Bonding apparatus

Abstract: A depression jig, having a depression chip and a holder for holding the depression chip, is provided which depresses against a wiring substrate a semiconductor chip placed on the wiring substrate. The holder has portions defining penetrations vertically running through the holder. Optical fibers are inserted into the penetrations. A light ray radiates from the optical fiber. The light ray is incident upon the top surface of the depression chip, enters the depression chip, is reflected from a side surface of the depression chip onto the undersurface of the depression chip, and is emitted from the undersurface of the depression chip as an outgoing light ray. A photo-curing resin supplied between the semiconductor chip and the wiring substrate is irradiated with such an outgoing light ray, so that the photo-curing resin hardens.

Description: BONDING APPARATUS This invention generally relates to bonding apparatus for mounting semiconductor chips with many, low-pitch projecting electrodes (i.e., bumps) onto a wiring substrate at high density. More specifically, it pertains to a bonding apparatus for bonding such semiconductor chips onto an opaque wiring substrate formed of such materials as silicon or ceramic by means of what is known in the semiconductor industry as "facedown bonding". In the art, there is a bonding method known as the MBB (micro bump bonding) method in which a semiconductor chip having on its undersurface many, low-pitch bumps is mounted onto a wiring substrate having on its top surface wires so that a batch wireless bonding can be accomplished by means of the facedown bonding. FIGURE 5 illustrates a bonding apparatus of the MBB method. This bonding apparatus includes a mounting stand 2, a depression jig 4, a pressurizer 5, and several optical fibers 6. Placed onto the mounting stand 2 is a wiring substrate 1 of such materials as silicon or ceramic, the wiring substrate 1 having wires on its top surface. The depression jig 4 is used to depress against the wiring substrate 1 a semiconductor chip 3 with bumps 3a on its undersurface, the semiconductor chip 3 being set in place on the wiring substrate 1 that is placed on the mounting stand 2. The pressurizer 5 is disposed above the depression jig 4 and is used to push down the depression jig 4. The optical fibers 6, disposed alongside the depression jig 4, send out respective light rays upon a photo-curing resin (i.e., the resin which hardens on application of light) supplied between the wiring substrate 1 and the semiconductor chip 3. The mounting stand 2 is mobile, which facilitates the alignment of the semiconductor chip 3 with the wiring substrate 1, in bonding these two elements together. The depression jig 4 has a holder 7 and a depression chip 8. The depression chip 8 is made of hard metal, ceramic, or the like materials, and is jointed to the undersurface of the holder 7. The top surface of the holder 7, indicated by the reference numeral 7a, is jointed to the pressurizer 5. FIGURE 6 shows how such a bonding apparatus mounts the semiconductor chip 3 onto the wiring substrate 1. As shown in FIGURE 6a, the wiring substrate 1, with its top surface up, is placed onto the mounting stand 2. Then, the top surface of the wiring substrate 1 is coated with a photo-curing resin 9 having the property of insulation. The wire 1a is of such materials as Cr, Au, Al, Cu, or the like materials. The bump 3a, on the other hand, is of such materials as Au, Al, Cu, or the like materials. For the photo-curing resin 9, such materials as ultra violet ray-curing epoxy resin, silicon resin, acrylic resin, or the like materials may be employed. As shown in FIGURE 6b, the semiconductor chip 3 is set in place on the wiring substrate 1, with the bump 3a of the semiconductor chip 3 aligned with the wire 1a of the wiring substrate 1 as well as with the photo-curing resin 9 intervened between the semiconductor chip 3 and the wiring substrate 1. As shown in FIGURE 6c, the descent movement of the pressurizer 5 causes the depression jig 4 to press the semiconductor chip 3 downward, whereby the semiconductor chip 3 is pressed against the wiring substrate 1. The photo-curing resin 9 lying between the bump 3a and the wire 1a is therefore extruded from between the bump 3a and the wire 1a. As a result, the bump 3a is brought into electrical contact with the wire 1a. Thereafter, the optical fibers 6 simultaneously send out respective ultra violet rays upon the photo-curing resin 9, with the semiconductor chip 3 pressed onto the wiring substrate 1, whereby the photo-curing resin 9 hardens on application of the ultra violet rays. In other words, while making