In photovoltaic junction boxes and module-level power electronics, addition-cure silicone potting compounds supplied by Runhe Materials (Zhuhai) Co., Ltd. are dispensed through positive-displacement meter-mix equipment with static mixers of 10 mm to 16 mm internal diameter at a volumetric ratio of 1:1 and mixed viscosity between 1200 mPa·s and 4000 mPa·s at 25 °C. The compound is vacuum-degassed at −0.09 MPa for 120 s before dispensing to reduce void formation at the PPO or PA66 junction box wall interface; this step is critical because entrapped air lowers partial discharge inception voltage and creates hot spots during IEC 61215:2021 MQT 11 thermal cycling between −40 °C and 85 °C. After heat acceleration at 80 °C for 30 min or 7 days at 23 °C, the cured elastomer exhibits volume resistivity above 1×1015 Ω·cm per ASTM D257 and dielectric strength not less than 18 kV/mm for a 2 mm specimen per ASTM D149; these values support 1500 V system voltage insulation coordination under IEC 60664-1 pollution degree 3 conditions. Adhesion to aluminum and glass-filled PPO, measured as lap shear per ASTM D1002, is maintained in the range 1.0 MPa to 2.5 MPa after 1000 h damp heat at 85 °C and 85 % RH per IEC 61215:2021 MQT 13; total chloride and sodium ion content is controlled below 5 ppm each to reduce electrochemical migration leakage current. Processing boundary: substrates must be free of tin-catalyzed condensation residues and sulfur-containing rubber gaskets, because these species inhibit platinum cure and produce a tacky surface; published data for this specific configuration is limited where continuous immersion in acidic solutions is required.
How Does Low Cyclic Siloxane Outgassing Prevent PID and Contact Degradation?
The dominant chemical pathway for potential-induced degradation in glass-glass module architectures involves migration of sodium ions from cover glass through the cell stack; non-conductive siloxane films can further disrupt surface conductivity balance when cyclic dimethylsiloxane oligomers in the D4 to D10 range evaporate from the encapsulant and deposit on cell busbars. Addition-cure silicone materials from Runhe Materials (Zhuhai) Co., Ltd. are therefore manufactured with reduced volatile condensable material, showing total mass loss of ≤0.05 % and collected volatile condensable material of ≤0.01 % when tested according to ASTM E595 after 24 h at 125 °C under 10−3 Pa vacuum. Residual D4 to D10 cyclic siloxane concentration in the cured network is limited to ≤150 ppm by headspace gas chromatography–mass spectrometry at 200 °C; this minimizes siloxane deposition on silver-plated copper junction box contacts and keeps contact temperature rise below 50 K during IEC 62790 diode current tests. Platinum cure can be inhibited by amine-based additives, tin soaps, and sulfur-containing elastomers; pre-production compatibility testing per ASTM D4285 is required when wire insulation or conformal coating exists adjacent to uncured silicone. Post-cure at 150 °C for 2 h further reduces volatile siloxane concentration and stabilizes adhesion to busbar passivation layers.
For conformal coating of onboard charger, DC-DC converter, and battery management system printed circuit assemblies, a solventless silicone conformal coating is applied by selective robotic spray at dry film thickness of 50 µm to 150 µm using needle diameters of 0.2 mm to 0.8 mm and atomization air pressure of 0.2 MPa to 0.5 MPa; the coating is tack-free within 15 min at 23 °C and full cure after 72 h at 23 °C or 20 min at 80 °C. Under IPC-CC-830B qualification, the coated assembly passes surface insulation resistance testing per IPC-TM-650 2.6.3.3 with minimum 1×109 Ω after 168 h at 85 °C and 85 % RH with 50 V DC bias; dielectric withstand per IPC-TM-650 2.5.6.1 remains above 1000 V AC for 60 s at 60 Hz. The coating reduces electrochemical migration on fine-pitch conductors under 0.5 mm spacing because the silicone has high hydrophobicity with contact angle of water droplet 98° to 105° measured per ASTM D7490; condensation droplets do not form continuous films. Because the coating is solventless and platinum-catalyzed, mixed material pot life is limited to 4 h to 8 h at 25 °C; process equipment must use chilled static mixers below 15 °C for long production runs. Published data for this specific configuration is limited when sprayed over acrylic-based conformal coatings, and adhesion must be verified by cross-hatch per ASTM D3359.
