Bond tool for notching a lead in semiconductor package

Abstract

A bond tool is used in semiconductor package to break a lead at a notch formed thereon and then bonds the broken lead to a die pad. In an embossing-type bond tool, an end thereof is provided with a projected portion for vertically pressing against the lead to form a transversely extended groove thereon. In a scissor-type bond tool, an end thereof is formed into two opposite sharp blades for horizontally cutting the lead at two lateral edges thereof to provide two symmetrical cuts. Unlike the conventional notches that are formed on the lead during the complicate forming process of the lead, the groove and the symmetrical cuts are easily formed on the straight lead without notch to provide a weak point at reduced manufacturing cost. The difficulties in forming the conventional notches on the lead due to the highly precise lead windows, lead width, and lead pitch can therefore be avoided and thus improve the yield for manufacturing of lead bond substrates.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a bond tool for notching a lead in semiconductor package, and more particularly to a bond tool either having a projection or two opposite sharp blades like a pair of scissors provided at an end thereof for stamping a vertical groove on a lead or forming two symmetrical cuts on two lateral edges of a lead, respectively, so that the bond tool is suitable for use in the increasingly precise lead bonding in semiconductor package to overcome difficulties in forming notches on the leads in conventional manners.

[0002] It has been almost 40 years since the integrated circuit (IC) was developed, and various kinds of electronic products employing IC techniques have become prerequisite items in people's daily life. With the quick development in IC techniques, IC packaging technique has also been rapidly developed and constantly improved. Since the industrial field and the overall market demand for electronic products as compact as possible, it has become most manufacturers' target to develop various kinds of IC products having high operating speed, high number of input/output (I/O) pins, and minimized dimensions. To meet these requirements, IC has been designed to have constantly increased integration. The feature dimension of an IC has been reduced from 0.6 &mgr;m at the early stage to currently available 0.13 &mgr;m, and the number of I/O pins has been constantly increased to a range from 300 to 600 pins or even higher. The requirements for even finely structured IC elements with high performance challenge the electronic industries. Alight, thin, short, and small IC package has become a must in the future.

[0003] In a variety of conventional semiconductor packages, there is one type being referred to as a chip scale package (CSP). The CSP includes a so-called PBGA package structure that can be further divided into two types. Please refer to FIGS. 2 and 3 that show the first and the second type, respectively, of the PBGA package structure for the CSP. The first type of PBGA package structure shown in FIG. 2 has leads 2 located at two lateral sides of the package and is referred to as an edge bond package. On the other hand, the second type of &mgr;BGA package structure shown in FIG. 3 has leads 2 located at a center of the package and is referred to as a center bond package. In both types of lead bonding as mentioned above, a bond tool is used to break the lead 2 at a notch 3 forming a relatively weakest point on the lead 2. FIGS. 4 and 4A show two general bond tools having a cross groove and a dimple, respectively, provided at an end thereof. After the leads 2 are broken at the notches 3 with the bond tool, as shown in FIG. 5, separated sections of the broken leads 2 are then bonded to corresponding die pads 5 with the bond tool, as shown in FIG. 6.

[0004] While the &mgr;BGA package structure has been developed toward a form having fine pitch, a width for lead windows 1 or leads 2 provided on the &mgr;BGA package structure and a pitch between two adjacent leads 2 are correspondingly largely reduced. However, both the shape of the leads 2 and the shape and size of the notches 3 formed on the leads 2 cause considerable difficulties in production of the semiconductor package. For example, the leads 2 are usually gold-plated copper ribbons having a width of about 50 &mgr;m and a thickness of about 18 &mgr;m. When an even fine lead having a width of about 30 &mgr;m or less is employed in the semiconductor package, the forming of the notch 3 at a predetermined location on the very fine lead 2 would not only have direct influence on the quality of the formed lead 2 and the notch 3, but also on an overall rate of good yield of the substrate. For instance, a lead 2 might be so fine that it breaks before being broken at the notch 3 with a bond tool, and therefore has an adverse influence on the bonding quality that maybe obtained with the bond tool. These problems challenge the manufacturing process and the production capability of circuit board substrate manufacturers.

