A female structure embedding a first metal pillar and a male structure embedding a second metal pillar. The female structure and the male structure can be locked in with each other, the embedded first metal pillar electrically coupled to the second metal pillar through a metal block. The metal block is electrically coupled to a bottom surface of the first metal pillar, and the metal block wraps peripheral surface of a top end of the second metal pillar. A first embodiment shows the metal block is formed by electroless deposition after matching the female structure to the male structure. A second embodiment shows the metal block is a solder joint.