A semiconductor device using a lead frame and its manufacturing method

Abstract: A semiconductor device comprises a lead frame (53) formed of a conductive material, a semiconductor chip (11) having an electrode (14) on its surface, a first connection section (54) where the lead frame is electrically connected to an electrode on the semiconductor chip by a conductive adhesive; and a second connection section (55) where the lead frame is electrically connected to said electrode on said semiconductor chip by a metal plating to cover the surroundings of said first connection section (54). This structure enhances the connection of the lead frame and the pad electrode of the semiconductor chip.

Description: The present invention relates to a semiconductor device, in which an electrical connection between electrodes on a semiconductor chip and inner leads of a lead frame is provided and an electrical connection between outer leads of the lead frame and wiring patterns on a print circuit board is provided, and its manufacturing method, and more particularly to a semiconductor device wherein a distance between electrodes on the semiconductor chip to provide the electrical connection and a distance between the inner leads of the lead frame and a distance between the outer leads thereof are minute, and its manufacturing method. When the semiconductor device is manufactured, there are numerous portions where an electrical connection is to be provided such as a portion between an electrical pad on a semiconductor chip and an inner lead of a lead frame, and a portion between an outer lead of the lead frame and a wiring pattern on a print circuit board. Conventionally, for example, the electrical connection between the electrode pad on the semiconductor chip and the inner lead is made by a metal bonding such as a wire bonding using AU wire or Aℓ wire, a TAB (Tape Automated Bonding) method, an ohmic contact such as a metal contact between a bump electrode on a flip chip and a lead, and the like. Regarding the connection by the wiring bonding, the shortest distance between adjacent wires is restricted by the outer shape of a bonding capillary to be used. Due to this, it is difficult to reduce the distance between the pads on the semiconductor chip to be about 100 µm. Moreover, in order to connect an Au ball or an Aℓ wire to an aluminum pad on the semiconductor chip, it is necessary to apply a physical load such as heating, pressing, ultrasonic vibration. Therefore, damage is often applied to the semiconductor chip itself under the electrode pad. In a case where TAB system or the flip chip is used, it is necessary to metal-connect Au bump or plating bump to the inner lead. Due to this, the temperature of the above case often increases higher than that of the wire bonding connection, so that a physical damage due to pressure remains. In this case, the distance between the pads can be reduced to about 80 µm, however, there is a limitation in the reduction of the bump size because of the use of the metal connection. Moreover, a large number of portions are connected at the same time. Due to this, as the number of portions to be connected is increased more, it is more difficult to obtain a stable connection in view of the height of the bump, and the condition of the connection. Due to this, it is required that the process conditions be stabilized. The above-mentioned problem occurs in not only the electrical connection between the pad on the semiconductor chip or the bump and the inner lead but also the electrical connection between the outer lead and the wiring pattern on the print circuit board. An object of the present invention is to provide a semiconductor device, in which the distances between portions to be electrically connected can be reduced more than the conventional case and high reliance can be obtained without applying physical damages due to heating, pressurizing when the electrical connection is made, and its manufacturing method. In JP-A-01207938 there is disclosed a method of connecting leads to electrode pads of semiconductor chips which involves the use of conductive paste disposed in apertures of insulating film carriers for the leads, which apertures are aligned with the electrodes. In JP-A-02121359 there is described the improvement of the connection between a lead and a conductor circuit in bonding strength and electrical reliability by a method in which a plating layer is formed on the surface of a lead, an electrically conductive bonding agent and a conductor circuit. According to the present invention, there is provided a semiconductor device comprising: a) a lead frame formed of a conductive material and having at least one lead; b) a semiconductor chip having at least one electrode on its surface; and wherein each said lead is electrically connected to a respective electrode by a conductive adhesive, characterized by c) a respective first connection section whereby each said lead of the lead frame is electrically connected to said respective electrode on the semiconductor chip by the conductive adhesive; and d) a respective second connection section whereby each said lead is electrically connected to said respective electrode on said semiconductor chip by a metal plating covering and surrounding the respective first connection section and extending to and contacting both said electrode and said lead. Moreover, according to the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps: a) forming a conductive adhesive as a respective first connection section on each of a plurality of electrodes of a semiconductor chip by a screen printing method, b) adhering each electrode to a respective lead of a lead frame, formed of a conductive material, by means of the respective first connection section, and c) forming a metal plating layer as a respective second connection section surrounding each first connection section, the plating layer electrically connecting each electrode and the respective lead and extending to and contacting both said electrode and said lead. