1. Technical Field
The present disclosure relates to an apparatus and method of mounting one conductive ball on each of a plurality of connection pads on a substrate.
2. Related Art
Upon forming the solder bumps on the connection pads for flip-chip bonding formed on a substrate such as a wafer or a circuit substrate, in the related art, a solder paste is coated by the screen printing and then fused by reflow soldering. In this case, with higher packaging density of a semiconductor device, a fine pitch such as 200 μm or strictly 150 μm is demanded as a bump pitch. When the solder paste is coated by the screen printing at such a fine pitch, a bridge between the bumps or adhesion of the solder paste to a printing mask occurs. Therefore, it is difficult to form the solder bumps at a fine pitch by the screen printing.
For this reason, as a method of forming the bumps at a fine pitch, it is considered that the solder balls are arranged on the connection pads.
As one method, there has been known a method of chucking solder balls with a chucking jig to carry the solder balls and then mounting the solder balls on connection pads. The method is applied to board mounting connection pads on an external connection terminal side of Ball Grid Array (BGA). The adhesive soldering flux is coated on the connection pads in advance, and then the solder balls are adhered/secured onto the connection pads respectively. Then, the bumps are formed by reflowing the solder balls. In this case, a diameter of the solder ball is as large as about 0.3 to 0.7 mm. In contrast a diameter of the solder ball used at a fine pitch must be reduced to 100 μm or less. When a size of the solder ball becomes smaller in this manner, such a problem is caused that the solder balls are clumped by an action of the static charges or the solder ball cannot be chucked exactly into a chucking port of the chucking jig due to the influence of an airflow. Also, the chucking port of the chucking jig needs to be miniaturized in size and also a manufacturing cost is increased. As a result, this method is not practical in use.
Therefore, as another method, there has been known a method of feeding solder balls into each opening of a mask placed on a substrate (so-called a “feeding method” hereinafter). That is, the flux is coated on the connection pads of the substrate, then the metal mask is aligned with the pads and then is overlapped thereon. The solder balls are fed from the upper side of the metal mask, and then the solder ball is dropped into openings of the metal mask respectively. The solder balls are dropped down from a container having an opening such as a slit on a bottom surface thereof. The opening is designed such that the solder balls are dropped onto the mask with a proper amount. One solder ball is fed into each opening of the mask and is mounted on the connection pad that is aligned with the opening, and then is adhered/secured to the connection pad by the adhesive flux coated on the connection pads. The solder balls remaining on the mask are recovered by the recovering mechanism.
According to this method, the mask is not brought into contact with the ball feeding head (container), and an air gap is formed to be the ball diameter or less. For example, JP-A-2002-151539 discloses that balls are not overlapped with each other and are aligned on one layer by controlling an air gap. Also, JP-A-2006-318994 discloses that the gap is controlled to be smaller than the ball diameter such that the balls are not left on the mask.
However, in the method of maintaining the gap between the mask and the head, the balls might be pinched between the mask and the head, and then be deformed. In particular, in the case of the circuit substrate (resin substrate), warpage becomes large and also an unevenness in thickness of the substrate becomes large. As a result, when a size of the substrate is large, it is very difficult to uniformly maintain the gap between the mask and the head over the whole substrate, and thus it is impossible to avoid such an event that the balls are pinched between the mask and head.