Laser-assisted deposition with beam shaping

Abstract

To provide laser-assisted deposition with beam shaping for significantly increasing the throughput for LAD applications, and for SMT-pad deposition and wafer-bumping applications.SOLUTION: Laser-assisted deposition is improved by shaping a laser beam before a deposition tape is irradiated with the laser beam. The beam is shaped to irradiate a larger area of the deposition tape than is possible with an unshaped laser beam spot. Preferably, this larger area corresponds to the smallest SMT pad to be formed on a workpiece, and other larger SMT pads can be formed by additively combining such deposits. The laser energy may be more economically used by distributing it about a greater irradiation area than the known unshaped laser beam spot.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a laser-assisted deposition apparatus, a method for forming features on a workpiece by depositing a deposition medium from a tape onto the workpiece, and a method for performing wafer bumping to form bumps or balls of a deposition medium on a workpiece in a regularly-pitched array. [Background technology]

[0002] Laser assisted deposition (LAD) is a developing technology for depositing adhesive materials, particularly solder paste, onto a workpiece or substrate, and may be considered as an alternative to conventional paste deposition techniques such as stencil or screen printing (hereafter referred to as "screen printing" for convenience). For convenience, the following description will refer solely to the deposition of paste, but it should be understood that other adhesive materials may be deposited in a similar manner. The LAD process features the use of a flexible tape having paste applied to one side thereof. A laser is directed to illuminate an area of ​​the opposite, i.e., uncoated, side of the tape, thereby causing a small amount of paste to be extruded from the coated side coincident with the illuminated area. The extruded amount of paste may then land at an aligned target location on the workpiece. Such an approach has various advantages over conventional screen printing processes. - Because the amount of paste extruded from the tape is controlled through the use of a laser, the paste deposited can be more precisely controlled in smaller amounts than with screen printing. - It is more easily possible to deposit additional paste onto a previously deposited target, meaning that the height of the paste deposit can be precisely controlled. - Various materials can be deposited onto the same target area. - Material can be added to a previously printed substrate, for example to make up for any deficiencies resulting from the printing process.

[0003] A typical LAD apparatus 1 for use in depositing solder paste 3 from a deposition tape 2 onto a workpiece W is shown diagrammatically from the side in FIG. 1. The aforementioned deposition tape 2 is typically a flexible plastic material, such as polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyimide (PI) or flexible glass, or a composite of two or more such materials, such as a multi-layer material. The deposition tape 2 may be stored on a deposition tape storage reel 4 before being coated with the solder paste 3. Before deposition, the deposition tape 2 is mounted on a used tape reel 5, which is driven in rotation to advance the deposition tape 2, so that the drive of the used tape reel 5 causes the deposition tape 2 to unwind from the deposition tape storage reel 4 and wind onto the used tape reel 5. Various rollers 6 may be used to define the deposition tape path and to provide tension for the deposition tape 2. In particular, two rollers 6A, 6B are used to maintain an area of ​​the deposition tape 2 close to and parallel to the top surface of the workpiece W. A laser source 7, which may include various types of laser sources, such as, for example, Nd:YAG laser sources, Nd:YLF laser sources, Nd:YVO4 laser sources, Nd:GdVO4 laser sources, Yb:YAG laser sources, Er:YAG laser sources, Er:Cr:YSGG laser sources, Er:YSGG laser sources, and Gd:WO4 laser sources, is positioned above this area and aligned to generate a laser beam 8 that is directed to a spot on the top surface of the deposition tape 2 between the rollers 6A and 6B, i.e., to an "illumination area" on the top main surface of the deposition tape 2. The illumination laser beam passes through the deposition tape 2 and is transmitted to its underside. The workpiece W and the laser source 7 are relatively movable in the horizontal (XY) plane so that a desired deposition pattern can be created on the workpiece W. Typically, the laser source 7 is moveable in the XY plane by a two-axis galvanometer arrangement (not shown) while the workpiece W is supported on a platform 16 which is held stationary. Alternatively, the laser source 7 may be held stationary while the workpiece W platform 16 is moveable in the XY plane by such a galvanometer arrangement.A further alternative is to have both the laser source 7 and the workpiece platform 16 travel in the XY plane to achieve relative movement.