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a cross sectional view showing the structure of a part of a device which is not in accordance with the present invention; Fig. 2 is a cross sectional view showing a general structure of the device of Fig. 1; Fig. 3 is a cross sectional view showing a specific structure of an electrode pad of the device of Fig. 1; Fig. 4 is a plane view showing a state of the connection between a plurality of electrode pads of the device of Fig. 1 and a plurality of inner leads; Figs. 5 and 6 are plane views of a TAB tape, which is used in the device of Fig. 1, respectively; Figs. 7 and 8 are plane views of modifications of the device of Fig. 1, respectively; Fig. 9 is a cross sectional view showing another device which is not in accordance with the present invention; and Fig. 10 is a cross sectional view showing a device according to an embodiment of the present invention. An embodiment of the present invention will now be explained with reference to the drawings of which Figs. 1-9 are not in accordance with the present invention, but which are useful in facilitating understanding thereof. Fig. 1 shows the structure of a part of a semiconductor device and the connection between a plurality of electrode pads on a semiconductor chip and a plurality of inner leads, and Fig. 2 is the general structure thereof. In the drawings, reference numeral 11 is a semiconductor chip wherein is an active element such as a transistor and a passive element such as a resistor and a capacitor. Around the main surface of the semiconductor chip 11, there are formed a plurality of electrode pads 14, which are formed of a first metal layer 12 whose lower layer is formed of aluminum (Aℓ) and a second metal layer 13 whose upper layer includes at least one nickel layer. These electrode pads 14 are arranged in line with a predetermined distance. The portions of the semiconductor chip 11 other than the electrode pad formation position are covered with an insulating surface protection film 15 such as a silicon oxidation film. The semiconductor chip 11 is adhered to a predetermined portion of a TAB tape 17 by an epoxy adhesive 16. As shown in Fig. 1, the TAB tape 17 is made of epoxy or polyimide resin. Metal foil such as copper (Cu) foil having a thickness of about 35 µm is laminated on an organic film material 18 having a thickness of about 75 µm. Thereafter, there is formed a wiring pattern comprising a plurality of inner leads 19 to be connected to the plurality of electrode pads 14 by a selection etching technique and outer leads electrically connected to these inner leads (not shown). The wiring pattern forming surface is adhered to the semiconductor chip 11 by the adhesive 16. When the semiconductor chip 11 is adhered to the TAB tape 17, the positioning is performed in a state that each electrode pad 14 is positioned close to the portion where each end surface of the end portions of the plurality of inner leads 19 is exposed. Then, each electrode pad 14 on the semiconductor chip 11 and each end portion of the inner lead 19 are electrically connected through a metal plating layer 20 formed of nickel (Ni). Fig. 3 shows the specific structure of each electrode pad 14. The second metal layer 13 formed on the first metal layer 12 made of aluminum (Aℓ) comprises at least two metal layers. More specifically, the lower layer contacting the first metal layer made of aluminum is formed of a titanium (Ti) layer 31 having a thickness of 100 nm (1000 Å), and the upper layer is formed of the nickel (Ni) layer 32 having a thickness of 300 nm (3000 Å). The nickel layer 32, which is the upper layer of the second metal layer 13 is formed to allow the metal plating layer 20 made of nickel to be formed on the electrode pad 14. Also, the titanium layer 31, which is the lower layer of the second metal layer 13, has a function as barrier metal. Fig. 4 shows a state of the connection between the plurality of electrode pads 14 and the plurality of inner leads 19 formed on the TAB tape 17. In the drawing, a region in which slant lines are added shows the metal plating layer 20. Each electrode pad 14 on the semiconductor chip 11 and each inner lead 19 are connected by the metal plating layer 20. Due to this, bonding capillary and TAB tool, which are used to make the wire bonding and TAB connection are not required. Thereby, the distance between electrode pads 14 can be reduced to 100 µm or less, for example, about 50 µm. Moreover, if each electrode pad 14 and each