[0005] It is therefore desirable to work out a way to minimize the complicate procedures involved in the semiconductor package and to reduce the manufacturing cost thereof.

SUMMARY OF THE INVENTION

[0006] A primary object of the present invention is to provide an improved embossing bond tool for notching a lead in semiconductor package. The embossing bond tool is provided at an end thereof with a projected portion for vertically pressing against the lead to easily form a transverse groove thereon, so that the transverse groove forms a weak point relative to other areas on the lead for the bond tool to break the lead at the weak point before bonding the broken lead to a die pad.

[0007] Another object of the present invention is to provide an improved scissor-type bond tool for notching a lead in semiconductor package. The scissor-type bond tool has an end formed into two opposite sharp blades for horizontally cutting the lead at two lateral edges thereof to provide two symmetrical cuts, so that the two cuts form a weak point relative to other areas on the lead for the bond tool to break the lead at the weak point before bonding the broken lead to a die pad.

[0008] Difficulties in forming notches on the increasingly volume-reduced lead can therefore be avoided to enable completion of semiconductor package at simplified process, reduced cost, and upgraded rate of good yield.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

[0010] FIG. 1 schematically shows a lead in an existing &mgr;BGA package structure of the conventional semiconductor chip scale package;

[0011] FIG. 2 is a sectional view showing the location of a lead in an edge bond type of the existing &mgr;BGA package structure;

[0012] FIG. 3 is a sectional view showing the location of a lead in a center bond type of the existing &mgr;BGA package structure;

[0013] FIG. 4 shows a dimple type bond tool used in the conventional semiconductor package to break the lead for bonding purpose;

[0014] FIG. 4A shows a cross-groove type bond tool used in the conventional semiconductor package to break the lead for bonding purpose;

[0015] FIG. 5 is a top view showing that leads in the conventional semiconductor package have not yet been broken with bond tools;

[0016] FIG. 6 is a top view showing that leads in the conventional semiconductor package have been broken with bond tools and bonded to die pads;

[0017] FIG. 7 is a side view of an embossing bond tool according to a first embodiment of the present invention;

[0018] FIG. 7A is a bottom view of FIG. 7;

[0019] FIG. 8 is a side view of an embossing bond tool according to a second embodiment of the present invention;

[0020] FIG. 8A is a bottom view of FIG. 8;

[0021] FIG. 9 shows the location and the movement of the embossing bond tool of the present invention on a lead to be notched;

[0022] FIG. 10 is a top view of the lead of FIG. 9 having been notched with the embossing bond tool of the present invention;

[0023] FIG. 11 is a side view of the lead of FIG. 9 having been notched with the embossing bond tool of the present invention;

[0024] FIG. 12 is a side view of a scissor-type bond tool according to a third embodiment of the present invention;

[0025] FIG. 12A is a side view of a scissor-type bond tool according to a fourth embodiment of the present invention; and

[0026] FIG. 13 is a top view of a lead having been cut with the scissor-type bond tool of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Please refer to FIGS. 7 and 7A that are side and bottom views, respectively, of an embossing bond tool 6 according to the present invention. As shown, the embossing bond tool 6 has an end formed into a substantially flat surface 61, on which an axially projected portion 62 is diametrically extended across the flat surface 61. The projected portion 62 is raised from the flat surface 61 by a predetermined height less than a thickness of a lead 7 (see FIG. 11) to be notched. The projected portion 62 may be designed into different cross-sectional shapes, such as a rectangular shape as shown in FIG. 7, an inverted trapezoidal shape as shown in FIG. 8, a semicircular shape (not shown), or any other suitable shapes. FIG. 8A is a bottom view of FIG. 8.