Thermal Interface Gap Filling for Cylindrical Cell-to-Pack Modules
Cylindrical lithium-ion cells assembled into cell-to-pack structures create localized heat flux densities above 10 kW/m² at cell shoulders during 2C discharge, requiring a thermally conductive silicone gap filler that can accommodate cell insertion tolerance while maintaining interface pressure below 50 kPa to avoid can deformation. Two-part addition-cure gap fillers from Runhe Materials (Zhuhai) Co., Ltd. are formulated with aluminum oxide and zinc oxide fillers to give thermal conductivity of 2.5 W/m·K to 4.0 W/m·K measured per ASTM D5470 at 10 % compression and 80 °C hot-plate temperature; density is 2.6 g/cm³ to 3.2 g/cm³ per ASTM D792, and Shore OO hardness is 35 to 60 per ASTM D2240 after 24 h at 23 °C. The material is dispensed through follower-plate pumping systems with 25:1 ratio rams and progressive cavity pumps at volumetric flow rates of 10 mL/min to 60 mL/min; static mixing elements of 18 to 24 stages are required to eliminate filler striation. Mixed viscosity at 10 s⁻¹ and 25 °C is 80 Pa·s to 250 Pa·s, with thixotropic index of 2.5 to 4.0 between 1 s⁻¹ and 10 s⁻¹, so the bead retains its position after dispensing but flows under cell insertion force. Under ISO 16750-3 random vibration at 27.8 m/s² RMS for 8 h per axis and thermal shock from −40 °C to 85 °C for 100 cycles, the cured gap filler shows no interfacial delamination exceeding 5 % of bond area when measured by scanning acoustic microscopy; thermal resistance after vibration increases by less than 10 %. Filler sedimentation during storage requires re-homogenization by slow planetary mixing at 20 rpm for 30 min if containers remain static for more than 6 months; cure inhibition occurs in contact with sulfur-containing rubber cell holders and amine-cured epoxies, so compatibility testing per ASTM D4285 is required.
Table 1. Comparative cured properties of Runhe silicone classes used in new energy and PV assembly.
| Property | Test method | Addition-cure encapsulant | Thermal gap filler | Condensation-cure sealant |
|---|---|---|---|---|
| Hardness | ASTM D2240 | Shore A 45–65 | Shore OO 35–60 | Shore A 25–45 |
| Tensile strength | ISO 37 | 1.5–3.5 MPa | 0.5–1.5 MPa | 1.0–2.5 MPa |
| Elongation at break | ISO 37 | 80–200 % | 50–100 % | 200–500 % |
| Volume resistivity | ASTM D257 | 1×1015 Ω·cm | 1×1013 Ω·cm | 1×1014 Ω·cm |
| Dielectric strength | ASTM D149 | 18–22 kV/mm | 8–12 kV/mm | 14–18 kV/mm |
| Thermal conductivity | ASTM D5470 | 0.2 W/m·K | 2.5–4.0 W/m·K | 0.25 W/m·K |
| Compression set | ASTM D395 B | 10–30 % | 5–15 % | 10–25 % |
| Flame rating | UL 94 | V-0 at 3 mm | V-0 at 2 mm | HB at 3 mm |
Where high-voltage battery pack enclosure gaskets require continuous clamping force under thermal cycling, condensation-cure alkoxy silicone sealants supplied by Runhe Materials (Zhuhai) Co., Ltd. are deposited as formed-in-place gaskets by six-axis robots using 2.5 mm stainless-steel nozzles at extrusion pressure 0.4 MPa to 0.8 MPa and bead width 4 mm to 8 mm. The cured sealant reaches tack-free condition within 20 min and achieves gross cure at 3 mm thickness after 24 h at 23 °C and 50 % RH; full adhesion to aluminum and galvanized steel flanges is obtained after 7 days. Compression set after 22 h at 100 °C per ASTM D395 Method B is below 15 %, allowing flange clamping force retention above 80 % after 1000 h at 85 °C. Tensile strength is 2.0 MPa to 3.0 MPa and elongation at break is 300 % to 500 % per ISO 37; tear strength exceeds 5 kN/m per ASTM D624, preventing gasket extrusion through 0.5 mm flange gaps. The sealant resists engine coolant, transmission fluid, and 5 wt% salt mist per ASTM B117 for 500 h with no loss of adhesion; volume resistivity after damp heat is 1×1014 Ω·cm per ASTM D257. Not recommended for continuous immersion in dielectric coolant fluids without published long-term compatibility data; use addition-cure fluorosilicone if sustained contact with aggressive esters or ketones is specified.
