Liquid ejection unit and method for manufacturing liquid ejection unit

A method for manufacturing a liquid ejection unit comprising a liquid ejection chip and a wiring substrate connected to the liquid ejection chip, wherein

• the liquid ejection chip comprises:
• an ejection element that generates energy for ejecting liquid;
• a liquid ejection substrate on which the ejection element is provided;
• and
• an electrode part provided on the liquid ejection substrate for driving the ejection element;
• and
• the wiring substrate has electrode parts that can be electrically connected to the electrode parts of the liquid ejection chip;
• the manufacturing method comprising:
• a step of preparing the liquid ejection chip and the wiring substrate;
• a step of hydrophilizing the electrode part at the liquid ejection chip;
• and
• a step of bringing the hydrophilized electrode part at the liquid ejection chip into contact with the electrode part at the wiring substrate to enable electrical connection, and bonding the parts with a non-conductive adhesive to obtain the liquid ejection unit, wherein
• the hydrophilizing step is a step of treating so that a surface free energy of the electrode part at the liquid ejection chip is 65 to 150 dyne/cm,
• the non-conductive adhesive contains a filler, and
• a surface free energy of the filler is 55 dyne/cm or less.