Electronic device having a plurality of metallic balls for transmitting signals between two circuit boards

A method of connecting a primary circuit board with a secondary circuit board, at least an electronic component being set on the primary circuit board, the secondary circuit board comprising a first side and a second side, and a plurality of electronic components being set on the first side of the secondary circuit board, the method comprising:

• adhering a plurality of metallic balls to the second side of the secondary circuit board;
• heating and melting the plurality of metallic balls in accordance with a particular relationship between temperature and time, to make the plurality of metallic balls connect with the secondary circuit board;
• bonding the plurality of metallic balls connected with the second side of the secondary circuit board to the primary circuit board;
• and
• heating and melting the plurality of metallic balls bonded to the primary circuit board in accordance with the particular relationship between temperature and time, to make the primary circuit board connect with the secondary circuit board by means of the plurality of metallic balls;
• wherein the plurality of metallic balls is used for signal transmission between the plurality of electronic components on the first side of the secondary circuit board and the electronic component on the primary circuit board.