WO2009008839A1

WO2009008839A1 - Die ejector with illuminating unit

Info

Publication number: WO2009008839A1
Application number: PCT/SG2008/000241
Authority: WO
Inventors: Yong Joo Puah; Johann Joset Brunner
Original assignee: Generic Power Pte Ltd
Priority date: 2007-07-09
Filing date: 2008-07-08
Publication date: 2009-01-15
Also published as: SG148902A1

Abstract

The invention provides a die ejector (300) and a method for die alignment and ejection using said die ejector (300) during semiconductor packaging process. The die ejector (300) comprises an ejector housing (320), a needle holder (340), a plurality of ejector needles (360), and an illuminating unit (370). The illuminating unit (370), attached to the ejector housing (320), comprises a plurality of light sources (372) and a light reflective coating (374). The light emitted by the light sources (372) is directed by the light reflective coating (374) towards the lower side of a wafer (307) disposed on an adhesive film (303) above a wafer table (304). The image of the illuminated wafer (307) is captured by a vision inspection unit (480) located above the wafer (307), and is used for adjusting the position and orientation of the wafer before die ejection.

Description

DIE EJECTOR WITH ILLUMINATING UNIT

Field of the Invention

[0001] The present invention generally relates to an apparatus for semiconductor chip processing, and in particular to a die ejector having an illuminating unit.

Background of the Invention

[0002] The semiconductor manufacturing process comprises four major steps: materials preparation, crystal growth and wafer preparation, wafer fabrication, and packaging. In the packaging step, a wafer is first mounted onto a transparent adhesive film stretched out on a wafer ring, and separated into individual dies by scribing or sawing. After singulation, the wafer, with the individual dies held in place on the adhesive film, is disposed on a wafer table of a die bonder apparatus, where the dies are subsequently picked up from the adhesive film by a Pick-and-Place mechanism for further processing.

[0003] To facilitate effective removal of the dies from the adhesive film, the die bonder apparatus has a die ejector beneath the wafer table for ejecting the individual dies from the adhesive film before the dies are picked up by the Pick-and-Place mechanism. FIG. IA and IB show a perspective view and a cross-sectional view of a conventional die ejector respectively. The conventional die ejector 100 comprises an ejector housing 120 mounted on a support base 101, a needle holder 140 housed in the ejector housing 120, and a single or a plurality of ejector needles 160 disposed on the needle holder 140. Details of the ejector housing 120 are provided in FIG. 2. FIG. 2A shows a side view of the ejector housing; FIG. 2B a cross-sectional view; and FIG. 2C a top plan view. The ejector housing 120, normally a single piece made of metal, has a cylindrical shaft 122 that defines a hollow inner chamber 123, and a circular top surface 132 that has a plurality of grooves 133 and associated holes 134 extending through the thickness of the top surface 132. Now referring back to FIG. IB, each ejector needle 160 on the needle holder 140 is configured to be in alignment with each hole 134 on the top surface 132 of the ejector housing 120. The needle holder 140 together with the ejector needles 160 is operable to be raised or lowered with respect to the ejector housing 120. [0004] Before the conventional die ejector ejects a die, the die bonder apparatus further has an alignment system for inspecting and adjusting the position and orientation of the die. FIG. 3A and 3B show diagrams of a conventional alignment system 200 and its cooperation with the conventional die ejector 100 in semiconductor chip processing. The conventional alignment system 200 comprises a plurality of light sources 272, only two shown as 272a and 272b in FIG. 3, for illuminating the dies 102 a, 102b, 102c on the transparent adhesive film 103 supported by the wafer table 104 (not shown in FIG. 3), a vision inspection unit 280 for capturing the image of the exposed dies 102 a, 102b, 102c and optionally processing the captured image, and a control unit 290 (not shown in FIG. 3) for receiving and processing the information from the vision inspection unit 280 and sending instructions to move the wafer table 104 in a horizontal plane so that the center die 102b indexed to be ejected is well aligned with the center of the die ejector 100. The light sources 272a, 272b and the vision inspection unit 280 are both located above the wafer table 104, opposite to the die ejector 100. When the alignment is achieved, the needle holder 140 and the ejector needles 160 are raised with respect to the ejector housing 120. In the raised position, each ejector needle 160 projects through the corresponding hole 134 by a pre-determined amount and ejects the die 102b off the adhesive film 103.