[0004] The underside of the deposition tape 2 is coated with solder paste 3 using a coating tape 9 fed from a coating tape storage reel 10 to a coating tape used reel 11 which is rotatable and advances said coating tape 9. The coating tape 9 may comprise a flexible plastic material and may advantageously be of similar construction to the deposition tape 2, except that the deposition tape 2 is provided with a hydrophilic surface and the coating tape is provided with a hydrophobic surface. The coating tape 9 and the deposition tape 2 are diverted to a pasting area 12 formed between respective rollers 13 and 14, in which there is a very narrow gap between the coating tape and the underside of the deposition tape 2. The solder paste 3 is released from a paste distributor 15 into the pasting area 12, such that a mass of solder paste 3 is formed between the rollers 13 and 14. As the deposition tape 2 and coating tape 9 pass through the pasting area 12, the hydrophilic underside of the deposition tape 2 is coated with solder paste 3, the thickness of the coating being controlled by the distance between rollers 13 and 14, while the hydrophobic surface of the coating tape 9 remains substantially free of paste. Of course, "hydrophobic" and "hydrophilic" properly apply to aqueous fluids rather than flux-based fluids such as solder paste, although in practice solder paste exhibits similar wetting properties.

[0005] The laser beam transmitted through the deposition tape is absorbed by the paste 3 coated on the lower surface of the deposition tape 2, and the paste is extruded from the lower surface of the deposition tape 2 at the absorption locations by the laser beam as described above.

[0006] However, a problem exists with such known devices in that because a laser is used to achieve the deposition, the throughput is much lower than with screen printing. Current LAD machines use a single point laser to project the deposition medium from the deposition tape onto the workpiece. The throughput of the machine is then limited by the speed of the two-axis galvanometer and the X, Y axis platform 16 on which the workpiece W being processed is mounted. Summary of the Invention [Problem to be solved by the invention]

[0007] Although the present invention aims to provide an apparatus and method for significantly increasing throughput in LAD applications, particularly for SMT pad deposition and wafer bumping applications, it is believed that the techniques of the present invention may also be applied more broadly and aid throughput in a variety of applications. [Means for solving the problem]

[0008] According to the invention, this object is achieved by shaping the laser beam before it irradiates the deposition tape. In a first embodiment, the beam is shaped to irradiate a larger area of ​​the deposition tape than would be possible with an unshaped laser beam spot. This larger area preferably corresponds to the smallest SMT pad to be formed on the workpiece, and other larger SMT pads can be formed by additively combining such deposits. In a second embodiment, the beam is split into a number of sub-beams, each of which can be used to form a bump or ball of deposition medium, realizing a significantly increased throughput for wafer bumping applications. In either case, the invention exploits the fact that the energy provided by the laser source is greater than the energy required to achieve the deposition, and thus the laser energy can be used more economically by distributing it around a larger irradiation area than with the known unshaped laser beam spot.

[0009] As used herein, the term "beam shaping" is used to refer to an optical process in which the laser beam energy is controllably distributed about a larger area in a plane perpendicular to the optical path of the laser beam.

[0010] In particular, a beam shaper ideally adapted for use in the present invention may be a diffractive optical element (DOE), or a spatial light modulator (SLM), such as an electrically addressable spatial light modulator (EASLM), each of which components are well known in themselves and need not be described further here. However, because a DOE functions by diffracting incident light, whereas an SLM functions by refracting incident light, these elements may also be referred to as "diffractive / refractive beam shapers".

