BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1D illustrate a prior art semiconductor packaging system for attaching a die to a lead frame.
FIG. 2A is a perspective view of an example shower head dispenser constructed in accordance with the teachings of the invention.
FIG. 2B is an exploded view of the example shower head dispenser of FIG. 2A.
FIG. 2C is an enlarged plan view of the dispensing tip of the example shower head dispenser of FIGS. 2A and 2B.
FIG. 3 is a cross-sectional view of the example shower head dispenser of FIGS. 2A-2C.
FIGS. 4A-4E are a series of cross-sectional views similar to FIG. 3 illustrating the shower head dispenser dispensing adhesive on an example lead frame.
FIG. 5 is a top view of an example pattern of deposited adhesive formed by the example process shown in FIGS. 4A-4E using the example shower head dispenser of FIGS. 2A-2C and 3.
FIG. 6 is a plan view of the tip of another example shower head dispenser.
FIG. 7 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 6.
FIG. 8 is a plan view of the tip of another example shower head dispenser.
FIG. 9 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 8.
FIG. 10 is a plan view of the tip of another example shower head dispenser.
FIG. 11 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 10.
FIG. 12 is a plan view of the tip of another example shower head dispenser.
FIG. 13 is a plan view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 12.
DETAILED DESCRIPTION
It has recently become desirable to employ epoxies having improved thermal conductivity characteristics to bond a die to a lead frame. For example, the epoxy sold under the trade name QMIJ2951, the epoxy sold under the trade name QMI-529HT and other conductive or non-conductive epoxy pastes are advantageous in bonding dies to lead frames because they improve the thermal conductivity of the resulting package. However, these epoxies exhibit high viscosity (e.g., 5 rpm), and, thus, when distributed through a prior art shower head dispenser such as that shown in FIGS. 1A and 1B above, these epoxies exhibit undesirable tailing which may result in voids in the epoxy bond. To avoid the tailing issue, these epoxies may be effectively dispensed through prior art pen dispensers, but this achievement comes at the expense of units per hour production rates.
An example shower head dispenser 40 constructed in accordance with the teachings of the invention is shown in FIGS. 2A-2C. The shower head dispenser 40 of the illustrated example can be mounted on the adhesive magazine of an adhesive dispenser such as the example adhesive magazine 9 of the example adhesive dispenser 3 of FIG. 1A via a locking collar 13 or the like to dispense high viscosity adhesives such as the QMIJ2951 epoxy, the QMI-529HT epoxy or the other conductive or non-conductive epoxy pastes mentioned above without suffering from the tailing and accompanying void problems of prior art shower head dispensers. Thus, the example shower head dispenser 40 illustrated in FIGS. 2A-2C advantageously achieves higher units per hour throughput relative to prior art pen dispensers, without suffering the tailing, voiding or adhesive waste problems of prior art shower head dispensers.
Before describing the example shower head dispenser 40 in further detail, it should be noted that while reference will be made to using a relatively high viscosity die attach material, such as the epoxies sold under the trade names QMIJ2951 or QMI-529HT, with the example shower head dispenser 40, other epoxies and other adhesives, such as polyimide-based and/or silicone-based materials, could likewise be employed.
FIG. 2A is a perspective view of an example shower head dispenser 40. As shown in FIG. 2A, the example shower head dispenser 40 includes a body 42 for securing the example shower head dispenser 40 to an adhesive magazine and a shower head tip 44 for dispensing a pattern of adhesive on a lead frame (e.g., lead frame 2 of FIGS. 1A-1D) or the like. The body 42 defines a bore 43 for receiving adhesive material from the adhesive magazine. The example shower head tip 44 includes a rectangular projection 46 defining a lumen 48 to transport adhesive from the body 42 to a material dispensing cavity 50. In the illustrated example, the dispensing cavity 50 has a star shape to facilitate dispensing adhesive on a lead frame in a star shaped pattern. The example body 42 and the example shower head tip 44 are threadingly secured to one another to facilitate cleaning or repair (See FIG. 2B). A valve or seal is disposed between the adhesive magazine and the dispensing cavity 50 to ensure adhesive is dispensed into the shower head dispenser 40 in a controlled fashion.
FIG. 2C is an enlarged plan view of the example shower head tip 44 of the example shower head dispenser 40 of FIGS. 2A and 2B. FIG. 3 is a cross-section view of the example shower head tip 44 taken along line 3-3 in FIG. 2C. As stated above, the projection 46 of the shower head tip 44 defines a lumen 48 to transport adhesive to an adhesive dispensing cavity 50. The lumen 48 is defined by the side walls 52 and bottom plate 56 of the shower head tip 44. The lumen 48 can have similar dimensions as the star-shaped cavity 50 for its entire length (e.g., the lumen 48 may be a star-shaped channel corresponding to the size and shape of the star-shaped cavity 50 or a rectangular channel with a diameter almost as large as the projection 46), or the lumen 48 can be smaller than the star-shaped cavity 50 for most of its length (e.g., the lumen 48 can be structured as a cylinder with a diameter much smaller than the diameter of the projection 46), but widened or flared at the tip of the lumen 48 to deliver adhesive across the entire star-shaped cavity 50.
