Liquid ejection head and production method for producing same

A method for producing a liquid ejection head, the method comprising the steps of:

• preparing an element substrate in which a liquid ejection port is formed, the element substrate having an energy generating element that generates energy for ejecting the liquid from the liquid ejection port, and a plurality of wiring pads aligned in a predetermined direction;
• preparing a flexible wiring substrate having a plurality of leads aligned in the predetermined direction and overlaid on and connected to, respectively, the plurality of wiring pads, and a base film overlaid on the plurality of leads at a side opposite to that of the plurality of wiring pads;
• respectively connecting the plurality of leads to the plurality of wiring pads;
• and
• sealing, by a sealant, a plurality of connection portions of the plurality of wiring pads and the plurality of leads,
• wherein the base film has:
• a plurality of covering portions that respectively cover the plurality of leads at a side opposite to that of the plurality of connection portions;
• and
• an opening or slit formed between the plurality of covering portions.