Package structure for a semiconductor device

A package structure for a semiconductor device comprises a substrate having a main surface and a back surface, a semiconductor chip formed on the main surface of the substrate, a package covering the semiconductor chip, radiation protrude electrodes and connection protrude electrodes. The radiation protrude electrodes are formed on the back surface of the substrate in a chip area where said semiconductor chip is located. Each of the radiation protrude electrodes are formed with a first pitch so that the radiation protrude electrodes make one body joining layer when the package structure is subjected to a heat treatment. The connection protrude electrodes are formed on the back surface of the substrate in a peripheral area of the chip area. Each of the connection protrude electrodes formed with a second pitch which is larger than the first pitch so that the connection protrude electrodes stay individual when the package structure is subjected to a heat treatment.

BACKGROUND OF THE INVENTION

The present invention relates to a package structure for a semiconductor device, and more particularly, it relates to a package structure having radiation solder bumps and connection solder bumps on a back surface of the package structure.

A conventional semiconductor device includes a package for covering a semiconductor chip, a substrate having a main surface on which the semiconductor chip is formed and radiation solder bumps and connection solder bumps formed on the back surface of the substrate.

The radiation solder bumps are formed in the center area of the back surface of the substrate. The connection solder bumps are formed in the peripheral area which surrounds the center area of the substrate. The connection solder bumps are electrically connected to electrodes of the semiconductor chip through conductive lines formed in the substrate. Therefore, the connection solder bumps have a function as terminals for connecting the semiconductor device to an outside circuit.

When the semiconductor device is mounted on a circuit board, the semiconductor device is subjected to a heat treatment (it is called as a reflow stop). The circuit board has radiation pads located in corresponding position to the radiation solder bumps and connection pads located in corresponding position to the connection solder bumps. The radiation solder bumps and connection solder bumps are malted by the heat treatment so that both of the solder bumps are connected and joined to the pads, respectively. Therefore, the semiconductor device is fixed on the circuit board.

Each of the connection solder bumps should be connected to one of the connection pads independently. Therefore, the connection solder bumps are formed with a predetermined pitch so that the adjacent connection solder bumps should not joined each other by the heat treatment (it is called as a solder bridge).

The radiation bumps which are not connected to the electrodes of the semiconductor chip are formed with the same pitch of the connection solder bumps. The heat energy generated by the semiconductor chip in the package is transferred to the circuit board through a thermal conduction part including the radiation bumps and radiation pads. The transferred heat energy is diffused in the circuit board and outgoing from the circuit board.

Since the radiation solder bumps are formed with the same pitch of the connection solder bumps, a cross sectional area of the thermal conduction part is relatively small and a coefficient of thermal conductivity thereof is low.

SUMMARY OF THE INVENTION

The present invention is done in consideration of the problems of the conventional semiconductor device. The object of the present invention is to provide a now and improved semiconductor device including protruding radiation electrodes which improve the thermal conductivity coefficient of the semiconductor device.

To solve the issues of the conventional semiconductor device, a package structure for a semiconductor device comprises a substrate having a main surface and a back surface, a semiconductor chip formed on the main surface of the substrate, a package covering the semiconductor chip, protruding radiation electrodes and protruding connection electrodes. The protruding radiation electrodes are formed on the back surface of the substrate in a chip area where the semiconductor chip is located. Each of the protruding radiation electrodes are formed with a first pitch so that the protruding radiation electrodes make one body joining layer when the package structure is subjected to heating treatment. The protruding connection electrodes are formed on the back surface of the substrate in a peripheral area of the protruding chip area. Each of the connection electrodes formed with a second pitch which is larger than the protruding first pitch so that the connection electrodes remain separated when the package structure is subjected to a heat treatment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment is described referring toFIGS. 1 through 6.FIG. 1is a side elevation view of a semiconductor device according to the first embodiment of the present invention. A semiconductor device10according to the first embodiment of the present invention includes a package11in which a semiconductor chip (not shown inFIG. 1) is molded. The semiconductor device10includes a substrate11ahaving a main surface on which the package11and the semiconductor chip are formed. The semiconductor device10further includes radiation solder bumps13and connection solder bumps14formed on a back surface of the substrate11a.

As shown inFIG. 2, the radiation solder bumps13are located in the central region of the back surface of the substrate11a. Surrounding the central region is an intermediate region in which no solder bumps are located. The connection solder bumps14are located in a peripheral region which surrounds the intermediate region of the back surface of the substrate11a.The connection solder bumps14are electrically connected to electrodes of the semiconductor chip through conductive lines formed in the substrate, respectively. Therefore the connection solder bumps14function as terminals for connecting the semiconductor device to an outside surface.

