Method and device for making a metal bump with an increased height

Abstract

A device for making metal bumps includes a hard conical tubular member having a vertical passage which is conical in shape and has a larger diameter at a bottom such that a lower portion of the vertical passage is larger than an upper portion of the vertical passage, whereby a metal wire is inserted into the vertical passage of the hard conical tubular member, with a lower end of the metal wire protruded downwardly out of the vertical passage, the lower end of the metal wire is melted to form a ball, the hard conical tubular member is approached to a raised platform formed on a top of a chip, and a load is applied to the metal wire and the metal wire is heated and bonded on the pad of die and ultrasonic energy is applied to deform the melted metal so as to fill up the lower portion of the vertical passage thereby forming a metal bump on the raised platform of the chip, and finally the hard conical tubular member is removed to pull off the necking position between the metal wire and a top of the metal bump thereby leaving the metal bump on the raised platform of the chip.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention is related to a method and device for making a metal bump with an increased height and in particular to one which can increase the connection reliability between the metal bump and the chip and enlarging the contact area between the metal bump and the metal or solder ball.

[0003] 2. Description of the Prior Art

[0004] Various kinds of methods of making metal bumps on a chip have been developed for flip chip on board (FCOB) technology with a small number of input pins or a small number of Input/Output pins or for flip chip in package (FCIP) with a large number of Input/Output pins, such as evaporation plating, splash plating, electroplating, printing, spraying, and bonding. However, the capillary tube is still the most commonly used tool for making metal bumps by means of wire bonding. The capillary tube has an inner diameter with an inner wall and has a larger diameter at the upper end than the lower end. A metal wire is inserted into the capillary tube and the lower end of the metal wire is melted to form a ball shaped member by electric spark. Then, ultrasonic vibration and pressure deformation processing are applied to the capillary tube to join the inter-metallic compounds between the wire and the chip. When the capillary tube is removed, a metal bump will be formed on the raised platform of the chip. Thereafter, a metal or solder ball is soldered on the metal bump.

[0005] However, due to the limitation of the design of the capillary tube, the metal bump will have a spherical surface which is insufficient to provide a large contact area and a reliable structure for joining other component parts. Furthermore, the bottom of the metal bump will tend to go beyond the lower opening of the capillary tube under pressure thereby making it difficult to control. Moreover, as the metal bump has a spherical surface, there will not be sufficient area in contact with a metal or solder ball. In addition, the metal bump is so short that the metal or solder ball must be soldered to the metal bump at a very low position thereby making it difficult to make the connection between the chip and the fingers of a substrate (or lead frame, chips, metal bumps or the like) and therefore influencing the qualification rate of products.

[0006] Therefore, it is an object of the present invention to provide a method and device for making a metal bump with an increased height which can obviate and mitigate the above-mentioned drawbacks.

SUMMARY OF THE INVENTION

[0007] This invention is related to a method and device for making a metal bump with an increased height.

[0008] It is the primary object of the present invention to provide a method and device for making metal bumps with an increased height which can increase the joining strength with other metal bumps or pads of a die.

[0009] It is another object of the present invention to provide a method and device for making metal bumps with an increased height which can enlarge the contact area with the metal or solder ball.

[0010] It is still another object of the present invention to provide a method and device for making metal bumps with an increased height which can increase its reliability in joining with other component parts.

[0011] It is a further object of the present invention to provide a method and device for making metal bumps which have an increased height but are small in diameter.

[0012] The foregoing object and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts.