[0011] According to a first aspect of the invention, there is provided a laser assisted deposition apparatus for depositing a deposition medium from a tape onto a workpiece to form a feature on the workpiece, the tape having upper and lower major surfaces, the lower major surface being coated with the deposition medium, the laser assisted deposition apparatus comprising: a tape advancement mechanism for moving a tape through the laser assisted deposition apparatus along a moving path; a laser source operable to direct a laser beam along an optical path toward the top major surface of the tape at an illumination area thereof; a workpiece support for supporting the workpiece proximate the lower major surface such that a deposition medium disposed on the lower major surface and coincident with the illumination area can be ejected from the lower major surface onto the workpiece when a laser beam is directed toward the illumination area; a beam shaper disposed in the optical path to create an illumination pattern in the illumination area; A laser assisted deposition apparatus is provided comprising:

[0012] According to a second aspect of the invention there is provided a method of forming a feature on a workpiece by depositing a deposition medium from a tape onto the workpiece, comprising the steps of: i) providing the tape having an upper major surface and a lower major surface, the lower major surface being coated with the deposition medium; ii) providing a laser assisted deposition apparatus having a laser source; iii) supporting the workpiece adjacent the lower major surface; iv) advancing the tape along a travel path through said laser assisted deposition apparatus; v) directing a laser beam from a laser source along an optical path toward an upper major surface of the tape at an irradiated area thereof, such that a deposition medium disposed on a lower major surface thereof and coincident with the irradiated area thereof is emitted from the lower major surface onto the workpiece; Including, Step v) includes shaping a laser beam to create an illumination pattern in an illumination area. A method is provided.

[0013] According to a third aspect of the present invention, there is provided a method of performing wafer bumping to form bumps or balls of deposition medium on a workpiece in a regular pitch array, the method comprising the steps of: i) providing a tape having an upper major surface and a lower major surface, said lower major surface being coated with a deposition medium; ii) providing a laser assisted deposition apparatus having a laser source; iii) supporting the workpiece adjacent the lower major surface; iv) advancing the tape through the laser assisted deposition apparatus along a travel path; v) directing a laser beam from a laser source along an optical path towards a beam shaper, the beam shaper splitting the laser beam into a plurality of spatially separated sub-beams; vi) directing the plurality of spatially separated sub-beams at a top major surface of a tape to form an illumination pattern in the illumination area thereof, and a deposition medium disposed on a bottom major surface thereof and coincident with the illumination pattern is ejected from the bottom major surface onto a workpiece; A method is provided, comprising:

[0014] Other specific aspects and features of the present invention are set forth in the accompanying claims.

[0015] The invention will now be described with reference to the accompanying drawings (not to scale). [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic side view of a known laser-assisted deposition (LAD) apparatus. [Diagram 2] 1 is a schematic side view of a laser-assisted deposition (LAD) apparatus according to one embodiment of the present invention; [Figure 3A] FIG. 2 is a schematic view from above of a workpiece with intended SMT pad locations. [Figure 3B] 3B is a schematic diagram from above of the workpiece of FIG. 3A with the corresponding position of the laser beam spot illustrating the operation of the known LAD apparatus. [Figure 3C] 3B is a schematic diagram from above of the workpiece of FIG. 3A with the corresponding position of the laser beam pattern illustrating the operation of the LAD apparatus of FIG. 2. [Figure 4] 1 is a schematic top view of a workpiece undergoing a wafer bumping process. [Figure 5A] 5 is a schematic top view of the workpiece of FIG. 4 during a stage of a wafer bumping process in accordance with one embodiment of the present invention. [Figure 5B] 5 is a schematic top view of the workpiece of FIG. 4 during a stage of a wafer bumping process in accordance with one embodiment of the present invention. [Figure 5C]5 is a schematic top view of the workpiece of FIG. 4 during a stage of a wafer bumping process in accordance with one embodiment of the present invention. [Figure 6A] 5 is a schematic top view of the workpiece of FIG. 4 during a stage of a wafer bumping process in accordance with another embodiment of the present invention. [Figure 6B] 5 is a schematic top view of the workpiece of FIG. 4 during a stage of a wafer bumping process in accordance with another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] FIG. 2 shows, from a side view, a schematic representation of a laser-assisted deposition (LAD) apparatus 20 according to an embodiment of the invention. The apparatus 20 obviously has many similarities with the known apparatus 1 of FIG. 1, and components common to both have retained their original numbering, and a full description of their function does not need to be repeated here. However, importantly, the apparatus 20 includes a beam shaper 21, which is arranged in the optical path of the laser beam 8 emitted by the laser source 7 before the laser beam reaches the deposition tape 2. The beam shaper 21 shapes said laser beam 8, so that a shaped laser beam 8' is generated, which illuminates the deposition tape 2. The said shaped laser beam 8' creates, in the illumination area of ​​the deposition tape 2, an illumination pattern corresponding to the cross-sectional profile of the shaped laser beam 8'. As mentioned before, the beam shaper 21 is preferably a diffractive / refractive beam shaper, more preferably a DOE or an SLM, such as an EASLM. The beam shaper 21 may be held in place by any suitable mounting mechanism (not shown).

