the first solder paste 30 melts down and the first electronic component 50 is adhered to the substrate 10 a heat treatment temperature during the reflow process should be higher than a melting temperature that is a soldering temperature of the first solder paste 30 and should be lower than a temperature that the first electronic component 50 can withstand accordingly an upper limit of the heat treatment temperature should be determined by considering temperature limits under which the first electronic component 50 has reliability referring to fig6 a second mask 22 and guides 60 are sequentially formed on the substrate 10 on which the first electronic component 50 is mounted the second mask 22 formed on the substrate 10 includes a second opening 14 through which the first electronic component 50 is exposed and a third opening 16 through which a region of the substrate 10 on which a second solder paste 32 of fig8 is to be applied is exposed the second mask 22 may be a thin metal layer like the first mask 20 the guide 60 formed on the second mask 22 barriers an introduction of the second solder paste into the first electronic component 50 the guide 60 is positioned on a portion of the second mask 22 which is between the first electronic component 50 and the region of the substrate 10 on which the second solder paste 32 is to be applied alternatively the guide 60 may be formed on a portion of the second mask 22 which is between the second opening 14 through which the first electronic component 50 is exposed and the third opening 16 through which the region of the substrate 10 on.