When the semiconductor device10is mounted on a circuit board, first, the semiconductor device10is put on the circuit board20. The circuit board20has radiation pads21located in corresponding position to the radiation solder bumps13as shown inFIG. 5. The circuit board20further has connection pads22located in corresponding position to the connection solder bumps14as shown inFIG. 6. Then, the semiconductor device and the circuit board are subjected to a heat treatment (reflow step). The radiation solder bumps13and connection solder bumps14are melted by the heat treatment so that both of the solder bumps13,14are connected and joined to the radiation pads21and the connection pads22, respectively. Therefore, the semiconductor device10is fixed on the circuit board20.

Since each of the connection solder bumps14is connected to one of the electrodes of the semiconductor chip, the connection solder bumps14should be connected to the connection pads22individually. Therefore, as shown inFIGS. 1 and 2, the connection solder bumps are located with a predetermined pitch or distance so that the adjacent connection bumps14should not joined together by the heat treatment (the joining of bumps is called as a solder bridge).FIGS. 1 and 2also show that the width of the intermediate region is greater than the distance between the connection solder bumps14.

On the other hand, the radiation solder bumps13are located with a smaller pitch or distance than that of the connection solder bumps' as shown inFIGS. 1 and 2. Therefore, the radiation solder bumps13are joined together to form a solder bridge by the heat treatment, as a result, the radiation bumps form a one body connection layer30as shown inFIG. 3. In the first embodiment, the connection layer30for an outgoing radiation is connected to the individual radiation pads21.

For example, diameter of the radiation solder bumps13and the connection solder bumps14is 0.75 mm, the pitch or distance between the radiation solder bumps13is 1.00 mm and the pitch or distance between the connection solder bumps13is 1.27 mm. Preferably, the pitch or distance between the radiation solder bumps13is 1 to 1.4 times greater than the diameter of the radiation solder bumps13. Also, the pitch or distance between the connection solder bumps14is 1.6 to 1.7 times greater than the diameter of the connection solder bumps14.

In the structure shown inFIG. 3, heat energy generated in the semiconductor chip during the operation is transferred to the circuit board20through the connection layer30. The transferred heat energy is diffused in the circuit board20and outgoing from the circuit board20. At this time, since a thermal conduction part from the semiconductor device10to the circuit board20is comprised of a joining connection layer30, an effective area ratio for outgoing radiation is higher than that of the conventional semiconductor device structure. Therefore, radiation efficiency of the semiconductor device according to the first embodiment of the present invention is improved.

For the purpose of joining the adjacent radiation solder bumps13easily, a ratio of the effective area of the radiation pads21to all area thereof should be higher than a ratio of the effective area of the connection pads22to all area thereof. For example, as shown inFIGS. 5 and 6, a solder resist layer40having openings41and42are formed on the surface of the circuit board20. In such case, the opening41for the radiation pad21should have larger diameter d2(shown inFIG. 5) than a diameter d1of the opening42for the connection pad22as shown inFIG. 6.

The diameter d1of the opening42for the connection pads22, that is an effective area ratio, is determined so that the adjacent connection solder bumps are not joined to each other. On the other hand, the effective area ratio for the radiation pads21is set to higher than that for the connection pads22so as to form the solder bridge easily. Where the diameter of the opening41is relatively bigger, the diameter of the radiation bumps13can be bigger and the solder bridge is easily formed.

FIG. 7is a side elevation view of a semiconductor device and a circuit board according to the second embodiment of the present invention.FIG. 8is a bottom plan view of the semiconductor device according to the second embodiment of the present invention.FIG. 9is an enlarged elevation view of the semiconductor device and the circuit board shown in dotted square inFIG. 7. In the second embodiment, the semiconductor10has the same structure of the first embodiment. The circuit board20of the second embodiment has a radiation pad23having a wide continued area covering the central area of the back surface of the substrate11a.

In the second embodiment, the connection layer30of the semiconductor device10is joined with the radiation pads entirely. Therefore, thermal conduction efficiency between the connection layer30and the circuit board20is larger than that of the first embodiment. So, the heat energy generated in the semiconductor chip is transferred to the circuit board effectively.