inner lead 19 are electrically connected in this way, no physical pressure is applied to the semiconductor chip 11, so that reliance due to pressure damage is not lowered. Then, since a large number of portions can be connected at the same time under the same condition, reliance of connection can be improved. Moreover, since there is no need of heating when the connection is performed, it is possible to prevent reliance from being lowered by thermal stress, which is caused by a mismatch of the coefficient of thermal expansion of each semiconductor layer in the semiconductor chip. A method of forming the above metal plating layer where the electrode pads and the inner leads are electrically connected will now be explained. In TAB tape, as shown in Fig. 5, metal foil such copper foil is laminated on the organic film material 18 in advance. Thereafter, for every semiconductor device, there are formed a plurality of lead electrodes 41 comprising the inner leads and the outer leads connected to the inner leads by the selection etching technique. At the same time when the selection etching is performed, common electrodes 42, which are electrically connected to the lead electrodes 41, are formed around each semiconductor device in a state that all common electrodes 42 are connected. Additionally, in Fig. 5, reference numeral 43 is an opening formed in the organic film material 18. Fig. 6 shows an enlarged view of one semiconductor device in the TAB tape of Fig. 5 In the drawing, the semiconductor chip is adhered to TAB tape in a state that the semiconductor chip is positioned in the area shown by a one dotted chain line. In this case, the semiconductor chip is adhered to TAB tape so that the pad of each electrode on the semiconductor chip is positioned close to the portion where each end of the end portion of the plurality of leads is exposed. Thereafter, TAB tape is immersed in a nickel plating bath together with a plating electrode. The nickel plating bath is generally called a watt bath, and nickel sulfate, nickel chloride, and adhesive are used. After TAB tape and the plating electrode are immersed in the watt bath, a predetermined direct voltage is applied between the common electrode 42 and the plating electrode in order that the common electrode 42 serves as a positive side and the plating electrode serves as a negative side, and electrolytic plating is performed for a predetermined period of time. For example, a direct voltage to be applied was set to 2V, a current to be supplied between the positive and negative sides was set to 60mA, and plating time was set to 10 minutes. As a result, a nickel plating layer having a thickness of 10 µm was obtained as metal plating layer 20. The metal plating layer grows from each end surface of the top end portion of the inner lead immediately after plating starts. Then, if the growth advances and the plating layer contacts the electrode pad on the semiconductor chip, the metal layer also grows in the electrode pad, and both the common electrode 42 and the plating electrode are finally electrically connected by the plating layer. After the end of plating, the plating layer is washed with pure water, and contaminant, which was adhered to the surface when plating, is removed. Additionally, in the surface of each lead electrode 41, which comprises the inner and outer leads, the most of the surface other than the top end portion of the inner lead is coated with an epoxy insulating film, which is called green coat. Thereby, it is possible to form the plating layer in only the necessary portion. Due to this, plating time can be shortened. In the above the electrode pads were arranged in line with a predetermined distance. In the modified device of Fig. 7., the electrode pads 14 are arranged on the semiconductor chip in a zig-zag manner. The same reference numerals as Fig. 4 are added in the portions corresponding to the portions of Fig. 4, and the explanation thereof is omitted. Fig. 8 shows a modification of the device using a semiconductor which is the so-called free access pad layout system wherein the electrode pads are arranged on the entire surface of the semiconductor chip at random. As mentioned above, the described connection method can be used in any type of chip regardless of the arrangement of the electrode pads on the chip. Fig. 9 shows the structure of another semiconductor device which is not in accordance with the present invention and where the connection is between outer leads of the lead frame and the wiring pattern on a print circuit board. In the drawing, reference numeral 11 is a semiconductor chip, and reference numeral 17 is a TAB tape. The top end portion of the inner lead of the TAB tape and electrode pad (not shown) on the semiconductor chip 11 are electrically connected by a metal plating layer 20 similar to that described above. A wiring pattern 52, which is formed on a print circuit board 51, and the outer lead of the TAB tape are also electrically connected by the metal plating layer 20. An embodiment of the present invention will now be described with reference to Fig. 10 which shows the structure of the semiconductor device and the connection between the inner leads of the lead frame and the electrode pads of the semiconductor chip. According