Thermal Grease Bleeding after Opening? Re‑Inspection and Material Selection for SIGR 2235

If thermal grease shows obvious free oil, paste separation or local agglomeration once opened, it is not recommended for direct use in electronic power modules without re‑qualification. It shall first be determined whether the change represents an acceptable storage drift or abnormal loss of material homogeneity. ELAPLUS SIGR 2235 thermal grease may be evaluated for thermal interfaces of IGBTs, DC/DC converters and other power devices; nevertheless, release criteria must be established with reference to material condition, application process and actual thermal performance. Thermal grease generally consists of base oil and thermally conductive fillers. It is a non‑crosslinking paste and relies on no curing reaction to form a thermal interface. Its storage condition can be affected by temperature cycling, shelf time, transit vibration and the inherent formulation. Surface gloss, local liquid exudation or uneven colour after opening do not automatically render the material invalid, nor can it be simply stirred and fed directly into mass production. The correct workflow is to confirm usability by visual inspection, homogeneity check, application performance and functional testing. 1. Why Does Thermal Grease Bleed or Separate? Conductive fillers and base oil serve distinct roles inside thermal grease: fillers build the primary thermal conduction network, while base oil facilitates filler wetting and enables the paste to spread and fill micro‑irregularities on mating surfaces. Prolonged storage or temperature fluctuation may trigger redistribution of the liquid phase, filler sedimentation or local viscosity variation. Formulations differ in sensitivity to these factors, so the state of one grease grade cannot be adopted as the acceptance standard for all products. A faint oily sheen on top of the container with homogeneous bulk paste does not necessarily indicate failure. Visible free liquid layer, hardened sediment at the bottom or irreversible particle agglomeration, by contrast, call for close scrutiny. Additional checks shall cover package…