FIG. 10is a sectional view of a semiconductor device50according to the third embodiment of the present invention. In the third embodiment, a substrate51ahas a radiation board53in the central area on the back side thereof. The radiation board has a high thermal conductivity coefficient for transferring heat energy from a semiconductor chip52molded by the package51to radiation solder bumps54which are formed on the radiation board53. The connection solder bumps are formed in the peripheral area of the substrate51a. Bonding wires56connect the electrodes of the semiconductor chip52and the conductive lines formed in the substrate51a, respectively. As explained in the first embodiment, each of the conductive lines is connected to the connection solder bumps55, respectively. The pitches or distances between the radiation solder bumps54and between the connection solder bumps55are the same as in the first embodiment.

In the third embodiment, the heat energy generated in the semiconductor chip52is effectively transferred to the radiation solder bumps54through the radiation board53. When the radiation solder bumps54are turned to the connection layer by the heat treatment and the connection layer is connected to the circuit board, higher radiation efficiency than that of the first embodiment is obtained.

FIG. 11is a sectional view of a semiconductor device50according to the fourth embodiment of the present invention. The semiconductor device50of the fourth embodiment further includes a transit portion53ain addition to the semiconductor device of the third embodiment. The transit portion53adirectly contacts to a semiconductor chip52and a radiation board53. The transit portion53ais formed of a material having high coefficient of thermal conductivity coefficient. Other portions of the fourth embodiment are the same as in the third embodiment.

In the fourth embodiment the energy generated in the semiconductor chip52is transferred to the radiation board53through the transit portion53a. Therefore, higher radiation efficiency than that of the third embodiment is obtained.

FIG. 12is a sectional view of a semiconductor device50according to the fifth embodiment of the present invention. The semiconductor device50of the fifth embodiment has a plane transit portion53binstead of the transit portion53aof the fourth embodiment. The piano transit portion53bdirectly contacts a semiconductor chip52and a radiation board53. The plane transit portion53bis formed of a material having high thermal conductivity coefficient of other portions of the fifth embodiment the same as in the fourth embodiment.

In the fourth embodiment, the energy generated in the semiconductor chip52is transferred to the radiation board53through the plane transit portion63b. Since the plane transit portion53bcontacts to the semiconductor chip52and the radiation board53with larger area than the transit portion53a, higher radiation efficiency than that of the fourth embodiment is obtained.

Further, the semiconductor chip52can directly contact the radiation board53without the transit portion53bin this case, the semiconductor chip52is joined with the radiation board53by die bonding material.

FIG. 13is a sectional view of a semiconductor device60according to the sixth embodiment of the present invention. In the sixth embodiment, the semiconductor device60has a substrate62having a recess on the back surface62athereof. The semiconductor chip61is mounted in the recess of the substrate62by the chip-on board mounting (COB) method so that electrodes of the semiconductor chip are connected to conductive lines (not shown inFIG. 13) formed in the substrate62. Radiation solder bumps63are formed on the back surface of the semiconductor chip61directly. Connection solder bumps64are formed on the back surface62aof the substrate62in order to be connected to the conductive lines, respectively. The pitches or distances between the radiation solder bumps63and between the connection solder bumps64are the same to the first embodiment.

In the sixth embodiment, the heat energy generated in the semiconductor chip61is directly transferred to the radiation solder bumps63.

FIG. 14is a sectional view of the semiconductor device according to the is seventh embodiment of the present invention. In the seventh embodiment, a peripheral area of the substrate62and connection solder bumps have the same structure of the sixth embodiment. Therefore, explanation of these portions are omitted from the drawing (FIG. 14) and the specification.

In the seventh embodiment, a solder resist layer65having openings66is formed on the back surface of the semiconductor61and the back surface62aof the substrate62. The opening are located to the corresponding positions for the radiation solder bumps63(located on the back surface of the semiconductor ship61) and for the connection solder bumps (not shown; located in the peripheral area of the back surface62aof the substrate62). As shown inFIG. 14, the radiation solder bumps63are formed at the designed position which is led from the opening66. The radiation solder bumps63are positioned closely each other for joining in one body during the heat treatment. Where the position of the radiation solder bumps63is deviated from the designed position, the solder bumps63are joined before the heat treatment. In such case, a height of the joined radiation solder bumps63turns low and such bumps may not contact the circuit board. However, in the seventh embodiment, the radiation solder bumps63are formed at the position of the opening66of the solder resist layer65so that the radiation solder bumps63are formed in the designed positions and the radiation solder bumps63have the same height. Therefore, the radiation solder bumps63of the seventh embodiment can contact the circuit board surely.

As explained above, according to the present invention, the semiconductor device has radiation protrude electrodes joining to one body connection layer by the heat treatment. Therefore, effective area for outgoing radiation is increased and radiation efficiency is improved.