[0005] FIG. 4 A shows a typical grey scale image of dies 102 captured by the vision inspection unit 280 and processed by the control unit 290, when the conventional die ejector 100 and alignment system 200 as shown in FIG. 3 are in operation. In the image, the exposed die surface is shown as white square; solder balls 105 deposited on the exposed die surface in grey scale; and saw streets 106 as sharp dark lines between every two adjacent dies 102. The information of the saw streets 106 extracted from the processed image can be used by the control unit 290 to indicate the position and orientation of the die 102, and to calculate and determine the movement of the wafer table 104 (not shown in FIG. 4) for alignment.

[0006] However, with the wide use of protective coating on the die surface to protect the die against unexpected damage due to more complicated semiconductor chip manufacturing process, a problem arises in relation to the die alignment based on the information of saw streets. Because most of the protective coating chemicals, such as Hysol, have a dark color, the contrast between the saw streets and the dies in the captured image is dramatically reduced. FIG. 4B shows a typical grey scale image of dies 102 coated with protective coating Hysol, captured and processed by the same vision inspection unit 280 and control unit 290 used for FIG. 4A. The contrast between the dies 102 and the saw streets 106 is reduced to the extent that it is impossible for the control unit 290 to precisely recognize the saw streets 106 for die alignment before ejection. [0007] In view of the above-mentioned problem, a new generation of die ejector and/or alignment system is required.

Summary of the Invention

[0008] In order to address the problem associated with the prior art, the present invention provides a die ejector with an integrated illuminating unit. [0009] According to one aspect of the invention, there is provided a die ejector for semiconductor chip processing, the die ejector comprising an ejector housing having a shaft and a translucent cap mounted on the shaft, wherein the cap has a sidewall and a planar top surface with a plurality of holes that extend through the thickness of the top surface; a needle holder housed in the ejector housing; a plurality of ejector needles disposed on the needle holder, each aligned with one hole of the cap; and an illuminating unit having a plurality of light sources attached to the cap, and a light reflective coating applied to the inner surface of the cap; wherein the needle holder together with the plurality of ejector needles is operable to be raised or lowered with respect to the ejector housing, so that in the raised position, each ejector needle projects through the hole of the cap by a pre-determined amount, and wherein the light reflective coating is operable to reflect the light emitted by the plurality of light sources towards the top surface of the cap.

[0010] According to another aspect of the invention, there is provided an ejector housing for semiconductor die processing, the ejector housing comprising a shaft having a hollow inner chamber for housing a needle holder and a plurality of ejector needles, wherein the needle holder together with the ejector needles is operable to be raised or lowered with respect to the shaft; and a translucent cap mounted on top of the shaft, the cap comprising a sidewall having interconnection means for connecting with a plurality of light sources; a top surface having a plurality of holes extending through the thickness of the top surface, wherein each hole is aligned with each of the ejector needles, so that when the needle holder is raised with respect to the shaft, the ejector needles project through the holes over the top surface of the cap; and a light reflective coating on the inner surface of the cap.

[0011] According to yet another aspect of the invention, there is provided a method for die alignment and ejection in semiconductor chip processing, the method comprising the steps of: disposing a singulated wafer held on an transparent adhesive film onto a wafer table; moving the wafer table for indexing a die to a pre-determined location where a die ejector with an integrated illuminating unit is located beneath the wafer table in alignment with a vision inspection unit located above the wafer table; illuminating the wafer from beneath by the illuminating unit of the die ejector; capturing the image of the singulated wafer by the vision inspection unit and transferring the captured image to a connected control unit; processing the received image by the control unit, determining the position and orientation of the dies based on the information of the exposed saw streets and calculating the movement of the wafer table in order to align the die to be ejected with the die ejector; sending instructions by the control unit to move the wafer table according to the calculation; and raising the needle holder and ejector needles of the die ejector, thereby ejecting the die from the adhesive film.

