1. Field of the Invention
The present invention relates to a resin sealed-type semiconductor device, in which a semiconductor element and a lead for external connection are molded by a resin, and a method of manufacturing the same.
2. Description of the Related Art
With the advancement of an IC (integrated circuit) card and a memory card, it is requested that a semiconductor device which is incorporated into the card be thin and small. An example of the thin and small semiconductor device is a structure called CPS (chip size package) and the well-known example is described in Japanese Patent Application Laid-Open (JP-A) No. 9-17910. JP-A No. 9-17910 discloses a structure in which a lead frame is fixed to a semiconductor element, an electrode of the semiconductor element and the lead frame are connected electrically, a portion of the lead frame is sealed by a resin, and an outer terminal is provided on the surface of the lead frame which is not sealed by the resin.
However, the conventional resin sealed-type semiconductor device has following drawbacks.
When the pitch between the leads is narrow, the size of a solder bump which can be formed on the lead becomes small and the amount of solder is reduced. As a result, when the semiconductor device is disposed on a printed board and connected thereto, relaxation of stress by the solder is not sufficient and cracking may be formed on the solder bump which connects the printed board and the semiconductor device. In a case in which the solder bump is used in a severe temperature environment, the stress is directly and repeatedly applied to the solder bump due to the difference between the coefficient of thermal expansion of the portion sealed by the mold resin and the coefficient of thermal expansion of the printed board. The cracking is thereby generated due to the occurrence of brittle fracture on the solder bump.
Further, the solder bumps are formed in column of files on the plurality of leads and the distance between the solder bumps is short. As a result, if the pitch between the leads is narrow, the melted solder bumps contact at the time of mounting to the printed board or the like. Accordingly, a short circuit may occur between the adjacent leads.
Moreover, in a stage in which a product using the semiconductor device is manufactured, soldering is effected by heating the product in a reflow device at about 300.degree. C., and thereafter, when the product is cooled to an ordinary temperature, the stress is generated due to the difference between the coefficient of contraction of the sealed portion and the coefficient of contraction of the printed board. Consequently, cracking may be generated on the solder bump which has become especially fragile in the cooling process. It is difficult to find such cracking on the product during the inspection immediately after the product is manufactured, and the defective product may be shipped as a good item.