Method for manufacturing a printed circuit board for electronic devices and an electronic device using the same

A method for manufacturing a lead-free printed circuit board for electronic devices comprising:

• applying a first solder paste having a Sn—Bi solder component without Ag onto a first plurality of electrodes formed on a printed circuit;
• applying a second solder paste having a Sn—Bi—Ag solder component onto a second plurality of electrodes formed on the printed circuit;
• applying a first group of electronic parts having a first group of connection terminals with a metal composition comprising Sn, Ag and Cu onto said first solder paste;
• placing a second group of electronic parts having a second group of connection terminals with a metal composition comprising Sn and Bi and without Ag onto said second solder paste;
• and
• heating said first solder paste, second solder paste, first group of connection terminals, and second group of connection terminals.

A method for manufacturing a lead-free printed circuit board for electronic devices with a substrate to which a plurality of electronic parts having connection terminals with different metal compositions are connected by soldering, wherein:

• a plurality of solder pastes comprising solder components with different compositions are used;
• said plurality of solder pastes comprising solder components with different compositions comprise a solder paste having a Sn—Bi solder component without Ag, and a solder paste having a Sn—Bi—Ag solder component;
• when said electronic parts are connected by soldering to said substrate, a solder paste having a solder component with a different composition is used for each of the metal compositions for the connection terminals of electronic parts;
• when Ag is present at connection terminals of an electronic part to be connected by soldering, said solder paste having a Sn—Bi solder component without Ag is applied only to the substrate electrodes corresponding to the connection terminals with Ag thereat, and when Ag is absent at connection terminals of an electronic part to be connected by soldering, said solder paste having a Sn—Bi—Ag solder component is applied only to the substrate electrodes corresponding to the connection terminals without Ag thereat;
• and
• wherein, in said case in which Ag is present at connection terminals of an electronic part to be connected by soldering, said connection terminals with Ag thereat have a metal composition of Sn-3Ag-0.5Cu, and in said case in which Ag is absent at connection terminals of an electronic part to be connected by soldering, said connection terminals without Ag thereat have a metal composition of Sn-3Bi.