[0012] The objectives and advantages of the present invention will become apparent from the following detailed description of embodiments thereof in connection with the accompanying drawings.

Brief Description of the Drawings

[0013] Preferred embodiments according to the present invention will now be described with reference to the Figures accompanied herein, in which like reference numerals denote like elements.

[0014] FIG. IA and IB show a perspective view and a cross-sectional view of a conventional die ejector respectively. [0015] FIG. 2A shows a side view of an ejector housing of the conventional die ejector shown in FIG. 1; FIG. 2B a cross-sectional view; and FIG. 2C a top plan view. [0016] FIG. 3 A and 3B show diagrams of a conventional alignment system in cooperation with the conventional die ejector shown in FIG. 1 in semiconductor chip processing.

[0017] FIG. 4A shows a grey scale image of an uncoated die captured by a vision inspection unit and processed by a control unit of the conventional alignment system shown in FIG. 3, whilst FIG. 4B shows a grey scale image of a die with surface protective coating.

[0018] FIG. 5 A shows a perspective view of a die ejector having an illuminating unit in accordance with one embodiment of the present invention whilst FIG. 5B shows a cross-sectional view of the upper part of the die ejector.

[0019] FIG. 6A shows a perspective views of the cap of the ejector housing as shown in FIG. 5; FIG. 6B a side view; FIG. 6C a top view; FIG. 6D a bottom view; and 6E a cross-sectional view.

[0020] FIG. 7A shows an exploded view of a subassembly of the ejector housing and the illuminating unit as shown in FIG. 5 whilst FIG. 7B shows a partially broken away front perspective view of the cap, illustrating the surface to which the light reflective coating is applied.

[0021] FIG. 8 shows a cross sectional view the die ejector with illuminating unit as shown in FIG. 5, illustrating the optical path of the light emitted by the light sources and reflected by the light reflective coating.

[0022] FIG. 9A and 9B show diagrams of an alignment system in cooperation with the die ejector as shown in FIG. 5 in semiconductor chip processing, in accordance with one embodiment of the present invention.

[0023] FIG. 1OA shows a grey scale image captured by the vision inspection unit and processed by the control unit of the alignment system as shown in FIG. 9 during the semiconductor chip processing in cooperation with the die ejector; whilst FIG. 1OB shows an image obtained by the same system except that the die ejector is without the light reflective coating.

Detailed Description of the Invention [0024] The present invention may be understood more readily by reference to the following detailed description of certain embodiments of the invention.

[0025] Now referring to FIG. 5, there is provided a die ejector having an illuminating unit in accordance with one embodiment of the present invention. FIG. 5A shows a perspective view of the die ejector 300; FIG. 5B shows a cross-sectional view of the upper part of the die ejector 300. The die ejector 300 comprises an ejector housing

320, an illuminating unit 370 attached to the ejector housing 320, a needle holder 340 housed in the ejector housing 320, and a single or a plurality of ejector needles 360 disposed on the needle holder 340. The ejector needles 360 and needle holder 340 are identical to those in the conventional die ejectors 100 as shown in FIG. 1.

[0026] The ejector housing 320 comprises a shaft 321 mounted on a support base

301, and a translucent cap 331 disposed on top of the shaft 321. The shaft 321 has a cylindrical body 322 defining a hollow inner chamber 323 for housing the ejector needles

360 and needle holders 340, a cap resting shoulder 324 and a cylindrical nose 325 fitting into an inner chamber 339 of the cap 331. The cap 331 has a circular top surface 332, and a sidewall 335 with a step-tapered cylindrical outer surface, defining a hollow inner chamber 339. The cap 331 will be described in greater detail further below.

[0027] In accordance with one embodiment of the cap, the translucent cap 331 is transparent. In accordance with another embodiment of the cap, the translucent cap 331 is made of plastic. In accordance with yet another embodiment of the cap, the translucent cap 331 is made of Engineering Plastic Stock Shapes with Static Dissipative (ESD)

Properties.

[0028] In accordance with another embodiment of the ejector housing, the ejector housing 320 further comprises a cover 310, disposed on top of the cap 331 for protection against dirt and damage when the die ejector 300 is not in use.