to the embodiment, the lead frame is formed by punching a metal thin film, which is formed of alloy such as 4-2 alloy and copper by a press process. An inner lead 53 of the lead frame and an electrode pad 14 on a semiconductor chip are electrically connected by use of both a conductive adhesive 54 and a metal plating layer 55. In the case of the above described device using the TAB tape, the metal plating layer can be formed in a manner that the semiconductor chip is adhered to the TAB tape by the epoxy adhesive in advance. In the Fig. 10 case of using the lead frame formed by punching the metal thin film, the conductive adhesive 54 is formed on each electrode pad 14 in advance by a screen printing method, and the electrode pad 14 and the lead frame 53 are adhered by the conductive adhesive 54. Thereafter, the plating layer 55 is formed by the same method as mentioned above, and both the electrode pad and the lead frame can be electrically connected. The present invention is not limited to the above-mentioned embodiment It is needless to say that the present invention can be variously modified. For example, in the above it was explained the case wherein the metal plating layer was the nickel plating layer. According to the present invention, Au plating layer and copper plating layer can be used in addition to the above case. In the above it was explained the case wherein the most of the surface other than the top end portion of the inner lead was coated with the insulating film in advance. However, in the portion other than the top end portion of the inner lead, the thickness of which the plating layer can grow on the above portion is about only 1/10 times that of the top end portion when the electrolytic plating is performed, the adherence of the insulating film can be omitted. Moreover, the method explained the case that the plating layer was formed by the electrolytic plating method. However, the plating layer can be formed by an electrolessly plating method.

Claims: Semiconductor device, comprising: a) a lead frame formed of a conductive material and having at least one lead (53); b) a semiconductor chip (11) having at least one electrode (14) on its surface; and wherein each said lead is electrically connected to a respective, electrode said electrical connection containing c) a first connection section (54) whereby each said lead (53) of the lead frame is electrically connected to said respective electrode (14) on the semiconductor chip by a conductive adhesive; and said electrical connection characterised by d) a second connection section (55) whereby each said lead (53) is electrically connected to said respective electrode (14) on said semiconductor chip by a metal plating covering and surrounding the first connection section (54) and extending to and contacting both said electrode and said lead. Semiconductor device according to claim 1, characterized in that said lead frame (53) is comprised by a punched metal film. Semiconductor device according to claim 1, characterized in that there are a plurality of said electrodes (14) formed on the surface of the semiconductor chip and each comprises an aluminium layer (12), a titanium layer (31) formed on said aluminium layer (12), and a metal layer (32) formed on the titanium layer, the metal layer comprising a nickel layer or a copper layer. Semiconductor device according to claim 1, characterized in that there are a plurality of said electrodes arranged on the semiconductor chip in a zig-zag manner. Semiconductor device according to claim 1, characterized in that there are a plurality of said electrodes arranged on the semiconductor chip at random. Semiconductor device according to claim 1, characterized in that the metal plating second connection (55) contacts one end portion of said lead (53) said end portion being directly adjacent to said respective electrode (14). Method of manufacturing a semiconductor device, comprising the steps: a) forming a conductive adhesive as a first connection section (54) on each of a plurality of electrodes (14) of a semiconductor chip by a screen printing method, b) adhering each electrode (14) to a respective lead (53) of a lead frame, formed of a conductive material, by means of said first connection section (54), and c) forming a metal plating layer as a second connection section (55) surrounding each first connection section (54), the plating layer electrically connecting each electrode (14) and the respective lead and extending to and contacting both said electrode and said lead. Method of manufacturing a semiconductor device according to claim 7, characterized in that step c) of comprises the steps of : a) immersing the lead frame and the semiconductor chip in an electrolytic plating solution, and b) forming the metal plating layer. Method of manufacturing a semiconductor device according to claim 8, characterized in that the lead frame frame has a plurality of lead electrodes (41), the plurality of lead electrodes (41) are electrically connected by a common electrode (42), and an electric potential is supplied to the common electrode (42) when the metal plating layer is formed.

Inventors: FUJITSU TAKAO, FUJITSU, TAKAO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: H01L21
IPC codes: H01L23, H01L21