[0018] Various exemplary modes of operation of device 20 will now be described.

[0019] 3A-3C depict a process for forming features in the form of SMT pads on a workpiece W. Fig. 3A shows, for purposes of illustration only, a schematic view from above of the workpiece W having intended SMT pad locations, including four relatively small SMT pad locations 22 and one relatively large SMT pad location 23. To create the pads, a LAD apparatus may be used to deposit a deposition medium onto these locations.

[0020] FIG. 3B shows the workpiece W of FIG. 3A from above, with the corresponding positions of the "spot deposits" 24 illustrating the operation of the known LAD apparatus 1. As shown, using the known LAD apparatus 1 of FIG. 1, each relatively small SMT pad is formed by depositing six spot deposits 24 of deposition medium in a 2×3 matrix, while the relatively large SMT pad is formed by depositing 24 such spot deposits 24 in a 4×6 matrix. Each individual spot deposit 24 is formed by irradiating an irradiated area of ​​the deposition tape 2 with an unshaped beam 8 such that a very small amount of deposition medium is forced out of the deposition tape 2, resulting in the formation of the small "spot deposits" 24. In total, using this known process, the workpiece W requires 48 spot deposits 24. Since only one spot deposit 24 can be formed at a time, this requires that 48 times the workpiece W is moved relative to the irradiated area of ​​the deposition tape 2 on which it is deposited and then ready for the next deposition. Naturally, the individual spot deposits 24 will coalesce and spread across the SMT pad locations 22 and 23 during the subsequent reflow process.

[0021] FIG. 3C shows the workpiece W of FIG. 3A from above, with the corresponding position of the laser beam pattern showing the operation of the LAD apparatus 20 of FIG. 2. Here, a beam shaper 21, such as a DOE, is used to generate a substantially rectangular irradiation pattern and generate a shaped laser beam 8' having a shape and size that matches the SMT pad, advantageously and as shown in FIG. 3C, the smallest SMT pad to be formed on the workpiece W. Thus, the irradiation pattern is tailored to specific dimensions to create a shaped deposit 25 on the workpiece W, which substantially fills the relatively small SMT pad location 22. The relatively large SMT pad location 23 can be substantially filled by four shaped deposits 25 arranged adjacently in a 2×2 matrix. In total, using this exemplary process, the workpiece W requires eight shaped deposits 25. Because only one shaped deposit 25 can be formed at a time, this requires that the workpiece W be moved eight times relative to the illuminated area of ​​deposition tape 2 onto which it is deposited and then ready for the next deposition, which equates to an improvement in throughput of the order of six times compared to the previously known process described above. Again, of course, the individual shaped deposits 25 will coalesce and spread across the SMT pad locations 22 and 23 during the subsequent reflow process.

[0022] While the previous examples described the formation of substantially rectangular SMT pads, such methods may likewise be used to create other shaped SMT pads including, by way of example only, circular, triangular, square, arcuate, elliptical, oval, or cross-shaped SMT pads, or combinations thereof, such as so-called "home base" or "inverted home base" pads.

[0023] Figure 4 shows a schematic view from above of a workpiece W undergoing a wafer bumping process, and Figures 5A-5C and 6A-6B depict two different embodiments for performing such a wafer bumping process. As shown in Figure 4, a rectangular workpiece W is shown having an array of 625 ball locations 26, i.e., a 25x25 matrix array, at which bumps or balls of deposition medium are formed.

