Electronic circuit device and method of production of the same

An electronic circuit device of a three-dimensional mounting mode capable of being produced by a simple method while suppressing the production costs and of a structure resistant to external stress, including first-mounting-board wiring portions formed on a first mounting board, first mounting parts mounted on the first mounting board, bumps formed on the first mounting board connecting to the first-mounting-board wiring portion, a protective layer formed covering the first mounting parts so that at least the portions near the tops of the bumps are exposed, a second mounting board stacked as an upper layer of the protective layer, second-mounting-board wiring portions formed on the second mounting board in order to connect to the bumps, and second mounting parts mounted connecting to the second-mounting-board wiring portions on the second mounting board at the surface of the second mounting board opposite to the protective layer side, and a method of production of the same.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, preferred embodiments of an electronic circuit device and the method of production of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional view of an electronic circuit device according to the present embodiment. Buried wiring 11 is formed inside a first mounting board 10 , while surface wirings ( 12 , 13 ) are formed on the two sides of the first mounting board 10 . Here, the surface wiring includes test terminals 12 ′ for confirming connection of mounting parts. Also, through holes are formed penetrating through the first mounting board 10 . Further, through hole wiring 14 and through hole electrodes ( 15 , 16 ) connected thereto are formed. As explained above, a first-mounting-board wiring portion is comprised by the buried wiring 11 , surface wiring ( 12 , 13 ), through hole wiring 14 , and through hole electrodes ( 15 , 16 ) and so on. A semiconductor chip (first mounting part) 20 connected to the surface wiring 12 etc. formed on one surface of the first mounting board 10 is mounted connected via the bumps 21 composed of solder etc. The space between the semiconductor chip 20 and the first mounting board 10 is sealed by a sealing resin layer 22 . Furthermore, bumps 23 composed of solder are formed connecting to the through hole electrodes 15 etc. formed on one surface of the first mounting board 10 . The bumps 23 are formed so that they become higher in height than that after mounting the semiconductor chip 20 . Here, a protective layer 24 of a sealing resin layer etc. Is formed by covering the semiconductor chip 20 so that at least the portions near the tops of the bumps 23 are exposed. An anisotropic conductive layer 25 such as an anisotropic conductive film or an anisotropic conductive paste is stacked as an upper layer of the protective layer 24 . The second mounting board 30 is stacked thereon. Here, the anisotropic conductive film is comprised of an insulating resin in which fine conductive balls are dispersed and processed to a film shape. The film itself is insulating but when it is squeezed by being sandwiched between a pair of electrodes, the conductive balls contact the pair of electrodes and electrically connect and bond the two electrodes. The anisotropic conductive paste is a paste of an insulating resin in which fine conductive balls are dispersed. An anisotropic conductive film formed by applying the paste has the same effect as the above anisotropic conductive film. A second-mounting-board wiring portion is formed by surface wiring 31 formed on one or both surfaces of the second mounting board 30 , through hole wiring 32 passed through the through holes formed penetrating through the second mounting board 30 , through hole electrodes ( 33 , 34 ) connected thereto, etc. The through hole electrode 33 etc. at the second-board wiring portion squeezes the anisotropic conductive layer 25 such as an anisotropic conductive film or anisotropic conductive paste and connects to the bumps 23 via the conductive balls in the anisotropic conductive layer 25 . Furthermore, on the second mounting board 30 at the surface of the second mounting board 30 opposite to the protective layer 24 are mounted as the second mounting parts, a semiconductor chip 35 via the bumps 36 composed of solder etc., or resistors, capacitors, or other general electronic parts 37 directly connecting to the surface wiring 31 of the second-mounting-wiring portion etc. The above electronic circuit device of the present embodiment is an electronic circuit device of a three-dimensional mounting mode having a configuration resistant to stress from the outside and ensuring reliability of high packing density. The configuration does not require a board formed with openings in advance and can be produced by a simple method suppressing production costs. The three-dimensional mounting mode enables to layout by wiring of the shortest connection wiring length and to realize a mounting mode applicable to a high speed and high frequency due to reduction of wiring resistance 15 loss. Next, a method of production of the electronic circuit device according to the above present embodiment will be explained with reference to the drawings. First, as shown in FIG. 2 A, the first mounting board formed with buried wiring 11 therein. On both surfaces of the first mounting board 10 are formed surface wirings ( 12 , 13 ) including test terminals 12 ′ for confirming connection of mounting parts. Furthermore, through holes are formed penetrating through the first mounting board 10 . Through hole wiring 14 and through hole electrodes ( 15 , 16 ) connecting thereto are formed. As explained above, a first-mounting-board wiring portion comprised of the buried wiring 11 , surface wiring ( 12 , 13 ), through hole wiring 14 , and through hole electrodes ( 15 , 16 ) etc. is formed. Next, as shown in FIG. 2B, a semiconductor chip (first mounting part) 20 formed with bumps 21 composed of solder etc. are mounted connecting to the surface wiring 12 etc. formed on one surface of the above first mounting board 10 . By making the thickness of the above semiconductor chip 20 thinner to the limit, the thickness of the overall board can be suppressed even when the semiconductor chip is buried. For example, by making the thickness of the semiconductor chip not more than 0.1 mm, the height of the semiconductor chip after mounting can be suppressed to be not more than 0.2 mm. At this time, when examining connection conditions of semiconductor chips 20 by using test terminals 12 ′ for confirming the connection of the mounting parts and confirming poor connection, it is possible to exchange poor semiconductor chips 20 and thereby mount only good chips. Next, as shown in FIG. 2 C, by filling a resin in a space between the