Resin-sealed semiconductor device and method of manufacturing the device

Abstract: A resin-sealed semiconductor device according to this invention is an LOC type semiconductor device comprising a semiconductor chip (3) having a circuit surface on which an electrode is formed; a lead (1) which is arranged in such a manner that the distal end of the lead overlaps the semiconductor chip, and which is electrically connected to each electrode; a lead fixing resin layer (9) interposed between the semiconductor chip and the lead to fix them; and a sealing resin layer (2) coated to cover the semiconductor chip and the lead. The diameter of filler contained in the lead fixing resin layer is about 1/10 to 1/5 the diameter of filler contained in the sealing resin layer, and is about 1/10 a gap between the lead and the semiconductor chip.

Description: The present invention relates to a resin-sealed semiconductor device such as an IC or an LSI and a method of manufacturing the same. A resin-sealed semiconductor device comprises a semiconductor chip and a lead connected to the electrode of the semiconductor chip. The distal end of the lead and the semiconductor chip are sealed by a resin. The whole size of the resin-sealed semiconductor device including the sealing resin is determined by the standards. And generally, the size of the semiconductor chip increases as the degree of integration of the circuit increases. When the semiconductor chip increases in size and when the distal end of the lead is arranged not to overlap the semiconductor chip, length of a part of the lead fixed with the resin is shortened, and the lead cannot be rigidly fixed. Therefore, in this case, an LOC (Lead On Chip) type structure in which the distal end of the lead overlaps a semiconductor chip is generally employed. US patent 5,068,712 discloses a gap between the leading end portions of the inner leads and the semiconductor chip which is made wider than that between the inner lead portions except the leading end portions and the semiconductor chip thereby to reduce the stray capacity, to improve the signal transmission rate and to reduce the electrical noises in the package of structures called "Lead-On-Chip" or Chip-On-Lead". European patent application laid open No. 0 651 040 A1 refers to a liquid adhesive which can be adhered and cured at a relatively low temperature and has sufficient heat resistance and reliability as well as to a process for forming an insulation adhesive layer using the same. US patent No. 5,286,679 describes a method for attaching a semiconductor die to a leadframe comprising the forming of a patterned adhesive layer on a side of semiconductor wafer prior to singulation of the dies from the wafer. The adhesive layer is patterned such that wire bonding pads on the dies, as well as the streets between the dies, are free of adhesive material. US patent No. 5,300,459 discloses a method wherein a circuit substrate device is provided having a semiconductor element and a circuit substrate between which a protective resin is placed. The protective resin has a smaller coefficient of linear expansion than that of the circuit substrate and a greater coefficient of linear expansion than that of the semiconductor element. Japanese Patent Application Laid-Open No. 61-218139 discloses an LOC type resin-sealed semiconductor device. In the structure disclosed in this publication, as shown in FIG. 5, the distal end of a lead 1 is adhered to a semiconductor chip 3 through an insulating tape 4, and the distal end and an electrode 1b of the semiconductor chip 3 are connected to each other with a bonding wire 5. The semiconductor chip 3, the distal end of the lead 1, and the bonded portions are covered with the sealing resin layer 2. The sealing resin layer 2 generally consists of an epoxy-based resin whose ratio by weight is about 20% and filler whose ratio by weight is about 80%. The filler is silica-based solid bodies each having a diameter of 50 to 100 µm and has a function of keeping the hardness of a resin layer and a function of suppressing thermal expansion. However, since the above insulating tape 4 easily absorbs moisture, the moisture contained in the insulating tape 4 is steamed by heat generated in practical use. Force generated in this case disadvantageously makes cracks 6 in the sealing resin layer 2 as shown in FIG. 6. As shown in FIG. 7, if the large-diameter filler 7 is clogged in a gap of about 100 µm between the lead 1 and the semiconductor chip 3, stress is generated between the lead 1 and the semiconductor chip 3 when the sealing resin layer 2 is solidified. The stress is generated due to the difference between the coefficient of contraction of the sealing resin layer 2 and that of the filler 7. This stress may make flaws 8 such as cracks in the semiconductor chip 3. Summary of the Invention The present invention aims to solve the problems of the prior art described above, and its object is to provide a resin-sealed semiconductor device which employs an LOC type structure, suppresses formation of cracks in a sealing resin layer by heat in practical use, and can prevent flaws or cracks from being formed in a semiconductor chip in solidification of the sealing resin layer. The resin-sealed semiconductor device according to the present invention is defined in appended claim 1. A method of manufacturing a resin-sealed semiconductor device according to the present invention is defined in appended claim 5. Brief Description of the Drawings FIG. 1 is a partially sectional view of a resin-sealed semiconductor device according to an embodiment of the present invention; FIG. 2(A) is a side view of a semiconductor chip in the