[0024] In the known wafer bumping process, using a known LAD apparatus 1 shown in Figure 1, individual paste droplets are deposited by irradiating an irradiated area of ​​the deposition tape 2 with an unshaped beam 8 such that a single deposition medium droplet is extruded from the deposition tape 2 onto the ball locations 26. Thus, using this known process, 625 times the workpiece W must be deposited onto and then moved relative to the deposition tape 2 ready for the next deposition. Following such deposition, the workpiece W is subjected to a reflow process to form bumps or balls at each ball location 26.

[0025] In the next two embodiments, a LAD apparatus 20 is used in which a beam splitter 21, e.g. an SLM or DOE, acts to split the laser beam 8 into a number of spatially separated sub-beams, in these examples 25 sub-beams. For example, if the laser source 7 has a power of 25 W, each sub-beam may have a power of 1 W, which is sufficient to push a droplet of deposition material from the deposition tape 2.

[0026] 5A-5C show the workpiece W of FIG. 4 from above, diagrammatically, during a stage of a wafer bumping process according to an embodiment of the present invention, in which 25 sub-beams are arranged adjacent to each other in a 5×5 matrix. As shown in FIG. 5A, in a first step, the workpiece W is moved relative to the irradiation area of ​​the deposition tape 2 so that the matrix of sub-beams coincides with 25 ball positions in the upper left area of ​​the workpiece W as shown. The filled ball positions 26 in this position are shown in black as 27. Following deposition, as shown in FIG. 5B, the workpiece W is moved relative to the irradiation area of ​​the deposition tape 2 so that a contiguous set of 25 ball positions 26 coincides with the sub-beams. Once these ball positions 26 are filled, the workpiece W is again moved relative to the irradiation area to enter the position shown in FIG. 5C, in which the 25 ball positions 26 are again filled. The process can be repeated, for example in a rastering manner, until all ball locations 26 are filled with their respective deposition medium drops. With this exemplary process, the workpiece W must be deposited on and then moved relative to the deposition tape 2 ready for the next deposition only 25 times, achieving a 25-fold improvement in throughput compared to the previously described known process. The workpiece is then subjected to a reflow process to form bumps or balls in each filled ball location 26.

[0027] 6A, 6B show the workpiece of FIG. 4 from above, diagrammatically, during a stage of a wafer bumping process according to another embodiment of the invention. This is similar to the embodiment described above with reference to FIGS. 5A-5C, except that in this case the sub-beams comprise a certain array of sub-beams, the sub-beams having a pitch that is a multiple of the pitch of the ball array. As shown, the pitch of the sub-beam array is three times the pitch of the ball array. As in the previously described embodiment, 25 ball positions 26 are filled with a single "shot", followed by a relative movement of the workpiece W and the irradiated area, and the filling of the next 25 ball positions 26. This embodiment is advantageous in that the laser power is spread more widely over a correspondingly larger irradiated area of ​​the deposition tape 2, thereby reducing localized heating of the deposition tape 2, and therefore possible distortion.

[0028] The above-mentioned embodiments are merely examples, and other possibilities and alternatives within the scope of the present invention will be apparent to those skilled in the art. For example, the LAD apparatus may be provided with two or more beam shapers, each of which is selectively movable into the optical path of the laser beam emitted from the laser source. Each beam shaper may be configured to shape the laser beam into a specific irradiation pattern as required by the application. This may be particularly advantageous, for example, when SMT pads need to be formed on workpieces having unusual shapes or dimensions.

[0029] Additionally or alternatively, if the laser beam is split by a beam shaper, the shape and size of each sub-beam can be fully customized to suit the application, and they do not necessarily have to have identical portions. [Explanation of symbols]

[0030] 1, 20 Laser assisted deposition (LAD) equipment 2. Deposit Tape 3. Solder Paste 4. Stacked Tape Storage Reels 5 Used tape reels 6, 6A, 6B Rollers 7 Laser Source 8 Laser Beam 8´ Shaped laser beam 9. Coating Tape 10 Coating tape storage reel 11 Used reels of coating tape 12 Pasting Area 13, 14 Laura 15 Paste distributor 16 Platform 21 Beam shaper, beam splitter 22 (relatively) small SMT pad locations 23 (relatively) large SMT pad locations 24 Spot deposits 25 Molded deposit 26 Ball Position 27 Ball receiving deposition W Workpiece

