The present invention relates to a semiconductor device and particularly, a structure of a plastic ball grid array package (referred to as P-BGA hereinafter). 
The structure of a common P-BGA is explained referring to the relevant drawings. 
FIG.  11 is a cross-sectional view of the P-BGA and FIG.  12 is an enlarged view showing the region A of FIG.  11. 
Shown are an organic substrate 1, a copper foil wiring pattern 2, a semiconductor chip 4, bonding wires 5, a sealing resin 7, a resist 8, a grounding layer 9, and solder paste balls 12. 
For production of the P-BGA structure, general steps are (1) coating the organic substrate 1, made of e.g. bismaleic triazine resin and equipped with the copper foil wiring pattern 2 having a thickness of 10 to 40 micrometers, with the resist 8 for protecting most regions of the wiring pattern 2 where no bonding wires are connected, placing the semiconductor chip 4 by a conductive paste on the substrate 1, (2) connecting electrodes of the semiconductor chip 4 by the bonding wires 5 to the wiring pattern 2 on the organic substrate 1, (3) sealing with the sealing resin 7 one side of the substrate 1 where the semiconductor chip 4 is mounted, and (4) applying a grid form of balls 12 on the other side of the substrate 1. 
The conventional P-BGA however allows the resist 8, which contains a silicon component unfavorable for adhesiveness to the sealing resin 7, to cover most regions of the organic substrate 1 to be sealed with the sealing resin 7.  The sealing resin 7 of a particular type may cause the resist 8 to release its silicon component as triggered by a thermal history in the sealing or reflow process during the mounting to a mother board, and subsequently detach at its interface from the sealing resin 7, thus reducing the resistance to moisture.