Silicone potting compound

Pick silicone potting (TIG680 / TIS680) when the pour must survive thermal cycling, vibration, or wide-temperature service (−50 to +200 °C). Cured silicone is soft and elastic, so CTE mismatch with copper or aluminum doesn't crack the pour. Pick epoxy potting (TIE280-AB) when you need rigid mechanical reinforcement, top-class moisture barrier, or chemical resistance to fuels and solvents. Silicone is also reworkable — cured silicone can be cut and re-poured; cured epoxy cannot.

TIG680 is a lightly-filled silicone with simpler mix and slightly lower density; the family ladder is 15/20/28/30/40 corresponding to 1.5 / 2.0 / 2.8 / 3.0 / 4.0 W/m·K and a soft Shore A 25 – 45 post-cure. TIS680 is heavily-filled with higher ceramic loading; it covers 1.0 – 3.5 W/m·K with varied hardness (Shore A 65 / Shore D 85 / Shore 00 soft-gel options) tuned to whether the pour is acting as structural reinforcement or stress-relief gel.

Open Part A and Part B, weigh out 1:1 (1:1 by volume in most TIG680 grades, 1:1 by weight in TIS680 grades — confirm per datasheet), mix under low shear for 3 – 5 minutes, degas under vacuum if the application is dielectric-critical or high-voltage, and pour into the cavity. Pot life is typically 30 – 60 minutes at 25 °C; full cure 24 hours at room temp or accelerated 80 °C / 30 min. For high-volume production, a meter-mix-dispense (MMD) machine with static mixing tip handles A/B ratio control automatically.

Cured silicone has a low Young's modulus (typical 1 – 10 MPa) compared to cured epoxy (1 – 5 GPa — three orders of magnitude stiffer). When the encapsulated assembly cycles between −40 and +130 °C, copper expands more than the silicone — the soft silicone simply stretches around the components without cracking. A rigid epoxy will eventually fatigue-crack at the silicone-copper interface or fracture deep pours over large copper planes. For applications with > 50 K thermal swing or high cycle count, silicone is almost always the right call.

Yes — cured silicone can be cut with a sharp blade, the failed component replaced, and a fresh pour poured into the void to re-encapsulate. The new silicone bonds to the cured layer if the surface is clean. This is a unique advantage over epoxy potting, where rework usually means scrapping the assembly. Mark the access location at design time so the technician knows where to cut.

Two-component addition-cure silicones (most TIG680 and TIS680 grades) outgas significantly less than one-part RTV silicones — there's no acetic acid release because the cure is by platinum-catalysed hydrosilylation. For ultra-clean applications (CCD packaging, hermetic relays, MEMS) confirm the per-grade outgassing data sheet (TML / CVCM values per ASTM E595). Heat-cured grades typically out-perform RT-cured grades on outgassing because residual volatiles are driven off during the bake.