[0013] Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a sectional view of a capillary tube according to the present invention;

[0015] FIG. 2A illustrates the lower end of a metal wire being melted to form a ball shaped member according to the present invention;

[0016] FIG. 2B illustrates how the lower end of the metal wire is joined with the chip according to the present invention;

[0017] FIG. 2C illustrates a metal bump according to the present invention;

[0018] FIGS. 3A and 3B illustrate the connection between the metal bump and the metal or solder ball according to the present invention; and

[0019] FIGS. 4A and 4B illustrate the connection between the metal bump and the metal or solder ball according to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings. Specific language will be used to describe same. It will, nevertheless, be understood that no limitation of the scope of the invention is thereby intended, alterations and filter modifications in the illustrated device, and further applications of the principles of the invention as illustrated herein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0021] Referring to the drawings and in particular to FIG. 1 thereof, the metal bump according to the present invention is manufactured by a hard conical tubular member 20 having a vertical passage 21 which is conical in shape and has a larger diameter at the bottom 231 so that the lower portion 23 of the vertical passage 21 is larger than the upper portion 24 of the vertical passage 21. The vertical passage 21 has an inner surface 22.

[0022] Referring to FIGS. 2A, 2B and 2C, a metal wire 3 is inserted into the vertical passage 21 of the hard conical tubular member 20, with its lower end protruded downwardly out of the vertical passage 21. Then, the lower end of the metal wire 3 is melted to form a ball 31. Thereafter, the hard conical tubular member 2 is approached to a raised platform 11 formed on the top of a chip 1, and a load (not shown) is applied to the metal wire 3 and the metal wire 3 is heated and bonded on the pad of die and ultrasonic energy is applied to deform the melted metal so as to fill up the lower portion 23 of the vertical passage 21, thereby forming a metal bump 32 on the raised platform 11 of the chip 1. Thereafter, the hard conical tubular member 2 is removed to pull off the necking position between the metal wire 3 and the top of the metal bump 32 thereby leaving the metal bump 32 on the raised platform 11 of the chip 1. As the bottom opening of the lower portion 23 of the vertical passage 21 is formed with an angle 231, the metal bump 32 will be formed with a flange 321 at the bottom thereof (see FIG. 2B).

[0023] Accordingly, the metal bump 32 will have an increased height 232 thereby increasing the joining capability between the metal bump 32 and the raised platform 11 of the semiconductor chip 1 and enlarging the contact area 33 between the metal bump 32 and the metal or solder ball 4.

[0024] As the metal or solder ball 4 is joined to the metal bump 32 (see FIGS. 3A and 3B), the metal or solder ball 4 will be pressed by a soldering finger 5 thereby deforming the shape of the metal or solder ball 4 and therefore causing the deformed metal or solder ball 4 to go outwardly. In the meantime, the flange 321 of the metal bump 32 will block the metal or solder ball 4 to overflow to the raised platform 11 of the chip 1. Referring to FIGS. 4A and 4B, according to the prior art, the metal or solder ball 4′ will be pressed by a soldering finger 5′ when the metal or solder ball 4′ is joined to the metal bump 32′, thereby deforming the shape of the metal or solder ball 4′ and therefore causing the deformed metal or solder ball 4′ to overflow to the raised platform 11′ of the chip 1′. Hence, the connection reliability between the chip and the fingers of a substrate (or lead frame, chips, metal bumps or the like) will be decreased and therefore influencing the qualification rate of products.

[0025] It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above.

[0026] While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention.

Claims

1. A device for making metal bumps comprising a hard conical tubular member having a vertical passage which is conical in shape and has a larger diameter at a bottom such that a lower portion of said vertical passage is larger than an upper portion of said vertical passage, whereby a metal wire is inserted into said vertical passage of said hard conical tubular member, with a lower end of said metal wire protruded downwardly out of said vertical passage, said lower end of said metal wire is melted to form a ball, said hard conical tubular member is approached to a raised platform formed on a top of a chip, and a load is applied to said metal wire and said metal wire is heated and bonded on the pad of die and ultrasonic energy is applied to deform said melted metal so as to fill up said lower portion of said vertical passage thereby forming a metal bump on said raised platform of said chip, and finally said hard conical tubular member is removed to pull off the necking position between said metal wire and a top of said metal bump thereby leaving said metal bump on said raised platform of said chip.