device shown in FIG. 1, and FIG. 2(B) is a plan view of the semiconductor chip in FIG. 2(A); FIG. 3(A) is a side view showing a state wherein a resin for a lead fixing resin layer is coated on the semiconductor chip in FIG. 2, and FIG. 3(B) is a plan view showing the state in FIG. 3(A); FIG. 4(A) is a side view showing a state wherein a lead is fixed to the semiconductor chip shown in FIG. 3, and FIG. 4(B) is a plan view showing the state in FIG. 4(A); FIG. 5 is a partially sectional view of a conventional resin-sealed semiconductor device; FIG. 6 is a partially sectional view showing a problem of the conventional resin-sealed semiconductor device; and FIG. 7 is a partially sectional view showing another problem of the resin-sealed semiconductor device. Detailed Description of the Preferred Embodiment An embodiment of a resin-sealed semiconductor device according to the present invention will be described below. A resin-sealed semiconductor device according to this embodiment, as shown in FIG. 1, is an LOC type semiconductor device comprising a semiconductor chip 3, a lead 1, a lead fixing resin layer 9 and a sealing resin layer 2. The semiconductor chip 3 is provided with a circuit surface 3a (serving as an upper surface in FIG. 1), and an electrode 10 is formed on the circuit surface 3a. The lead 1 is arranged at a predetermined gap with respect to the semiconductor chip 3 in such a manner that the distal end of the lead 1 overlaps the semiconductor chip 3. A bonding wire 5 electrically connects the distal end of the lead 1 and the electrode 10. The lead fixing resin layer 9 is filled between the semiconductor chip 3 and the lead 1 to fix the lead 1 to the semiconductor chip 3. The sealing resin layer 2 coated to cover the semiconductor chip 3 and the lead 1. The electrode 10 is formed on the semiconductor chip 3 such that a plurality of electrodes 10 are arranged in two lines at the central portion of the circuit surface 3a as shown in FIG. 2(A) serving as the side view and FIG. 2(B) serving as the plane view. The lead 1 connected to the electrodes 10 is formed such that a plurality of leads 1 are arranged in correspondence with the number of electrodes. The gap between the circuit surface 3a of the semiconductor chip 3 and the distal end of the lead 1 is about 40 to 100 µm. The lead fixing resin layer 9 is filled between the lead 1 and the circuit surface 3a over a range from the distal end of the lead 1 to the periphery of the semiconductor chip 3, i.e., a range in which the lead 1 overlaps the semiconductor chip 3. The sealing resin layer 2 contains filler having a diameter of 50 to 100 µm at a ratio by weight of about 80%, and the remaining 20% is an epoxy-based resin. On the other hand, the lead fixing resin layer 9 also consists of filler and an epoxy-based resin. However, the diameter of the filler is about 1/10 to 1/5 the diameter of the filler contained in the sealing resin layer 2, and is about 1/10 the gap between the lead 1 and the semiconductor chip 3 at the overlapping portion therebetween. The ratio by weight of the filler contained in the lead fixing resin layer 9 is set to be lower than the ratio by weight of the filler contained in the sealing resin layer 2. More specifically, the lead fixing resin layer 9 contains filler which has a diameter of about 10 µm and whose ratio by weight is about 40%, and the remaining 60% consists of an epoxy-based resin. As described above, when the resin layer 9 is used in place of a conventional insulating tape to fix the lead 1, a moisture content in the fixed portion decreases. For this reason, steam generated by heat in practical use can be suppressed, and probability of forming cracks in the sealing resin layer 2 can be reduced. When the filler content is smaller than that in the sealing resin layer 2, probability of clogging filler between the lead 1 and the circuit surface 3a can be reduced. When the diameter of filler itself is reduced, the filler can be prevented from being clogged. Therefore, stress based on the difference between the coefficient of contraction of the resin and the coefficient of contraction of the filler in solidification of a sealing resin can be prevented from being generated, so that the semiconductor chip 3 can be prevented from being cracked. A method of manufacturing a resin-sealed semiconductor device according to the embodiment will be described below. This manufacturing method comprises: the first step of coating the lead fixing resin layer 9 on the circuit surface 3a of the semiconductor chip 3; the second step of fixing the distal ends of the plurality of leads 1 to the semiconductor chip 3 with the lead fixing resin layer 9; the third step of bonding the distal ends of the leads 1 and the electrodes 10 formed on the circuit surface 3a to each other; and the fourth step of sealing the semiconductor chip 3 and the leads 1 with the sealing resin layer 2. The respective steps will be sequentially described below. In the first step, as shown in FIG. 3(A) serving as a side view and FIG. 3(B) serving as a plan view, a resin 9a for forming the lead fixing resin layer 9 is liquefied, and the liquid resin 9a is supplied from a dispenser 11 onto the circuit surface 3a. The resin 9a is coated on a position where the leads 1 are fixed, i.e., both the sides of electrode rows in the arrangement direction of the electrodes 10. The coated liquid resin 9a initially formes hemisphere shape in the first step. In the second step, as shown in FIG. 4(A) serving as a side view, the semiconductor chip 3 is set in a recessed portion 12a formed in a heat block 12, and the plurality of leads 1 are pressed against the liquid resin 9a from the