1. Field of the Invention
The present invention relates generally to an apparatus for stacking and soldering individual package devices for a three dimensional stack package device, and more particularly to such a stacking and soldering apparatus allowing automatic stacking and soldering by applying solder flux to metal portions of the individual package devices during the transfer of the package devices.
2. Description of the Related Arts
In present packaging technology, a three dimensional stacking of several integrated circuit devices has attracted attention in order to meet demands of high density and increased capacity. The three dimensional stack package device can be obtained by stacking non-packaged semiconductor bare chips or by stacking packaged individual devices. When the packaged devices are stacked, most of the existing assembly processes such as a die attachment, a wire bonding and a molding can be applied to the individual packages prior to stacking. However, specific additional processes are necessary in stacking the individual package devices.
In the package stacking technology, it is an important factor how to electrically interconnect the stacked devices. A soldering method is one of the widely used methods for the electrical interconnection.
FIG. 1A is a schematic diagram of a conventional soldering apparatus which is disclosed in U.S. Pat. No. 5,236,117, and FIG. 1B is a detailed view of FIG. 1A. Package devices 12 to be stacked are applied with a flux, and then fixed to the left end of an impact arm 10. When the metal part, e.g., outer leads of the package devices are heated to a predetermined temperature, the packages 12 are dipped into a molten solder fountain 8. The impact arm 10 is pivotally mounted on pivot assembly 6, which allows the left end of the impact arm holding the package device to move upward and downward. The impact arm 10a in an elevated position and the impact arm 10b in the lowered position are shown in FIG. 1A. When the impact arm 10 moves to its lower position, the outer leads of the package are dipped into the molten solder in the fountain 8. The height stopper 2 is to set the lowered position of the impact arm. Vibration means 4 is to vibrate the impact arm 10 in order to prevent solder voids or lack of solder tinning of closely spaced leads.
With this dipping technique, the solder application can be performed more efficiently. However, when the lead pitch gets finer as the package device requires more and more I/O pins, a solder bridge and therefore electrical shorting actions can occur. For solving these problems, impact weight 9 drops onto the top of the opposite end of the impact arm 10. Therefore, the package device and the impact arm are rapidly returned to the upper position, so that all of the excess molten solder is removed from the leads. The movement of the impact weight 9 is controlled by an air cylinder 7 which in turn may be controlled by a programmable controller.
In the conventional soldering apparatus explained above, loading process of the vertically stacked individual packages to the apparatus is performed manually. On the other hand, J-lead type individual packages such as SOJ (Small Outline J-bend), TSOJ (Thin SOJ) and PLCC (Plastic Leaded Chip Carrier) are suitably applied to the soldering for vertical interconnection of the three dimensional stack package device. Thus, if an automated stacking and soldering apparatus is provided for the exclusive use for the J-lead type packages, the mass production of the stack package device can be possible.