Rogers' laminates are supplied as a fully cured thermoset or thermoplastic product, so the dielectric materials making up the laminates are stable given reasonable storage environments. Copper oxidation can occur under humidity and temperature and, if excessive will oxidize to a point that normal processing conditions will not remove the oxidation for use in imaging at the board shop. In most cases, a light level of oxidation can be removed by a micro-etch and/or pumice scrubbing. There is no defined shelf life for Rogers laminate material as long as the copper surface is not severely oxidized and reasonable storage environments are maintained. The best practice is to store the material in its original packaging.
Bond-ply or Prepreg is a different product, by definition a partially cured dielectric containing polymers and other additives. IPC requires the following:
Bonding Layer Shelf Life
Unless otherwise specified, bonding layers supplied shall be capable and certified to meet all the requirements specified when stored either as per Condition 1 for not less that 180 days after receipt of shipment by the user, per Condition 2 for not less than 90 days after receipt of the shipment by the user, or as agreed upon between the user and supplier.
Condition 1: <4.5°C (<40.1°F)
Condition 2: 21°C ± -2°C (69.8°F ± -3.64F), Relative humidity: 30% to 50%
Rogers RO4450 prepregs should be stored between 50°F and 85°F in low humidity and are valid for one year from the date of manufacture. The bonding layer should be stored in the absence of a non-catalytic environment such as UV light or excessive radiation.