Connection method, connection structure, and electronic device

A connection method comprising:

• a step (a2) of preparing a base material including an electrode for connection using an adhesive and an electrode for connection using solder;
• a step (b2) of covering only the electrode for connection using solder with an organic film formed by OSP treatment or a noble metal plating film, the electrode for connection using solder being arranged on the base material;
• a step (c2) of joining the electrode for connection using solder to a connection conductor using solder by solder reflow treatment in a non-oxidizing atmosphere;
• and
• after the step (c2), a step (d2) of bonding the electrode for connection using an adhesive to a connection conductor with an adhesive mainly containing a thermosetting resin to establish electrical connection.

A connection method comprising:

• a step (a3) of preparing a base material including an electrode for connection using an adhesive and an electrode for connection using solder;
• a step (b3) of covering the electrode for connection using an adhesive and the electrode for connection using solder with oxidation preventing films, the electrode for connection using an adhesive and the electrode for connection using solder being arranged on the base material;
• after the step (b3), a step (c3) of bonding the electrode for connection using an adhesive to a connection conductor with an adhesive mainly containing a thermosetting resin to establish electrical connection;
• and
• after the step (c3), a step (d3) of joining the electrode for connection using solder to a connection conductor using solder by solder reflow treatment in a non-oxidizing atmosphere,
• wherein an increase in connection resistance between the electrode for connection using an adhesive and the connection conductor before and after the step (d3) is within a predetermined range.