Circuit board for ink jet head, method of manufacturing the same, and ink jet head using the same

An ink jet head circuit board comprising:

• a board;
• a resistor layer formed on the board;
• a pair of first electrode layers disposed on the resistor layer with a gap so as to be opposed to each other, the resistor layer forming a heater at a portion corresponding to the gap so as not to be covered with the first electrode layers;
• a first protective layer entirely covering the portion of the resistor layer corresponding to the gap and covering the pair of the first electrode layers;
• a second electrode layer formed on the first protective layer except at least over the gap and electrically connected to at least one of the pair of first electrode layers, the second electrode layer being greater in thickness than an edge of the first electrode layers facing the gap;
• a second protective layer formed on the second electrode layer to cover the first protective layer except at least a portion of the first protective layer corresponding to the gap, the second protective layer being greater in thickness than the first protective layer,
• wherein the first protective layer is formed as a single continuous layer.