reflection and scattering between the undersurface of the semiconductor chip 3 and the top surface of the wiring substrate 1, the ultra violet rays enter the photo-curing resin 9 to harden it. The several optical fibers 6 are provided around the depression jig 4, the reason for which is that the photo-curing resist 9 around the semiconductor chip 3 cannot simultaneously be hardened by only one optical fiber. If the optical fiber 9 is to be disposed outside every side of the semiconductor chip 3, this requires four optical fibers. If the optical fiber 9 is to be disposed outside every side and corner of the semiconductor chip 3, this requires eight optical fibers. As shown in FIGURE 6d, the pressurizer 5 has moved away from over the semiconductor chip 3. The semiconductor chip 3 is now firmly fixed to the wiring substrate 1, and the bump 3a of the semiconductor chip 3 is brought into electrical contact with the wire 1a of the wiring substrate 1 due to shrinkage force of the photo-curing resin 9. As shown in FIGURE 7a, if there is a great space (i.e., the width W1) between a semiconductor chip 3A being depressed with the depression jig 4 and its neighboring semiconductor chip 3B, the optical fiber 6 is able to send out ultra violet rays through such a great space upon the photo-curing resin 9. A tilt angle, , formed between an ultra violet ray emitted from the optical fiber 6 and one side face of the semiconductor chip 3A, is determined based on the efficiency of the hardening of the photo-curing resin 9 (FIGURE 7a). As shown in FIGURE 7b, if the semiconductor chip 3A and the neighboring semiconductor chip 3B are mounted in close proximity, that is, if there is a close space (the width W2) between these two semiconductor chips, some ultra violet rays, given off from the optical fiber 6, are interfered due to the presence of the neighboring semiconductor chip 3B. This presents a problem that the efficiency of the irradiation relative to the photo-curing resin 9 lying around the semiconductor chip 3A decreases. As shown in FIGURE 7c, a depression surface 8a (i.e., the undersurface of the depression chip 8) is generally given a slightly greater area compared to the semiconductor chip 3 so that even though the relative positions of the depression jig 4 and the semiconductor chip 3 deviate, the depression surface 8a of the depression chip 8 can manage to equally depress the semiconductor 3. This, however, presents another problem that some ultra violet rays, given from the optical fiber 6, are interfered by the depression surface 8a whose area is greater than that of the semiconductor chip 3. This results in the decrease of the efficiency of the irradiation relative to the photo-curing resin 9. The present invention was made to solve the foregoing problems. In accordance with the invention, the depression chip is formed of a light ray transmission material through which light rays can pass. Outgoing light rays, given off from the optical fiber, are so directed that they are incident upon the top surface of the depression chip thereby entering the depression chip and being reflected from the side surfaces of the depression chip. Then such light rays are sent out from the undersurface of the depression chip upon the photo-curing resin. The invention discloses a bonding apparatus comprising the features of claim 1. As described above, in accordance with the invention, a light ray for hardening the photo-curing resin strikes the incident surface of the depression chip, and enters inside, is reflected from the reflective surface onto the depression surface, and is emitted out of the depression surface. As a result, the light ray is diagonally sent out upon the photo-curing resin. With this arrangement, even though there is a close space between one semiconductor chip and its neighboring semiconductor chip, that is, they are mounted at a high density, the light rays positively reach the photo-curing resin. This prevents the efficiency of the irradiation relative to the photo-curing resin from decreasing. Additionally, since the light rays for hardening the photo-curing resin are emitted from the depression surface of the depression chip of a light ray transmission material, the light rays can make their way to the photo-curing resin without any obstacles, while on the other hand, the light rays are interfered in the prior art technique due to the conventional depression chip which is made of a non-light ray transmission material. Thus, the efficiency of the irradiation relative to the photo-curing resin will not decrease in the present invention. The depression surface of the depression chip is greater than the semiconductor