As shown in FIG. 2C, in the illustrated example, the bottom plate 56 has a bottom surface 62 defining the star-shaped dispensing cavity 50. As explained further below, the star-shaped dispensing cavity 50 is dimensioned to ensure that an amount of adhesive sufficient to cover a bonding area between a die 6 and a lead frame 2 is quickly dispensed (e.g., in a single shot) to achieve a desired bond line thickness, while avoiding tailing and die tilt issues that could result in unsatisfactory bonding. Although the illustrated example employs a star shaped dispensing cavity 50, persons of ordinary skill in the art will understand that other patterns may be used.
The star-shaped dispensing cavity 50 of the illustrated example has four lateral arms 74, 76, 78 and 80. Each of the lateral arms 74, 76, 78 and 80 includes a number of holes 82 which are bored through the bottom plate 56 to provide communication between the dispensing cavity 50 and the lumen 48. Each of the lateral arms 74, 76, 78 and 80 of the star-shaped cavity 50 is defined by a pair of opposed raised side walls 84 and 96 and a raised corner wall 104. The side walls 84, 96 and the end walls 104 cooperate to form a closed loop raised wall projecting from the bottom plate 56. The raised wall cooperates with the bottom plate 56 to define the star-shaped dispensing cavity 50. The side of the star-shaped cavity 50 opposite the bottom plate 56 is open and can be positioned adjacent a lead frame (e.g., such as lead frame 2 of FIG. 1B) to transfer adhesive from the cavity 50 to the lead frame 2. In the illustrated example, the side walls 84, 96 and the end walls 104 cooperate to form a substantially continuous contact surface 132 to engage a lead frame (e.g., such as lead frame 2 of FIG. 1B).
To reduce tailing of adhesive when the example shower head dispenser 40 is lifted from the lead frame after dispensing adhesive, in the illustrated example the contact surface 132 formed by the side walls 84, 96 and the end walls 104 defining the star-shaped cavity 50 is coated with a layer of non-stick material 134. In the illustrated example, the non-stick material 134 is polytetrafluoroethylene (PTFE), which is commonly referred to as Teflon. This Teflon coating reduces surface tension between the adhesive pattern and the shower head dispenser 40, thereby reducing the tendency for the adhesive to lift up (i.e., tail) with the lifting shower head dispenser 40. Teflon is advantageous in this role because it is stable under a wide range of temperatures, it is chemical resistant and it exhibits low conductivity.
The volume of the star-shaped dispensing cavity 50 of the illustrated example is selected to correspond to the amount of adhesive desired to be placed on a lead frame for a die surface of interest and is, thus, application dependent. In the example illustrated in FIGS. 2A-2C and 3, the combined height of the opposed side walls 84, 96 and Teflon coating 134 relative to most of the bottom plate 56 is approximately two micro inches. However, to increase the amount of adhesive dispensed at the corners of the star-shaped dispensing cavity 50, the bottom plate 56 is recessed at each of the corners of the star-shaped cavity 50 such that the height of the Teflon coated end walls 104 relative to the bottom plate 56 is approximately three micro inches. As shown in FIG. 2C, this height difference is achieved in the illustrated example by a circular recess 100 formed at each corner of the star-shaped cavity 50. Die tilt is improved by this approach because the recesses 100 ensure that the height of the adhesive dispensed at the corners of the star shaped adhesive pattern is substantially similar to the height of the adhesive dispensed at the center of the star-shaped adhesive pattern when a die is pressed against the adhesive. In other words, the adhesive pattern dispensed using the example shower head dispenser 40 has a generally uniform height when compressed by a die.
The channel pitch of the holes 82 (i.e., the distance between the centers of two immediately adjacent holes 82) is selected to ensure substantially uniform and complete filling of the star-shaped cavity 50 with adhesive material in a short time period during the adhesive application process. Selecting the locations and pitch of the holes 82 is an empirical process based on factors such as the properties (e.g., viscosity) of the adhesive to be employed, the die size, the permissible fillet size (i.e., the height of the adhesive bond viewed from the side of the die), the area to be covered on the lead frame and the desired dispensing time. For example, it is common to require the adhesive to cover 95% of the area under the die, and for the fillet to be on the order of 0.1 mm or less. To meet these criteria using the QMI-529HT epoxy adhesive mentioned above, in the example illustrated in FIGS. 2A-2C and 3, the channels formed by the opposed side walls 84, 96 are approximately 0.7 mm in width, each of the holes has a diameter of approximately 0.2 mm, the holes are substantially evenly spaced, and the hole pitch is approximately 0.36 mm.
FIGS. 4A-4E illustrate an example process of using the example shower head dispenser 40 of FIGS. 2A-2C and 3 to dispense adhesive on a lead frame such as the lead frame 2 of FIG. 1A. In FIG. 4A, the example shower head dispenser 40 has been aligned with the lead frame (e.g., in the x-y plane of the lead frame) to ensure that the adhesive material is applied in the proper area (e.g., within the area of the die to be bonded to the lead frame). In the example of FIG. 4A, the example shower head dispenser 40 is spaced away from and out of contact with the lead frame, but is being lowered toward the lead frame. In FIG. 4B, the example shower head dispenser 40 has been lowered into contact with the upper surface of the lead frame. In particular, the PTFE layer 134 is in contact with the lead frame to form an enclosed star-shaped volume with the star-shaped dispensing cavity 50.