[0029] Still referring to FIG. 5, the illuminating unit 370 comprises a plurality of light sources 372 attached to the sidewall 335 of the cap 331, and a light-reflective coating 374 applied to the inner surface of the cap 331. The light sources 372 are electronically connected to a power through wires. The detailed features of the illuminating unit 370 will be described later. [0030] Now referring to FIG. 6, there are provided details of the cap 331 as shown in FIG. 5. FIG. 6A shows a perspective views of the cap 330; FIG. 6B a side view; FIG. 6C a top view; FIG. 6D a bottom view; and 6E a cross-sectional view. The top surface 332 is provided with a network of grooves 333 and holes 334, the configuration of which are identical to those carved on the top surface 132 of the conventional ejector housing 100 as shown in FIG. 1. The lower portion of the sidewall 335 has two resting shoulders 336a, 336b on the outer surface for supporting the cover 310 (not shown in FIG. 6), interconnection means 337a for mounting the cap 331 onto the shaft 321 and an aperture 337b for housing the wires connecting the light sources 372 to the power. The upper portion of the sidewall 335 has an array of recesses 338 on the outer surface for housing the plurality of light sources 372. The dimension of the recesses 338 is configured to fit the outer contour of the light sources 372 disposed within. [0031] In one embodiment of the recesses, the recesses 338 are cylindrical in shape.

[0032] Now referring to FIG. 7, there are provided details of a subassembly of the ejector housing 320 and the illuminating unit 370 as shown in FIG. 5. FIG. 7 A shows an exploded view of the subassembly; FIG. 7B a partially broken away front perspective view of the cap 331, illustrating the surface to which the light reflective coating 374 is applied. The cap 331 is secured to the shaft 321 by the pair of interconnection means 337a (not shown in FIG. 7) and 327a. The light sources 372 are disposed in the recesses 338 of the cap 331 and positioned in such a way that most of the light emitted from the light sources 372 will be delivered towards the top surface 332 of the cap 331 either directly or after being reflected by the light reflective coating 374. The wires connecting the light sources 372 to the power is disposed in the passage formed by the aligned apertures 337b and 327b.

[0033] In accordance with one embodiment of the present invention, each light source 372 is positioned in a vertical orientation, emitting light towards the top surface 332 of the cap 331. In accordance with another embodiment, each light source 372 is positioned in a horizontal orientation, emitting light towards the inner chamber 339 of the cap 331.

[0034] The light sources 372 may be any type that is of proper size to be attached to the cap 331 and of sufficient light intensity for illumination. In accordance with one embodiment of the light sources, the light sources 372 are light emitting diode (LED). In accordance with another embodiment, the light sources comprise optical fibers. [0035] The light reflective coating 374 is applied to the inner surface of the cap

331 as shown in FIG. 7B, effective to specularly reflect the light from the light sources 372 so as to direct the light towards the top surface 332 of the cap 331. And the light reflective coating may be applied for multiple layers to increase the coating thickness for higher light reflectance.

[0036] In one embodiment of the light reflective coating, the light reflective coating 374 comprises aluminum. In another embodiment, the light reflective coating 374 is metallic. In yet another embodiment, the light reflective coating 374 comprises white pigments mixed in a synthetic binder resin. In one embodiment of the white pigment, the white pigment is barium sulfate. In another embodiment, the white pigment is titanium dioxide. In yet another embodiment, the light reflective coating consists of both barium sulfate and titanium as white pigments.

[0037] Now referring to FIG. 8, there is provided a cross-sectional view of the die ejector 300 as shown in FIG. 5, illustrating the optical path of the light emitted by the light sources 372 and reflected by the light reflective coating 374 in accordance with one embodiment of the present invention. The open arrows denote the emitted light whilst the close arrows the reflected light. The light sources 372 disposed in the recesses are in a horizontal orientation, emitting light towards the inner chamber 339 of the cap 331. The light transmits though the translucent sidewall 335 of the cap 331 and strikes the light reflective coating 374 on the inner surface of the cap 331, where the light is reflected and directed towards the top surface 332. The reflected light is subsequently transmits through the translucent top surface 332 of the cap 331 and the transparent adhesive film 303 (not shown in FIG. 8), and strikes the lower side of the singulated wafer 307 (not shown in FIG. 8). Most of the light is then reflected or absorbed by the die surface or the protective coating on the die surface, whilst the rest of the light goes through the saw streets 306 between the dies 302 and transmits further upward.