chip without suffering from ill effects, since the depression chip no longer blocks the course of the light rays. This allows the depression surface of the depression chip to positively depress the semiconductor chip even though the relative positions of the depression chip and the semiconductor chip deviate. Further, if an angle, formed between the depression surface and each reflective surface of the depression chip, is made obtuse, this causes a light ray, given off from the light feed means, to fall upon the incident surface of the depression chip at a right angle. This results in simplifying the arrangement of the light feed means. A light ray, which is incident upon the incident surface of the depression chip, enters the depression chip and is fully reflected from the reflective surface onto the depression surface, if the incident surface and the depression surface of the depression chip are in a parallel relationship with each other, and if the relation of sin α > n 2 /n 1 holds where α is the angle formed between the depression surface and the reflective surfaces of the depression chip, n 1 is the index of refraction of light relative to the light ray transmission material making up the depression chip, and n 2 is the index of refraction of light relative to a layer outside the depression chip. This improves the efficiency of the irradiation relative to the photo-curing resin. Each light ray, which is incident upon the incident surface of the depression chip, enters inside and is reflected from the reflective surface, reaches the depression surface, if one side of the depression surface of the depression chip is longer than one side of the semiconductor chip by a given length, if the other sides of the depression surface are longer than the other sides of the semiconductor chip by the aforesaid given value, respectively, and if the relation of L ≧ 2t/tan β holds (L: the given value; t: the thickness of the semiconductor chip; and β: the angle formed between the depression surface and an outgoing light ray emitted from the depression surface). This also improves the efficiency of the irradiation relative to the photo-curing resin. It is preferable that the light feed means sends out ultra violet rays, that the light ray transmission material is an ultra violet ray transmission material such as quartz glass. If the light feed means comprises optical fibers, it facilitates the feed of light rays. The holder is provided with portions defining four penetrations in a square formation. The corresponding optical fibers are inserted into the penetrations and send out respective light rays that produce uniform hardening of the photo-curing resin lying between the semiconductor chip and the wiring substrate. If the optical fiber is mobile horizontally, this facilitates the correction of the light ray emitting position of the optical fiber when an error occurs. If the optical fiber is mobile vertically, the incident efficiency of the light rays, given off from the optical fiber, to the incident surface of the depression chip can be adjusted. FIGURE 1 shows in cross section the organization of a bonding apparatus of an embodiment of the present invention. FIGURE 2 is a cross sectional view illustrating geometrical dimensions of a depression surface of the bonding apparatus of the invention. FIGURE 3 shows in cross section how the bonding apparatus of the invention mounts a semiconductor chip onto a wiring substrate. FIGURE 4 shows the arrangement relation of a depression surface of a depression chip versus a semiconductor chip. FIGURE 5 shows in cross section the organization of a prior art bonding apparatus. FIGURE 6 shows in cross section how the prior art bonding apparatus mounts a semiconductor chip onto a wiring substrate. FIGURE 7 shows in cross section how the prior art bonding apparatus causes problems in mounting a semiconductor chip onto a wiring substrate. A preferred embodiment of the invention is now described by reference to the accompanying drawings. A bonding apparatus in accordance with the invention, shown in FIGURE 1, comprises a mounting stand 2, a depression jig 4, and a pressurizer 5. Placed onto the mounting stand 2 is a wiring substrate 1 of such materials as silicon or ceramic. The wiring substrate 1 has on its top surface wires. The depression jig 4 is used to depress against the wiring substrate 1 a semiconductor chip 3 with bumps 3a on its undersurface, the semiconductor chip 3 being set in place on the wiring substrate 1 that is placed on the mounting stand 2. The pressurizer 5 is disposed above the depression jig 4 and pushes down the depression jig 4. The mounting stand 2 has a