There is an established need for a water tight linear fixture in the CRS Electronics product line-up. This document evaluates the proposal for filling the standard product line with an encapsulant for the ultimate level of water protection. While using an encapsulant to fill the product has been demonstrated, there remain manufacturing time and complexity concerns with this approach. Several prototypes were created using several different manufacturing methods, with mixed results.
- IP 67: Total protection against dust ingress, protected against the effects of water immersion between 15cm and 1m depth.
- Minimal incremental cost over the product line.
- Minimal additional manufacturing time and complexity.
- For Class 1 Division 2
Full-fill of the cavity with an elastic encapsulant. To only provide sufficient depth to cover the electrical components would require approximately 50% less encapsulant than a full fill, but leaves an air gap for water and flammable vapour ingress into the remaining cavity. The additional encapsulant cost to fully fill the cavity and avoid these potential issues is judged to be worth it.
- Optically transparent (target >98% transparency across the visible spectrum at a 1cm depth)
- Elastic or compliant enough that differential thermal expansion/contraction during heating and cooling does not create enough internal stress to pop LEDs and electrical components off of the PCB
- Coefficient of thermal expansion should be similar enough to the MCPCB and casing that the lens is not substantially deformed or popped off during temperature cycling
- Non-yellowing with age
- UL 94 V0 Classification is desirable but may not be a hard requirement
- QSil 216: approx. $35.75/kg, elastic silicone, RT/heat cure, Tested w/ excellent initial results
- Shin-Etsu KE109A/B: $69.40/kg, elastic silicone, heat cure, Tested w/ good initial results (does not fully cure in centre of material – still gooey after approx. 1 hour around 100°C)
- Dow Corning Sylgard 184: $84.97/kg, elastic silicone, RT/heat cure, UL 94-V0 and Mil Spec
- GE Silicones RTV615: elastic silicone, optically clear
- Wacker Elastosil Solar 2202: soft silicone gel, “crystal clear”
- QSil 229LV: elastic silicone, heat cure, >98% transmittance
- Dow Corning PV-6010: “Silicone encapsulant that cures at low temperatures for solar applications” – NOT COMMERCIALLY AVAILABLE AS OF DEC 12 2012
- Dow Corning PV-6100: silicone gel, UL Pending, 99.5% transparent, heat cure (100°C) – NOT COMMERCIALLY AVAILABLE AS OF DEC 12 2012
Health and Safety
Most silicones are non-hazardous and no special handling precautions need to be carried out, other than use of gloves and glasses while working with liquid un-cured silicones. Both Shin-Etsu KE-109A and QSil 216 are considered non-hazardous. Health and safety concerns for other silicones will need to be assessed prior to use.
Prototypes and outcomes
1) Flat-filled 1-foot product – stock design except addition of elastomer gasket between end plates. This was an attempt to see if the fixtures could be filled in a horizontal layout, with the lens set into the un-cured silicone.
- Filled with Shin-Etsu KE109A/B through the top face with the lens removed. Lens installed while silicone is in an un-cured state.
- Leakage of silicone material at end plates due to gasket failure, and through screw-holes (w/ screws fully driven in). Created large bubbles under lens.
- Increased risk of silicone spillage and uneven depth due to un-leveled work surfaces and/or jostling during transport to the curing chamber.
- De-aeration of the silicone is particularly critical in this configuration as any air bubbles will be trapped directly beneath the lens.
- This orientation is not recommended for production.
2) Vertically-filled 1-foot product with edges and end-plate sealed with silicone. This was an attempt to see if fully assembled fixtures minus the end-plate could be easily filled in a vertical layout.
- To avoid silicone leakage, the lens and end plate were first sealed using standard clear GE Kitchen and Bath silicone.
- Filled with Shin-Etsu KE109A/B through the end-plate with the fixture in a vertical orientation.
- No leakage of silicone from lens or end plate seals.
- Minimal to no air bubbles affecting light output or directionality.
- Crude silicone sealing job on lens installation is clearly visible, otherwise no visual defects. With a more careful silicone job on the lens these visible defects can be avoided.
3) Sealing options for the lens and/or end plates:
- Manually silicone in end plate and lens prior to epoxy fill. Requires careful application of silicone, and at least 30 min to cure prior to encapsulant fill. Instant adhesive was also used with good sealing performance, but the chemistry of the instant adhesives will unacceptably haze the lens material.
- Manufacture improved gasket for sealing end plates and then seal lens in place with tape prior to encapsulant fill. The new gasket will need to seal the edges, cable through-hole, and screw holes. The hazardous location strain relief was found to leak at threaded joint in one instance (De-Ox was applied to threads prior to assembly) and in several instances silicone was seen to leak out through the end-plate mounting holes with screws installed.
- Several types of tape were tested, with Duct Tape providing an adequate seal between the lens and the body. The end plate geometry with cable input is too complicated for tape to provide an adequate seal.
- Mixing bucket w/ lid: approx. $5 per batch
- Epoxy cost: