphs list the material and procedures for their removal:
(1) Apply a mixture of 1 part Isopropyl Alcohol, TT-I-735, or other approved solvent and 1 part distilled water to the affected area with a clean cloth, cheesecloth, acid brush, or toothbrush as appropriate;
WARNING: Do not use a synthetic fiber wiping cloth with Isopropyl Alcohol, TT-I-735, due to its low flash point. A dry fiber wiping cloth will cause a static charge to build up and can result in a fire.
(2) Wipe or scrub affected area until contaminants have been removed;
(3) Remove residue by wiping or blotting with clean cheesecloth or cotton-tipped applicator as required. Inspect area for signs of residue or contaminants;
(4) Discard contaminated cheesecloth or cotton-tipped applicators and solvents in an approved container after cleaning operations to avoid contamination of other components; and
(5) Repeat process as required until all evidence of contamination is removed.
i. Cleaning and Removal of Solder Flux Residue. Solder flux residue is present in all soldering operations. This residue will cause corrosion if an electrolyte is present. Use of an approved cleaning solvent or diluted Isopropyl Alcohol, TT-I-735, is required. These solvents should not damage associated wiring circuit components or laminated circuit board coatings. The presence of soldering flux can be detected by using ultraviolet (UV) light. Under the presence of UV light, traces of solder flux appear as a fluorescent yellow to brownish residue. Clean solder flux residue as follows:
WARNING: Lead contained in solder can rub off onto a person’s fingers from a soldered joint. Lead and lead oxide are toxic and cannot be eliminated from the body. This toxic poison will accumulate in the body. Touching solder followed by smoking or eating is a potential means of ingesting trace amounts of lead. Wash hands thoroughly following any soldering or desoldering operation.
(1) Solder flux residues should be removed from circuit boards and circuit components using the general procedures described in subparagraph 405h. Use a solution of 1 part distilled water to 3 parts Isopropyl Alcohol, TT-I-735, to clean the affected area. After a soldering operation, clean the affected area and one inch around the solder point to ensure complete decontamination.
Par 405 Page 58 CAUTION: Prior to using the UV light for inspection to ensure complete removal of soldering flux residue, examine the piece of equipment for erasable programmable read-only memory (EPROM) components. EPROM have windows that are usually covered with an aluminum foil mask or black tape. Visually examine to ensure the tape or foil has not lifted from the window.
NOTE: UV light from an UV light inspection light source is very intense and can degrade EPROM devices.
(2) Visually inspect circuit boards and circuit components for evidence of soldering flux residue using an UV light source. Repeat cleaning process as required until all evidence of solder flux is removed.
j. Cleaning and Removal of Silicone Lubricant. Remove silicone residue from surfaces coated with silicone lubricant as follows:
(1) Wipe or scrub contaminated surface with a cleaning cloth, cheesecloth, acid brush, or cotton-tipped applicator dampened with an approved solvent or Naphtha, TT-N-95B, Type II, until surface is clean;
(2) While surface is still wet, wipe area dry with clean cheesecloth or cotton-tipped applicator as appropriate; and
(3) Discard contaminated cheesecloth, cotton-tipped applicators, or other cleaning devices, and solvents in an approved container after cleaning operations to avoid contamination of other components.
k. Cleaning and Removal of Bacteria and Fungi. Dust, dirt, and other airborne contaminants are leading contributors to bacterial and fungal (microbial) attack. The best defense against this form of attack is to maintain cleanliness and, where possible, low humidity. Remove fungi and bacteria as follows:
(1) Mask air capacitors, relay contacts, open switches, tunable coils, and other components affected by solvents with pressure-sensitive tape; and
(2) Treat affected areas with materials and instructions described in subparagraph 405h.
l. Cleaning and Removal of Dust. Dust, dirt, grease, and oil should be removed from components as follows: (Figures 4-2 and 4-3 show dirt accumulation in an engine compartment.)
(1) For dust and dirt, apply a solution of 1 part Aircraft Cleaning Compound, MIL-PRF-85570, Type II, to 9 parts of distilled water;
(2) For grease and oil, apply a solution of 1 part Aircraft Cleaning Compound, MIL-PRF-85570, Type II, to 4 parts of distilled water;
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(3) Wipe or scrub affected areas or components with cleaning cloth, cheesecloth, acid brush, toothbrush, or cotton-tipped applicator until surface is clean; and
(4) Rinse affected area or component with fresh water and dry with a clean cloth or cheesecloth.
FIGURE 4-2. ENGINE COMPARTMENT ELECTRICAL CONNECTORS
m. Sur face Preparation. The true cleanliness of bare metal surfaces after a cleaning process is very critical to adhesion of any subsequent coating material. Examples of subsequent coatings include: chemical conversion coating (prepaint), paint system, sealant, dry film lubrication, etc. The method generally used to identify a surface that is clean enough for adhesion of any of the subsequent coatings is called the Water Break Test. Figure 4-4 illustrates a water-break surface. Perform a Water Break Test as follows:
(1) Feather edges of any existing paint finish (if applicable) to ensure a smooth overlapping transition between the old and new paint coating. Feathering can be accomplished using 240-grit or 320-grit aluminum oxide abrasive cloth or a fine or medium grade abrasive mat.
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(2) Clean (lightly scrub) the area with very fine or fine abrasive mat saturated with water. Rinse surface with fresh water. Particular attention should be given to fasteners and other areas where residues may become entrapped.
(3) Visually inspect the part after the last rinse; the surface should be water-break free (see Figure 4-4). A surface showing water breaks (water beading or incomplete wetting) is contaminated, usually with grease or oil (fingerprints, etc.). The contaminated surface will not allow proper adhesion with any subsequent protective coating system (conversion coating, primer, topcoat).
(4) If the surface is not water-break free, clean area with a solution of 1 part Aircraft Cleaning Compound, MIL-PRF-85570, Type II, to 9 parts distilled water. Lightly scrub the area with very fine or fine abrasive mat saturated with cleaning solution. Rinse surface with distilled water. Visually inspect the part after the last rinse. The surface should be water-break free.
FIGURE 4-3. ENGINE COMPARTMENT ELECTRICAL CONNECTORS
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n. Special Considerations. Dust, fingerprints, surface oxides, and other contaminants can undo the protection provided by subsequent protective coatings. Specific avionics equipment and components should be cleaned by procedures addressed for the specific equipment in Chapter 5.
o. Post-Cleaning Procedures.
(1) After completion of the cleaning steps, inspect the affected area for signs of residue, surface film, or water.
(2) If inspection reveals the area is not clean, (residue, surface film), repeat the appropriate cleaning procedures. Water displacement, preservation, and lubrication should follow the cleaning and drying steps for completing the preventive maintenance.
406. DRYING EQUIPMENT AND PROCEDURES.
a. General. Drying time depends on the complexity of the equipment/component being dried. The more complex the individual component, the longer the drying time. Another consideration in drying time is the humidity or moisture content of the air where the drying oven is operated. The higher the moisture content of the ambient air, the longer the drying time.