A solder pad structure with a high bondability to a solder ball is provided. The present invention provides a larger contact area with the solder ball so as to increase the bondability according to the principle that the bondability is positive proportional with the contact area therebetween. The solder pad structure includes a circuit board having a solder pad opening defined by a solder resist layer surrounding a circuit layer. The circuit layer within the solder pad opening is defined as a solder pad. In such a way, after filling the solder ball into the solder pad opening, besides walls of the solder pad opening, there is an extra contact area provided by a geometric shape of the solder pad for further improving the bondability of the solder pad and the solder ball.