Electroplating processor with thin membrane support

An electroplating processor includes a thin lower membrane support for supporting a membrane. The lower membrane support may be provided as a flexible plastic sheet having a pattern of through-openings. The through-openings may be aligned with openings in a rigid upper membrane support. The perimeter of the lower membrane may be clamped in the same perimeter seal as used to clamp and seal the perimeter of the membrane. The lower membrane support supports the membrane without adding significantly to the overall height of the processor. The processor can be stacked in a two level processing system without requiring additional clean room space.