In FIG. 4C, a controller has been activated to force adhesive through the projection 46 of the example shower head dispenser 40, out of the holes 82 and into the star-shaped cavity 50. An amount of adhesive sufficient to fill or substantially fill the star-shaped cavity 50 is injected through the holes 82, thereby locating a star shaped pattern of adhesive on the surface of the lead frame. The amount of adhesive dispensed may be controlled by, for example, controlling the amount of movement of the piston 11 of FIG. 1A relative to the adhesive magazine 9. The controller is set to dispense an amount of adhesive appropriate for the application at issue.
After the adhesive is dispensed, the shower head dispenser 40 is quickly raised from the lead frame as shown in FIGS. 4D and 4E to produce a star-shaped adhesive pattern on the lead frame. In the illustrated example, the PTFE layer 134 provides a low friction coefficient between the contact surface 132 and the dispensed adhesive to reduce of prevent tailing of the adhesive (i.e., relative to a shower head without the PTFE layer) as the shower head dispenser 40 is raised.
FIG. 5 is a top view of an example star-shaped adhesive pattern 200 deposited by the example shower head dispenser 40 using the example process shown in FIGS. 4A-4E. In the illustrated example, the star-shaped pattern 200 permits the adhesive material to bleed out toward the edges of a die area 202 in a substantially uniform manner without bleeding over the edges of the die area 202. The reduced tailing due to the PTFE layer 134 reduces or eliminates the creation of voids in the adhesive material pattern 200. Because of the recessed corners 100 of the star-shaped cavity 50, the adhesive has a relatively greater height at the corners of the pattern than it would have in the absence of the recesses 100 (see the arrows in the lower right corner of FIG. 3). As a result, the adhesive is more evenly distributed than in adhesive patterns generated via star-shaped shower heads without the PTFE layer. This more even distribution reduces or eliminates the occurrence of die tilt during high speed die bonding.
FIG. 6 is a plan view of the tip of another example shower head dispenser 340. The example shower head dispenser 340 is substantially similar to the shower head dispenser 40, but has different dimensions for a different application. In particular, the example shower head dispenser 340 of FIG. 6 is adapted for distributing QMI-529HT epoxy adhesive on dies ranging from 154-169 mils in the X-direction and 165-181 mils in the Y-direction. In the example of FIG. 6, the channels formed by the opposed side walls 384, 396 are approximately 0.5 mm in width, each of the holes has a diameter of approximately 0.2 mm, the holes are substantially evenly spaced, and the hole pitch is approximately 0.52 mm. FIG. 7 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 6.
FIG. 8 is a plan view of the tip of another example shower head dispenser 440. The example shower head dispenser 440 is substantially similar to the shower head dispenser 40, but has different dimensions for a different application. In particular, the example shower head dispenser 440 of FIG. 8 is adapted for distributing QMI-529HT epoxy adhesive on dies ranging from 189-205 mils in the X-direction and 126-142 mils in the Y-direction. In the example of FIG. 8, the channels formed by the opposed side walls 484, 496 are approximately 0.5 mm in width, each of the holes has a diameter of approximately 0.2 mm, the holes are substantially evenly spaced (other than the center hole), and the hole pitch is approximately 0.69 mm. FIG. 9 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 8.
FIG. 10 is a plan view of the tip of another example shower head dispenser 540. The example shower head dispenser 540 is substantially similar to the shower head dispenser 40, but has different dimensions for a different application. In particular, the example shower head dispenser 540 of FIG. 10 is adapted for distributing QMI-529HT epoxy adhesive on dies ranging from 209-224 mils in the X-direction and 201-217 mils in the Y-direction. In the example of FIG. 10, the channels formed by the opposed side walls 584, 596 are approximately 0.5 mm in width, each of the holes has a diameter of approximately 0.2 mm, the holes are substantially evenly spaced, and the hole pitch is approximately 0.36 mm. FIG. 11 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 10.
FIG. 12 is a plan view of the tip of another example shower head dispenser 640. The example shower head dispenser 640 is substantially similar to the shower head dispenser 40, but has different dimensions for a different application. In particular, the example shower head dispenser 640 of FIG. 12 is adapted for distributing QMI-529HT epoxy adhesive on dies ranging from 354-370 mils in the X-direction and 354-370 mils in the Y-direction. In the example of FIG. 12, the channels formed by the opposed side walls 684, 696 are approximately 0.5 mm in width, each of the holes has a diameter of approximately 0.2 mm, the holes are substantially evenly spaced, and the hole pitch is approximately 0.36 mm. FIG. 13 is a top view of an example pattern of deposited adhesive formed by the example shower head dispenser of FIG. 12.
Although certain example methods, apparatus and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.
Patent Application
20080073028