flat placement surface 2a onto which the wiring substrate 1 is placed, and is mobile horizontally thereby making it possible to align the wiring substrate 1, placed on the placement surface 2a, with the semiconductor chip 3, in bonding these two element together. The depression jig 4 comprises a holder 7, fixed to the undersurface of the pressurizer 5 and having a rectangular undersurface, and a depression chip 8 of a light ray transmission material, fixed to the undersurface of the holder 7 with adhesives. Provided in the holder 7 are portions defining four penetrations 10 in a square formation. Each one of the four penetrations 10 vertically runs through the holder 7, and corresponding four optical fibers 6, serving as light feed means for sending out ultra violet rays, are inserted from upward to downward into these four penetrations 10. The depression chip 8, of such ultra violet ray transmission materials as quartz glass, is of a frustum of a pyramid. The depression chip 8 has an incident surface 8b that is a flat rectangular top surface upon which light rays sent out from the optical fibers 6 are incident, a depression surface 8a that is a flat rectangular undersurface parallel with the incident surface 8b, and reflective surfaces 8c that are flat side surfaces so that light rays that are incident upon the incident surface 8b and enter inside are reflected from the reflective surfaces onto the depression surface 8a. The sides of the depression surface 8a are longer than the corresponding sides of the semiconductor chip 3. To sum up, the outgoing light rays, given off from the optical fibers 6, are incident upon the incident surface 8b of the depression chip 8 thereby entering inside. Then, the light rays are reflected from the respective reflective surfaces 8c onto the depression surface 8a, and are emitted from the depression surface 8a so that the side faces of the semiconductor chip 3 are irradiated with the light rays. The provision of the four penetrations 10 in the holder 7 arranged in a square formation makes it possible for the side faces of the semiconductor chip 3 to be irradiated with the light rays at the same time. An angle, α, formed between the depression surface 8a and each reflective surface 8c of the depression chip 8, is obtuse, and the relation of sin α > n 2 /n 1 holds where n 1 is the index of refraction of light relative to the light ray transmission material making up the depression chip 8, and n 2 is the index of refraction of light relative to a layer outside the depression chip 8. A light ray, which falls upon the incident surface 8b of the depression chip 8 at Point A and enters inside, is reflected from the reflective surface 8c at Point B onto the depression surface 8c without penetrating through the reflective surface 8c. This allows each light ray that is incident upon the incident surface 8b of the depression chip 8 and enters inside to be fully reflected from the reflective surface 8c, which leads to the efficiency of the irradiation relative to the photo-curing resin being good. If the depression chip 8 is of a quartz glass, n 1 = 1.5, and if the layer outside the depression chip 8 is air, n 2 = 1.0. Thus, the angle, α should be set within the range of from 138.3° down to 90° . As shown in FIGURE 2a, one side of the depression surface 8a of the depression chip 8 is longer than one corresponding side of the semiconductor chip 3 by a given length L, and the other sides of the depression surface 8a are longer than the other corresponding sides of the semiconductor chip 3 by the given length L, respectively. With this arrangement, light rays are reflected from the reflective surfaces 8c onto the depression surface 8a and are emitted from the depression surface 8a outside the semiconductor chip 3, with no light rays reflected from the top surface of the semiconductor chip 3. If, as shown in FIGURE 2a, the size of the depression surface 8a of the depression chip 8 corresponds to that of the semiconductor chip 3, the light rays, reflected from the reflective surfaces 8c of the depression chip 8, are reflected from the top surface of the semiconductor chip 3. Thus, the light rays are not emitted from the depression surface 8a. Reference is now made to FIGURE 3 to illustrate how the bonding apparatus of the invention mounts the semiconductor chip 3 onto the wiring substrate 1. As shown in FIGURE 3a, the wiring substrate 1 of such materials as silicon or ceramic having on its top surface wires 1a is placed onto the placement surface 2a of the mounting stand 2. The wire 1a is of Au, Cu, Al, or the like materials, and has a thickness of approximately 0.1 µ to 35 µm. Thereafter, the