[0038] Now referring to FIG. 9A and 9B, there are provided diagrams of the die ejector 300 in cooperation with an alignment system in semiconductor chip processing, in accordance with one embodiment of the present invention. The die ejector with an illuminating unit 300 has the identical configuration to that of the earlier embodiment shown in FIG. 5. The alignment system 400 comprises a vision inspection unit 480 and a control unit 490, but not any light sources as shown in FIG. 1. The vision inspection unit and the control unit have identical features as those in the conventional alignment system 100 shown in FIG. 3. The die ejector with an illuminating unit 300 is located beneath the wafer table 304, whilst the vision inspection unit 480 is located on the opposite site of the wafer stable 304 in alignment with the die ejector 300. In operation, a singulated wafer 307 on an adhesive film 303 is input onto the wafer table 304 (not shown in FIG. 9). The plurality of light sources 372 emit light, providing bottom lighting. Most of the emitted light is directed towards the top surface 332 of the cap 331 by the light reflective coating 374, thereby illuminating the dies 302 a, b, c positioned above the ejector housing 320. The vision inspection unit 480 captures the image of the exposed dies 302a, 302b, 302c and transfers the information to the remote connected control unit 490 (not shown in FIG. 9). Based on the processed information of the position and orientation of the saw streets 306 embodied in the captured image, the control unit 490 sequentially instructs the wafer table 304 to align the center die 302b with the die ejector 300 at the pre-determined picking location, and the die ejector 300 to raise the ejector needle 360 in order to lift the die 302b off the adhesive film 303.

[0039] FIG. 1OA shows a grey scale image captured by the vision inspection unit

480 and processed by the control unit 490 of the alignment system as shown in FIG. 9 during the semiconductor chip processing in cooperation with the die ejector 300; whilst FIG. 1OB shows an image obtained by the same system except that the light reflective coating 374, in this case Nippon paint 102, is not applied to the cap 331. For easy interpretation, grey values of the image are rated from 0 to 255; with 0 and 255 corresponding to the lowest and highest light intensity respectively. When the grey values of the dies 302 in FIG. 1OA and B are adjusted to the same grey value 16, the saw streets 306, visualized as open space between the adjacent dies 302, have dramatically different grey values, 255 for FIG. 1OA whilst 100 for FIG. 1OB. The higher grey value of the saw streets 306 in the captured image in FIG. 1OA indicates a sharper contrast between the dies 302 and the saw streets 306 when the light reflective coating 374 is applied to the cap 331 of the ejector housing 320 as shown in FIG. 7B. The improved contrast contributes to more precise information of the position and orientation of dies 302 being extracted by the control unit 490 (not shown in FIG. 10) to orchestrate the die alignment and ejection.

[0040] While the present invention has been described with reference to particular embodiments, it will be understood that the embodiments are illustrative and that the invention scope is not so limited. Alternative embodiments of the present invention will become apparent to those having ordinary skill in the art to which the present invention pertains. Such alternate embodiments are considered to be encompassed within the spirit and scope of the present invention. Accordingly, the scope of the present invention is described by the appended claims and is supported by the foregoing description.

Claims

1. A die ejector for semiconductor chip processing, the die ejector comprising: an ejector housing having a shaft and a translucent cap mounted on the shaft, wherein the cap has a sidewall and a planar top surface with a plurality of holes that extend through the thickness of the top surface; a needle holder housed in the ejector housing; a plurality of ejector needles disposed on the needle holder, each aligned with one hole of the cap; and an illuminating unit having a plurality of light sources attached to the cap, and a light reflective coating applied to the inner surface of the cap; wherein the needle holder together with the plurality of ejector needles is operable to be raised or lowered with respect to the ejector housing, so that in the raised position, each ejector needle projects through the hole of the cap by a pre-determined amount, and wherein the light reflective coating is operable to reflect the light emitted by the plurality of light sources towards the top surface of the cap.

