ASI 388 Electronic Grade RTV Silicone, Clear, 2.8 oz Squeeze Tube

ASI 388 Electronic Grade RTV Silicone is a one-part, moisture-curing silicone from American Sealants Inc. (ASI) made for bonding, sealing, encapsulating and protecting electronic parts. It cures by a neutral (oxime) chemistry instead of releasing acetic acid, which is why ASI describes it as non-corrosive and electronic grade. This clear 2.8 oz squeeze tube is the bench size: enough for repairs, prototypes and small batches, applied by hand.

Key features

• Neutral-cure (oxime) RTV silicone; one component, no mixing
• Electrical insulator: 500 V/mil dielectric strength (ASTM D149) and a volume resistivity of 3 × 10¹⁵ (ASTM D257), per ASI
• Service temperature -70°F to 400°F, with intermittent exposure up to 450°F
• UL Recognized (File No. E209770) and meets MIL 46106B Type 1
• Skins in about 20 minutes and cures in about 24 hours per 1/8″ bead at 70°F and 50% RH; non-slump on vertical surfaces
• Cures to a clear (translucent), flexible rubber: 30 Shore A, 600% elongation

Where to use it

ASI lists sealing lead-wire entries, waterproofing electronics, circuit board protection, component mounting, electronic encapsulating and telecommunications work, including coaxial cable connectors. Typical bench jobs: sealing where a cable enters a housing, mounting a component to a board, covering a sensor or connection inside an outdoor enclosure. It bonds to glass, most metals, steel, vinyl, PVC, rubber and most painted surfaces.

How to use

1. Power down and disconnect the equipment before you start.
2. Clean and dry the surface. ASI recommends 100% isopropyl alcohol or acetone, depending on the substrate; do not use petroleum-based solvents.
3. Cut the nozzle, apply a bead or a small spot, and tool it within the 20-minute skin time.
4. Let it cure: about 24 hours for a 1/8″ bead. Thick or confined sections take longer, and cold or dry air slows the cure.
5. Allow 7 days for full strength before testing adhesion or loading the part.

Compatibility and cautions

ASI notes that 388 can discolor copper around the applied or confined area, so test it on exposed copper first. Adhesion to plastics varies (ASI lists “some plastics”); try a small bead and check it on day 7. While curing it releases methyl ethyl ketoxime (MEKO), and the SDS lists serious eye irritation, possible skin sensitization and suspected fertility effects. Wear gloves and eye protection, ventilate the area for 24 hours after application, and read the label and SDS on our technical documents page before use. ASI gives a 12-month shelf life when stored at 70°F and 50% RH.

Choosing between ASI 388, 502 and 509

For production work the same formula comes in an ASI 388 10.2 oz cartridge. For a general-purpose seal see ASI 502 clear 100% RTV silicone; for fish tanks, ASI 509 aquarium silicone sealant. Our guide to neutral-cure silicone for electronics explains the chemistry.