When Potting of Power Optimizers and Microinverters Demands Flame-Retardant and Thermal-Shock Resistance
Power optimizers mounted under PV modules operate at internal temperatures that can exceed 90 °C during peak irradiance; the silicone potting compound must therefore combine UL 94 V-0 flammability at 3 mm thickness with a comparative tracking index of ≥600 V per IEC 60112 to protect against surface carbonization under polluted surface conditions. Runhe Materials addition-cure flame-retardant silicone is formulated with alumina trihydrate and melamine polyphosphate fillers, yielding halogen-free combustion gas with pH >4.3 and conductivity <10 µS/cm per IEC 60754-2, and limiting smoke density to DS max <200 per ISO 5659-2 at 25 kW/m². The potting layer is subjected to IEC 60068-2-14 thermal shock from −40 °C to 105 °C for 200 cycles with 15 min dwell; crack-initiating stress at sharp corners is controlled by maintaining cured hardness below Shore A 55 and elongation above 100 % per ISO 37. The compound cures at 65 °C for 60 min in multi-cavity molds with no solvent evolution; post-cure at 120 °C for 2 h stabilizes filler-matrix adhesion and reduces post-cure hardness drift to ≤3 Shore A points. Dielectric breakdown remains ≥14 kV/mm per ASTM D149 after thermal shock; volume resistivity is 1×1014 Ω·cm per ASTM D257 at 500 V DC after 85 °C/85 % RH for 1000 h. Formulations containing melamine polyphosphate may display viscosity increase after 3 months storage at 35 °C; drum rotation and temperature-controlled storage below 25 °C are required. Platinum catalyst inhibition from tin-catalyzed component leads or sulfur-containing cable jackets must be excluded by batch-level cure testing before potting.
Table 2. Qualification matrix for silicone materials in PV and new energy power electronics.
| Requirement | Standard / Test method | Acceptance criterion |
|---|---|---|
| Outdoor UV stability | ASTM G154 Cycle 1, 2000 h | Shore A change ≤ 5 points |
| Damp heat insulation | IEC 61215:2021 MQT 13 | Volume resistivity ≥ 1×1014 Ω·cm |
| Flammability | UL 94 | V-0 at 3 mm |
| Tracking index | IEC 60112 | ≥600 V |
| Outgassing | ASTM E595 | TML ≤ 0.05 %; CVCM ≤ 0.01 % |
| Thermal conductivity | ASTM D5470 | 2.5–4.0 W/m·K for gap filler |
| Dielectric strength | ASTM D149 | ≥ 18 kV/mm for encapsulant, 2 mm |
| Compression set | ASTM D395 B | <15 % after 22 h at 100 °C |
| Salt spray | ASTM B117 | 500–1000 h no adhesion loss |
| Thermal shock | IEC 60068-2-14 | 200 cycles −40 °C ↔ 105 °C, no cracking |
During qualification of building-integrated photovoltaic and floating solar arrays using IEC 61730-2 and ASTM G154 cycle 1 UV exposure at 0.89 W/m²·nm at 340 nm for 2000 h, silicone edge sealants supplied by Runhe Materials (Zhuhai) Co., Ltd. demonstrate Shore A hardness change of ≤5 points and elongation retention above 90 % relative to unexposed controls per ISO 37. The sealant's water vapor transmission rate is 20 g/m²·day to 40 g/m²·day for a 2 mm cured sheet per ASTM E96 Procedure B, which is intentionally higher than polyisobutylene edge tape but permits moisture egress after latent moisture ingress while maintaining adhesion to glass and backsheet under wind-load flexure. Floating PV installations additionally require resistance to 5 wt% sodium chloride fog per ASTM B117 for 1000 h; the sealant retains ≥85 % initial lap shear on glass and aluminum after exposure. The low modulus of 0.5 MPa to 1.0 MPa at 100 % elongation minimizes stress on thin-film solar cells during thermal expansion mismatch. For continuous immersion in brackish water or exposure to organic solvents used for panel cleaning, published data for this specific configuration is limited; a field splice test or ASTM C794 adhesion-in-peel after immersion is required before specifying this material.