top surface of the wiring substrate 1 is coated with a photo-curing resin 9. The photo-curing resin 9 may be formed of epoxy resin, silicon resin, acrylic resin, or the like materials with the degree of viscosity ranging from 1000cp to 5000cp. As shown in FIGURE 3b, the bump 3a of the semiconductor chip 3 is aligned with the wire 1a of the wiring substrate 1, before placing the semiconductor chip 3 onto the wiring substrate 1. As shown in FIGURE 3c, the semiconductor chip 3 is depressed with the depression surface 8a of the depression chip 3 so that the semiconductor chip 3 is pressed onto the wiring substrate 1. As a result of this, the photo-curing resin 9 lying between the bump 3a and the wire 1a is extruded from between the bump 3a and the wire 1a. Thus, the bump 3a is brought into electrical contact with the wire 1a. Depression force applied by the depression chip 8 to the semiconductor chip 3 to depress it is 10g to 50g per bump. Then, with the semiconductor chip 3 pressed against the wiring substrate 1, the optical fibers 6 send out respective ultra violet rays upon the photo-curing resin 9. The following will describe how an ultra violet ray, given off from the optical fiber 6, reaches the photo-curing resin 9 to harden it. An outgoing ultra violet ray, given off from the optical fiber 6, is incident upon the incident surface 8b of the depression chip 8 at Point A at a right angle to the incident surface 8b, travels in the depression chip 8, and is fully reflected from the reflective surface 8c at Point B. Thereafter, the ultra violet ray is emitted from the depression surface 8a at Point C at an outgoing angle of β to the depression surface 8a. Between the angle α, formed between the depression surface 8a and the reflective surface 8c of the depression chip 8 and the outgoing angle β, there is a relationship by the Snell laws of refraction: sin(90° - β) = (n 1 /n 2 × sin(2 α - 180° ) where n 1 is the index of refraction of light relative to the light ray transmission material making up the depression chip 8, and n 2 is the index of refraction of light relative to the layer outside the depression chip 8. The ultra violet ray, thus emitted from the depression surface 8a, falls on the photo-curing resin 9 lying between the semiconductor chip 3 and the wiring substrate 1 thereby hardening the photo-curing resin 9. The four optical fibers 6, inserted into the four penetrations 10 in the holder 7, simultaneously send out respective ultra violet rays so that such ultra violet rays are simultaneously emitted from the depression surface 8a. As a result, the photo-curing resin 9 lying alongside the side faces of the semiconductor chip 3 is simultaneously hardened. As shown in FIGURE 3d, the depression chip 8 is moved away from over the semiconductor chip 3. The semiconductor chip 3 is now firmly fixed to the wiring substrate 1, and the bump 3a of the semiconductor chip 3 establishes electrical contact with the wire 1a of the wiring substrate 1 due to shrinkage force of the photo-curing resin 9. The relation between the size of the depression surface 8a of the depression chip 8 and the size of the semiconductor chip 3 is now described below. As shown in FIGURE 3c, when an ultra violet ray, emitted from the depression surface 8a at Point C, is incident upon the photo-curing resin 9 at Point D, the relation of tan β = ED/CE holds where E is the end of the top surface of the semiconductor chip 3. In other words, if the difference between the length of one side of the depression surface 8a and the length of one corresponding side of the semiconductor chip 3 is L, if the differences between the lengths of the other sides of the depression surface 8a and the lengths of the other corresponding sides of the semiconductor chip 3 are likewise L, respectively, and if the thickness of the semiconductor chip 3 is t, the relation among L, t, and β is required to be such that L ≧ 2t/tan β. In depressing the semiconductor chip 3 with the depression chip 8, as shown in FIGURE 4a, the relative positions of the depression chip 8 and the semiconductor chip 3 are generally so arranged that the sides of the former run parallel with the corresponding sides of the latter, respectively. However, a different arrangement variation from the above may be employed wherein each side of the depression surface 8a is arranged at an angle of 45° to each side of the semiconductor chip 3, as shown in FIGURE 4b. With this arrangement, the hardening time for hardening the photo-curing resin 9 is reduced to a half, since the photo-curing resin 9 lying alongside the side faces of the semiconductor 9 is irradiated with light rays from two directions.