semiconductor chip 20 and the first mounting board 10 by a not shown dispenser etc. and applying annealing or other curing treatment, a sealing resin layer 22 is formed. By forming the sealing resin layer 22 , the reliability of connection of a semiconductor chip 20 can be improved. Next, as shown in FIG. 2 D, bumps 23 are formed connecting to the through hole electrode 15 etc. formed on one surface of the first mounting board by transfer of solder balls etc. Here, the height HI of the bumps 23 is set to be higher than the height H 2 of a semiconductor chip 20 after mounting, for example, when the height H 2 of the semiconductor chip 20 after mounting is not more than 0.2 mm, solder balls etc. having a diameter of 0.25 to 0.3 mm are used. Next, as shown in FIG. 2 E, by supplying an epoxy resin etc. to cover the semiconductor chip 20 and the bumps 23 by for example a printing method, a protective layer 24 for sealing the semiconductor chip 20 etc. with resin is formed. At this time, a somewhat larger quantity of epoxy resin is supplied, excess resin is removed by a squeegee S, and heat treatment of for example 150 to 200° C. is performed for curing. By using the above protective layer to seal with resin the semiconductor circuit device and the base portion of the bumps 23 , the reliability of connection of the semiconductor chip 20 and the bumps 23 can be improved. Next, as shown in FIG. 2 F, the protective layer 24 is polished until at least the portions near the tops of the bumps are exposed. From the above, the protective layer 24 can be formed covering the first mounting part so that at least the portions near the tops of the bumps are exposed while securing the flatness of the protective layer 24 . Next, as shown in FIG. 2 G, for example, an anisotropic conductive film 25 such as an anisotropic conductive film or anisotropic conductive paste is stacked as an upper layer of the protective layer 24 and a second mounting board 30 is further stacked thereon. Here, on the second mounting board 30 , a second-mounting-board wiring portion comprised by surface wiring 31 formed on one or both surfaces of the second mounting board 30 , through hole wiring 32 passed through the through holes formed penetrating through the second mounting board 30 , through hole electrodes ( 33 , 34 ) connected thereto, etc. is formed arranged to be in register with the positions of the bumps 23 . By crushing and heat bonding the anisotropic conductive layer 25 such as the anisotropic conductive film or anisotropic conductive paste, the through hole electrodes 33 etc. of the second-mounting-board wiring portion and the bumps 23 are connected via the conductive balls in the anisotropic conductive layer 25 and the second mounting board 30 is adhered by the anisotropic conductive film 25 . As a result, the first-mounting-board wiring portion of the first mounting board and the second-mounting-board wiring portion of the second mounting board 30 are connected. Next, as shown in FIG. 2H, a semiconductor chip 35 formed with bumps 36 composed of solder etc. or resistors, capacitors, or other general electronic parts 37 are mounted as the second mounting parts on the second mounting board 30 at the surface of the second mounting board 30 opposite to the protective layer 24 side connected to the surface wiring 31 etc. of the second-mounting-board wiring portion. Next, resin is supplied to a space between the semiconductor chip 35 and the second mounting board 30 or a space between the general electronic parts 37 etc. and the second mounting board 30 by a not shown dispenser etc. Annealing or other curing is performed to form the sealing resin layer 38 and complete the electronic circuit device shown in FIG. 1 . As the method of forming the above bumps 23 , for example, a metal jet method shown in FIGS. 3A to 3 C may be used. In the above method, for example as shown in FIG. 3 A, solder 53 heated by a heater 50 to make it molten is stored in a solder dropper 52 with a built-in heater 50 and piezoelectric oscillator 51 . By causing the piazo oscillator 51 to oscillator at this time, drops of molten solder 54 drop from the tip of the solder dropper 52 to the electrodes 56 on the board 55 . The molten solder drops 54 cool as they drop and hardened on the electrodes 56 to form bumps 57 . Here, by continuously dropping the molten solder drops 54 as shown in FIG. 3 A, the molten solder drops 54 pile up as shown in FIG. 3B so that finally a solder bump 57 having a small diameter and a high aspect ratio can be formed as shown in FIG. 3C . According to the method of production of the electronic circuit device of the present embodiment, a board formed with openings in advance is not necessary and it is possible to produce an electronic circuit device of a three-dimensional mounting mode having a configuration resistant to stress from the outside and ensuring the reliability of high density mounting can be produced by a simple method while suppressing the production costs. The mounting part to be mounted on the electronic circuit device of the present invention may be of any kind such as an MOS transistor type semiconductor device, a bipolar type semiconductor device, BiCMOS type semiconductor device, a semiconductor device mounting a logic and memory, etc. The electronic circuit device and the method of production of the present invention are not limited to the above embodiments. For example, as mounting parts buried in the protective layer between the first mounting board and the second mounting board, resistors, capacitors, and other general electronic parts can be mounted other than semiconductor chips. Also, the materials comprising the mounting boards, wiring layers, bumps, sealing resin, protective layers, etc. are not specifically limited. Materials other than those described in the above embodiments may be used. A variety of modifications can be made within the scope of the present invention. Summarizing the effect of the invention, as explained above, according to the present invention, there is provided an electronic circuit device of a three-dimensional mounting mode which does not require a board formed with openings in advance and able to be produced by a simple method while suppressing the production costs. Also, according to the method of production of the electronic circuit device of the present invention, an electronic circuit device of the present invention can be easily produced, a board formed with openings in advance is not necessary, and an electronic circuit device of a three-dimensional mounting mode configured to be resistant to stress from the outside can be produced by a simple method while suppressing the production costs. While the invention has been described with reference to specific embodiment chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.