[0028] Please refer to FIG. 9. By controlling the embossing bond tool 6 to a desired position over the lead 7 with the projected portion 62 extended in a direction perpendicular to a lengthwise direction of the lead 7 and a width of the lead 7 completely located within an area covered by the projected portion 62, a groove 8 transversely extended across the lead 7 and having a predetermined depth can be easily formed on the lead 7 with the embossing bond tool 6, as shown in FIGS. 10 and 11. The groove 8 forms a weak point relative to other areas on the lead 7 and can replace the conventional notch 3 to serve as a location for breaking the lead 7.

[0029] Generally, the conventional lead 2 is formed during the manufacturing process of a thin sheet of metal material. More specifically, a leadwindow 1 is formed on a thin metal sheet with a plurality of leads 2 extended across the lead window 1, as shown in FIG. 1. When the lead 2 becomes even finer from, for example, 50 &mgr;m to 30 &mgr;m or less, it would be very difficult to effectively form the notch 3 on the lead 2 at the same time of forming the lead 2. However, in the case of the embossing bond tool 6, since the groove 8 is transversely formed on the width of the lead 7, the forming of the transverse groove 8 on the lead 7 at a desired position is almost not affected by the reduced width of the lead 7. Therefore, the lead 7 can be notched without complicate procedures to reduce the manufacturing cost thereof and to enable effectively enhanced rate of good yield of semiconductor package.

[0030] Also the location of forming the notch will be exactly the same as bonding tool application point, thus simplifying the lead bonding process.

[0031] FIGS. 12 and 12A are side views of two scissor-type bond tools 9 according to the present invention. As shown, both the two scissor-type bond tools 9 have an end in the shape of an inverted letter “V” to provide two spaced sharp blades 91. By controlling either of the two scissor-type bond tools 9 to predetermined position and height relative to the lead 7 to be notched, two symmetrical cuts 10 can be formed at two lateral edges of the lead 7 with the blades 91, as shown in FIG. 13. Since the scissor-type bond tool 9 can be precisely located, it is much easier to form the cuts 10 on the lead 7 with the scissor-type bond tool 9 than to form the notch 3 on the lead 2 during manufacturing process of the thin metal sheet. Thus, the scissor-type bond tool 9 is a practicable design to cope with the problems of extremely tiny pitch between largely increased I/O pins and of manufacturing of extremely complicate circuit board.

Claims

1. A bond tool for notching a lead in semiconductor package, comprising an end formed into a substantially flat surface, and a projected portion diametrically extended across said flat surface to axially rise from said flat surface by a predetermined height; whereby by positioning and pressing said end of said bond tool having said projected portion against a lead to be notched with said projected portion transversely extended across a width of said lead, a transverse groove is formed across said lead at a predetermined position to serve as a weak point for said bond tool to break said lead at said groove before bonding said broken lead.

2. The bond tool as claimed in claim 1, wherein said projected portion has a cross section in the shape of a rectangle.

3. The bond tool as claimed in claim 1, wherein said projected portion has a cross section in the shape of an inverted trapezoid.

4. The bond tool as claimed in claim 1, wherein said projected portion has a cross section in the shape of a semicircle or any other advantageous shape.

5. The bond tool as claimed in claim 1, wherein said projected portion has a length longer than a width of said lead to be notched, so that said groove formed on said lead transversely extends a full width of said lead.

6. The bond tool as claimed in claim 1., wherein the location of forming the notch will be exactly the same as bonding tool application point, thus simplifying the lead bonding process

7. A bond tool for notching a lead in semiconductor package, comprising an end in the shape of an inverted letter “V” to provide two spaced sharp blades, said blades being adapted to form two symmetrical cuts at predetermined positions on two lateral edges of a lead to be notched, whereby said two symmetrical cuts serve as a weak point for said bond tool to break said lead thereat before bonding said broken lead.