Process inner-layers through develop, etch, and strip using standard industry practices. Use brown oxide on inner layers. Adjust dwell time in the oxide bath to ensure uniform coating. Bake inner layers in a rack for 60 minutes at 107°C - 121°C (225°F - 250°F) immediately prior to lay-up. Store prepreg at 60-70°F at or below 30% RH. Vacuum desiccate the prepreg for 8 - 12 hours prior to lamination.

Lamination Cycle:

1. Pre-vacuum for 30 - 45 minutes
2. Control the heat rise to 4.5°C - 6.5°C (8°F - 12°F) per minute between 100°C and150°C (210°F and 300°F). Vacuum lamination is preferred. Start point vacuum lamination pressures are shown in the table below.
3. Set cure temperature at 213˚C (415˚F). Start cure time when product temperature > 210˚ C (410˚F)
4. Cure time at temperature = 90 minutes
   NOTE: For sequential lamination use 60 minutes for the first lamination and 90 minutes for the final.

• Drill at 350 SFM. Undercut bits are recommended for vias 0.0 18” (0.45mm) and smaller
• De-smear using alkaline permanganate or plasma with settings appropriate for polyimide; plasma is preferred for positive etchback
• Conventional plating processes are compatible with 35N
• Standard profiling parameters may be used; chip breaker style router bits are not recommended
• Bake for 1 - 2 hours at 250°F (121°C) prior to solder to reflow of HASL