Effects of electroless copper plating on crystal continuity in via bottom

For advanced connecting reliability in micro-via holes, we have newly developed the electroless copper plating solution and investigated the features of the solution. With the conventional electroless copper plating solution containing nickel, when the thickness of electroless copper plating films is very small, the throwing power have dropped at the bottom corners of the micro-via holes; besides, the electrical resistance of the seed layers has increased at the same areas. With the developed solution without nickel but containing agents, it is possible to secure a low sheet resistance and high throwing power in micro- via holes; besides, high thermal resistance can be obtained after soldering because copper crystalline structure continues from the inner copper foil.