Claims: A bonding apparatus comprising: a mounting stand (2) onto which a wiring substrate (1) with wires on its top surface is placed; a depression jig (4) for depressing against the wiring substrate (1) a semiconductor chip (3) with bump electrodes (3a) on its undersurface, the semiconductor chip being set in place on the wiring substrate (1) that is placed on the mounting stand; pressure means (5) for pressurizing the depression jig (4) downward; and light feed means (6) for sending out a light ray upon a photo-curing resin having the property of insulation, the photo-curing resin being supplied between the wiring substrate (1) and the semiconductor chip (3); wherein: the depression jig (4) has a depression chip of a light ray transmissive material and a holder (7) for holding the depression chip; the holder (7) has a portion defining a penetration (10) through which the light ray fed by the light feed means (6) vertically passes; the top surface of the depression chip is a flat incident surface (8b) upon which the light ray which has passed through the penetration (10) is incident; the undersurface of the depression chip is a flat depression surface (8a) having a size larger than that of the semiconductor chip (3) for depressing the semiconductor chip (3) against the wiring substrate (1); and the side surfaces (8c) of the depression chip (8) are reflective surfaces so that the light ray which was incident upon the incident surface (8b) and has entered the depression chip is reflected from one of the reflective surfaces (8c) onto the depression surface; and the light feed means (6) hardening the photo-curing resin by sending out the light ray which falls upon the incident surface (8b) of the depression chip (8), enters the depression chip, is emitted out of the depression surface (8a), and reaches the photo-curing resin. The bonding apparatus of claim 1, wherein an angle (α) formed between the depression surface (8a) and the reflective surfaces (8c) of the depression chip (8) is an obtuse angle. The bonding apparatus of claim 2, wherein the incident surface (8b) and the depression surface (8a) of the depression chip (8) are parallel with each other, and the relationship among the angle (α) formed between the depression surface (8a) and the reflective surfaces (8c) of the depression chip, the index (n 1 ) of refraction of light relative to the light ray transmissive material making up the depression chip (8), and the index (n 2 ) of refraction of light relative to a layer outside the depression chip (8) satisfies the relation sin α > n 2 /n 1 . The bonding apparatus of one of claims 1 to 3, wherein one side of the depression surface (8a) of the depression chip (8) is greater than one corresponding side of the semiconductor chip (3) by a given length (L/2) the other sides of the depression surface (8a) are greater than the other corresponding sides of the semi-conductor chip (3) by the given length (L/2) respectively, and the relationship among the given length (L/2) the thickness (t) of the semiconductor chip, and the angle (β) formed between the depression surface (8a) and an outgoing light ray emitted from the depression surface satisfies the relation L ≥ 2t/tan β. The bonding apparatus of one of claims 1 to 4, wherein the light feed means (6) sends out ultra violet rays, and the light ray transmissive material is an ultra violet ray transmissive material. The bonding apparatus of claim 5, wherein the light ray transmissive material is a quartz glass. The bonding apparatus of one of claims 1 to 6, wherein the light feed means is an optical fiber (6). The bonding apparatus of one of claims 1 to 7, wherein there are provided portions defining four penetrations (10) in the holder (7) in a square formation, and the optical fibers (6) are inserted into the respective penetrations (10). The bond apparatus of claim 7, wherein the optical fiber (6) is so arranged that it can move horizontally. The bonding apparatus of claim 7, wherein the optical fiber (6) is so arranged that it can move vertically.

Inventors: FUJIMOTO HIROAKI, HATADA KENZO, TAKESHITA YOSHINOBU, TAMAKI TOMOHIRO, FUJIMOTO, HIROAKI, HATADA, KENZO, TAKESHITA, YOSHINOBU, TAMAKI, TOMOHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRONICS CORP, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., MATSUSHITA ELECTRONICS CORPORATION
Application year: 1992
Main classification: H01L21
IPC codes: H01L21, H05K13, H05K3