Claims

1. 1. A laser-assisted deposition apparatus for depositing a deposition medium from a tape onto a workpiece to form features on the workpiece, the tape having upper and lower major surfaces, the lower major surface being coated with the deposition medium, the laser-assisted deposition apparatus comprising: a tape advancement mechanism for moving the tape through the laser assisted deposition apparatus along a movement path; a laser source operable to direct a laser beam along an optical path toward the top major surface of the tape at an illumination area thereof; a workpiece support for supporting the workpiece proximate the lower major surface such that, when the laser beam is directed toward the illumination area, the deposition medium disposed on the lower major surface and coincident with the illumination area can be ejected from the lower major surface onto the workpiece; a beam shaper disposed in the optical path to create an illumination pattern in the illumination area; A laser assisted deposition apparatus comprising:

2. 10. The laser assisted deposition apparatus of claim 1, wherein the feature comprises an SMT pad and the illumination pattern has a size and shape that matches the SMT pad.

3. 3. The laser-assisted deposition apparatus of claim 2, wherein the laser-assisted deposition apparatus is operable to form a plurality of SMT pads on the workpiece, and the illumination pattern corresponds to a smallest SMT pad of the plurality of SMT pads.

4. The laser assisted deposition apparatus of claim 1 , wherein the beam shaper acts to split the laser beam into a plurality of spatially separated sub-beams.

5. The laser assisted deposition apparatus of claim 1 , wherein the beam shaper comprises a diffractive optical element.

6. The laser assisted deposition apparatus of claim 1 , wherein the beam shaper comprises a spatial light modulator.

7. 1. A method for forming features on a workpiece by depositing a deposition medium from a tape onto the workpiece, comprising the steps of: i) providing the tape having an upper major surface and a lower major surface, the lower major surface being coated with the deposition medium; ii) providing a laser assisted deposition apparatus having a laser source; iii) supporting the workpiece adjacent the lower major surface; iv) advancing the tape along a travel path through the laser assisted deposition apparatus; v) directing a laser beam from the laser source along an optical path toward the top major surface of the tape at an illumination area thereof, such that the deposition medium located on the bottom major surface thereof and coincident with the illumination area is emitted from the bottom major surface onto the workpiece; Including, and v) shaping the laser beam to produce an illumination pattern in the illumination area. method.

8. The method of claim 7 , wherein the characteristic includes an SMT pad and the illumination pattern has a size and shape that matches the SMT pad.

9. 9. The method of claim 8, comprising forming a plurality of SMT pads on the workpiece, and wherein the illumination pattern corresponds to a smallest SMT pad of the plurality of SMT pads.

10. 10. The method of claim 9, comprising forming larger SMT pads of the plurality of SMT pads by moving the illumination pattern relative to the workpiece such that larger SMT pads are formed from adjacent deposits of the deposition medium, each of which conforms to the illumination pattern.

11. The method of claim 7 , wherein step v) comprises passing the laser beam through a beam shaper.

12. 1. A method of performing wafer bumping to form bumps or balls of a deposition medium on a workpiece in a regular pitch array, comprising: i) providing a tape having upper and lower major surfaces, said lower major surface being coated with said deposition medium; ii) providing a laser assisted deposition apparatus having a laser source; iii) supporting the workpiece adjacent the lower major surface; iv) advancing the tape along a travel path through the laser assisted deposition apparatus; v) directing a laser beam from the laser source along an optical path towards a beam shaper, the beam shaper splitting the laser beam into a plurality of spatially separated sub-beams; vi) directing the plurality of spatially separated sub-beams onto the top major surface of the tape to form an illumination pattern in the illumination area, the deposition medium being projected from the bottom major surface onto the workpiece, the deposition medium being disposed on the bottom major surface and coincident with the illumination pattern; A method comprising:

13. The method of claim 12 , wherein the plurality of sub-beams comprises an array of sub-beams, the array of sub-beams having a pitch that is a multiple of the pitch of the array.

14. The method of claim 12 , wherein the beam shaper comprises a diffractive optical element.

15. The method of claim 12 , wherein the beam shaper comprises a spatial light modulator.

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