Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device comprising a circuit board having a number of electrode portions on a front side and an underside, an electronic circuit element bonded to the electrode portions on the front side of the circuit board and composing an electronic circuit, and a plurality of ball electrodes for external connection, the ball electrodes being formed on the electrode portions on the underside of the circuit board, the method comprising the steps of:

• forming the (plurality of) electrode portions on the underside of the circuit board such that the electrode portion on an outer periphery is larger than the electrode portion on an inner periphery;
• and forming the plurality of ball electrodes by mounting solder balls containing tin and silver but not containing lead on the electrode portions on the underside of the board, and heating and melting the solder balls to form an alloy on surfaces of the electrode portions, and meanwhile cooling, from the electrode portions, the solder balls having been melted on the electrode portions on the outer periphery.