Printed circuit board having permanent solder mask

A printed circuit board having a permanent solder mask comprising:

• a substrate made of a material including a first resin, said substrate having top and bottom surfaces, a first conductive pattern disposed on said top surface and having an unsheltered portion and a sheltered portion, said unsheltered portion having a base and a tip;
• and
• a first solder mask made of a second resin having a thermal expansion coefficient substantially identical to that of said first resin of said substrate, said first solder mask coated on said top surface in such a way that a layer having a first area and a second area is formed thereon, said first area having a first thickness, a smooth outer surface, and covering said sheltered portion, said second area having a second thickness less than that of said first area and surrounding said base of said unsheltered portion such that said tip of said unsheltered portion is exposed outside.