upper side of FIG. 4(A) to spread the liquid resin 9a. The heat block 12 is kept at a temperature of 80°C to 100°C, and the lead fixing resin layer 9 serving as a thermosetting resin is solidified for about one minute. The depth of the recessed portion 12a is set such that the level of the circuit surface 3a is lower than a periphery surrounding surface of the recessed portion 12a by 40 to 100 µm. The lead 1 is arranged to extend from both the sides of the semiconductor chip 3 to the central electrode 10 as shown in FIG. 4(B) serving as a plan view, and the lead 1 is fixed to the semiconductor chip 3 with the lead fixing resin layer 9. In the third step, the electrode 10 of the semiconductor chip 3 is electrically connected to the distal end of the lead 1 fixed to the semiconductor chip 3 in the second step by bonding with the wire 5. And in the fourth step, the semiconductor chip 3, the distal end of the lead 1, and the wire 5 are sealed with the sealing resin layer 2, and the sealing resin layer 2 is solidified. Thereafter, lead processes such as diver cutting, lead cutting, and lead bending are performed to complete the semiconductor device shown in FIG. 1. As described above, according to the present invention, when a lead fixing resin layer is used to fix a lead before bonding to a semiconductor chip, a moisture content in the fixed portion decreases. For this reason, steam generated by heat in practical use can be suppressed, and probability of forming cracks in the sealing resin layer can be reduced. In addition, when the diameter of filler contained in the lead fixing resin layer is reduced, probability of clogging the filler between the lead and the semiconductor chip can be reduced. When the diameter of filler itself is reduced, the filler can be prevented from being clogged, and the semiconductor can be prevented from being cracked in solidification of the sealing resin. Furthermore, when the filler content in the lead fixing resin layer is made smaller than that in the sealing resin layer, probability of clogging filler between the lead and the circuit surface can be reduced. In this manner, stress based on the difference between the coefficient of contraction of the resin and the coefficient of contraction of the filler in solidification of the sealing resin can be prevented from being generated, so that the semiconductor chip can be prevented from being cracked.

Claims: A resin-sealed semiconductor device comprising: a semiconductor chip (3) having a circuit surface on which a plurality of electrodes (10) are formed; a plurality of leads (1) which are arranged at predetermined gaps with respect to said semiconductor chip (3) in such a manner that distal ends of said leads (1) overlap said semiconductor chip (3), and which are electrically connected to said respective electrodes (10); a lead fixing resin layer (9) filled between said semiconductor chip (3) and said leads (1) to fix said leads (1) to said semiconductor chip (3); and a sealing resin layer (2) which is coated to cover the distal ends of said leads (1) and said semiconductor chip (3) which are fixed with said lead fixing resin, wherein both said lead fixing resin layer (9) and said sealing resin layer (2) contain filler, characterized in that the ratio by weight of the filler contained in said lead fixing resin layer (9) is lower than the ratio by weight of the filler contained in said sealing resin layer (2), and the diameter of the filler contained in said lead fixing resin layer (9) is 1/10 to 1/5 the diameter of the filler contained in said sealing resin layer (2). A resin-sealed semiconductor device according to claim 1 wherein the diameter of the filler contained in said lead fixing resin (9) layer is 10 µm. A resin-sealed semiconductor device according to claim 1, wherein the filler contained in the sealing resin layer (2) has a diameter of 50 to 100 µm at a ratio by weight of about 80% and the remaining 20% is an epoxy-based resin. A resin-sealed semiconductor device according to claim 1, wherein the diameter of the filler contained in said lead fixing resin layer (9) is 1/10 the gap between said leads (1) and said semiconductor chip (3) at an overlapping portion therebetween. A method of manufacturing a resin-sealed semiconductor device, which is formed by sealing a semiconductor chip (3) and leads (1) with a sealing resin layer (2) containing filler, comprising: the step of coating a lead fixing resin layer (9), which contains filler, on a circuit surface of said semiconductor chip (3); the step of fixing the distal ends of a plurality of leads(1) to said semiconductor chip (3) with said lead fixing resin layer (9); the step of bonding the distal ends of said leads (1) and electrodes (10) formed on said circuit surface; and the step of sealing said semiconductor chip (3) and said leads (1) with said sealing resin layer (2), characterized in that the ratio by weight of the filler contained in said lead fixing resin layer (9) is lower than the ratio by weight of the filler contained in said sealing resin layer (2), and the diameter of the filler contained in said lead fixing resin layer (9) is 1/10 to 1/5 the diameter of the filler contained in said sealing resin layer (2). A method of manufacturing a resin-sealed semiconductor device according to claim 5, wherein the diameter of the filler contained in said lead fixing resin layer (9) is 1/10 the gap between said leads (1) and said semiconductor chip (3) at an overlapping portion therebetween.

Inventors: ANZAI NORITAKA, OHUCHI SHINJI, ANZAI, NORITAKA, OHUCHI, SHINJI
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1998
Main classification: H01L23
IPC codes: H01L23