2. The die ejector of claim 1, wherein the translucent cap is transparent.

3. The die ejector of claim 1, wherein the cap is made of plastic.

4. The die ejector of claim 1, wherein the cap is made of ESD materials.

5. The die ejector of claim 1, wherein the plurality of light sources are LED.

6. The die ejector of claim 1, wherein the plurality of light sources are attached to the sidewall of the cap.

7. The die ejector of claim 6, wherein the sidewall of the cap has a plurality of recesses for holding the plurality of light sources.

8. The die ejector of claim 7, wherein each light source is disposed in one recess with a horizontal orientation, emitting light towards the inner surface of the cap.

9. The die ejector of claim 7, wherein each light source is disposed in one recess with a vertical orientation, emitting light towards the top surface of the cap.

10. The die ejector of claim 1, wherein the light reflective coating comprises white pigments mixed in a synthetic binder resin.

11. The die ejector of claim 10, wherein the white pigment comprises barium sulfate.

12. The die ejector of claim 10, wherein the white pigment comprises titanium dioxide.

13. The die ejector of claim 1, wherein the light reflective coating comprises aluminum.

14. The die ejector of claim 1, wherein the light reflective coating is metallic reflection plate.

15. An ejector housing for semiconductor die processing, the ejector housing comprising: a shaft having a hollow inner chamber for housing a needle holder and a plurality of ejector needles, wherein the needle holder together with the ejector needles is operable to be raised or lowered with respect to the shaft ; a translucent cap mounted on top of the shaft, the cap comprising: a sidewall having interconnection means for connecting with a plurality of light sources; a top surface having a plurality of holes extending through the thickness of the top surface, wherein each hole is aligned with each of the ejector needles, so that when the needle holder is raised with respect to the shaft, the ejector needles project through the holes over the top surface of the cap; and a light reflective coating on the inner surface of the cap.

16. The ejector housing of claim 15, wherein the translucent cap is transparent.

17. The ejector housing of claim 15, wherein the cap is made of plastic.

18. The ejector housing of claim 15, wherein the cap is made of ESD materials.

19. The ejector housing of claim 15, wherein the light reflective coating comprises white pigments mixed in a synthetic binder resin.

20. The die ejector of claim 19, wherein the white pigment comprises barium sulfate.

21. The die ejector of claim 19, wherein the white pigment comprises titanium dioxide.

22. The die ejector of claim 15, wherein the light reflective coating comprises aluminum.

23. The die ejector of claim 15, wherein the light reflective coating is metallic reflection plate.

24. A method for die alignment and ejection in semiconductor chip processing, the method comprising the steps of: disposing a singulated wafer held on an transparent adhesive film onto a wafer table; moving the wafer table for indexing a die to a pre-determined location where a die ejector is located beneath the wafer table in alignment with a vision inspection unit located above the wafer table, wherein the die ejector comprises: an ejector housing having a shaft and a translucent cap mounted on the shaft, wherein the cap has a sidewall and a planar top surface with a plurality of holes that extend through the thickness of the top surface; a needle holder housed in the ejector housing; a plurality of ejector needles disposed on the needle holder, each aligned with one hole of the cap; and an illuminating unit having a plurality of light sources attached to the sidewall of the cap, and a light reflective coating applied to the inner surface of the cap; wherein the needle holder together with the plurality of ejector needles is operable to be raised or lowered with respect to the ejector housing, so that in the raised position, each ejector needle projects through the hole of the cap by a predetermined amount, and wherein the light reflective coating is operable to reflect the light emitted by the plurality of light sources towards the top surface of the cap; illuminating the wafer from beneath by the illuminating unit of the die ejector; capturing the image of the singulated wafer by the vision inspection unit and transferring the captured image to a connected control unit; processing the received image by the control unit, determining the position and orientation of the dies based on the information of the exposed saw streets and calculating the movement of the wafer table in order to align the die to be ejected with the die ejector; sending instructions by the control unit to move the wafer table according to the calculation; and raising the needle holder and ejector needles of the die ejector, thereby ejecting the die from the adhesive film.