Patent Application
20120171372
1. Technical Field
This disclosure is related generally to the field of adhesive dispensing systems, and in particular to systems for dispensing adhesives in automated assembly systems where the position and volume of the dispensing are critical, including systems for assembly and packaging of semiconductor based devices, and electronic devices in general.
2. Description of the Related Art
A number of different types of adhesives are commonly used in the “back end” processes of semiconductor device manufacture, and in assembly of electronic devices. Examples include thermally conductive adhesives used to mechanically bond semiconductor dice to lead frames and to transmit heat to the lead frames; adhesives used to hermetically seal covers onto microelectromechanical devices formed on semiconductor wafers; adhesives used to attach lenses to semiconductor dice over optical sensors; solvent adhesives used to assemble plastic components; elastomeric adhesives to join components and dampen vibrations between the components, etc. Very often, adhesives must be deposited with great precision to avoid damaging the devices being bonded. In most cases, these adhesives are applied onto one of the surfaces to be bonded by automatic dispensers as part of an automated assembly process. Misplacement of such adhesives can often cause cosmetic or substantive damage to a device that will render the device unsalable.
One example of an automated adhesive dispensing system is shown in
The dispensing system 100 is part of a robotic assembly system for packaging semiconductor devices, and is carried by a first robotic arm 102 of the assembly system. The assembly system also includes a second robotic arm 120 that carries a placing fixture 124 for placing lenses 126, which is shown in
The adhesive dispenser 104 comprises a dispenser body 105 and a nozzle 107 that includes a needle tip 106. The dispenser 104 is configured, in the example shown, to deposit adhesive onto semiconductor dice 110 in which optical sensors 112 have been formed. The fiducial camera 116 is configured to detect fiducial marks on each die 110. The dice 110 are mounted in quantities of about 50-100 on a carrier 114, sometimes referred to as a stiffener, having a size of about 400-1000 cm2. The carrier 114 is moved though various stages of the assembly process by a transport system, which is not shown.
The second robotic arm 120 carries a second support fixture 122 to which a component placement device 124 is coupled for placing the lenses 126.
In the stage depicted in
It is important that the deposition of the adhesive be precisely controlled both in terms of volume and location. When the lens 126 is placed over the adhesive, capillary action of the fluid adhesive between the lens and the surface of the semiconductor die 110 draws the lens into close contact with the die, with only a thin film of adhesive between the lens and the die. If too much adhesive is deposited, it will flow onto the surface of the optical sensor, which will ruin the device, while too little adhesive will not properly bond the lens to the die. If the adhesive is not positioned correctly, it will either fail to contact the lens along one or more edges, or will again flow onto the sensor.
Additionally, the adhesive is preferably very thin, having a viscosity approaching that of water. If the adhesive is too viscous, it can fail to flow properly when the lens is positioned, leaving an uneven surface, so that the lens is out of plane. Furthermore, adhesive viscosity controls the thickness of the film between the lens and the surface of the die, which in turn controls the distance of the lens from the sensor. Thus, if the adhesive is too viscous, the lens will be seated farther from the sensor, and the focal length will be adversely affected.
In order to adequately control the adhesive deposition, the needle tip 106 of the adhesive dispenser 104 is very fine, having a bore, typically, of around 150-250 μm. Dispensers typically employ one of two types of mechanisms to meter the adhesive. One class of dispensers employ mechanical control, such as by a screw-driven plunger, in which movement of a plunger in the body of the dispenser forces fluid out the tip 106. Rotation of a drive screw advances the plunger within a syringe to force fluid from the needle tip. Control of fluid volume can be very precise because each rotation or fractional rotation of the screw moves the plunger a known distance, displacing a calculable volume within the syringe, and forcing an equal volume of fluid adhesive from the nozzle.
The other class of dispensers uses pneumatic pressure behind the adhesive in the dispenser to force fluid through the tip 106. Pneumatic dispensers are not as inherently precise as screw-driven dispensers because gas is compressible, so that for a given volume of gas moved into the dispenser it is not inherent that an equal volume of adhesive will be dispensed. Nevertheless, pneumatic dispensers can be precisely controlled, provided factors such as the viscosity and rheology of the adhesive, and the bore and length of the needle tip, are accounted for. Pneumatic dispensers are usually less expensive, and maintenance is easier and faster. However, in general, mechanically controlled dispensers are preferred for very low viscosity adhesives, because fluid flow can be closely and directly controlled, making it easier to maintain the flow of adhesive through the nozzle to within tolerances.
In automated adhesive systems for semiconductor device manufacture, an automatic shutter system is provided for use with an adhesive dispenser system that is configured to deposit adhesive for joining elements during final assembly processes. According to an embodiment, an arm is coupled to the adhesive dispenser system so as to be movable relative to the adhesive dispenser. The arm carries a shutter that it moves between a closed position, in which the shutter is interposed between a nozzle of the adhesive dispenser and a working surface, and an open position, in which the shutter is not interposed between the nozzle and the working surface.
Operation of the arm and shutter is controlled so that the shutter is moved to the closed position while the dispenser is in a ready position and not actually delivering adhesive, and to the open position as, or immediately before the needle tip descends to a dispensing position to deposit adhesive on a device. In this way, drops of adhesive that fall from the needle tip while in the ready position are captured by the shutter and prevented from falling onto a device in process in an unintended location of the device.
A number of different structures of the shutter system are shown and described, according to respective embodiments.
With regard to the screw-driven adhesive dispensing systems referred to in the background, the inventors have found that there are problems associated with such systems that can interfere with their efficient operation. In the dispenser of these systems, the screw-driven plunger is powered by an electric motor. In high-speed production environments, the motor operates at an increased duty cycle, generating increased heat, which warms the adhesive in the dispenser. While the adhesive is typically a two-part adhesive that cures by catalysis, heat accelerates this process. Thus, the adhesive can begin to cure while still in the dispenser. This results in a more viscous adhesive, which can affect the final product, as discussed with reference to example described in the background. Additionally, the more viscous adhesive requires greater force to dispense through the very small needle tip, which increases the load on the motor, requiring more power, and generating more heat, while restricting fluid flow. Ultimately, in the worst case, the needle tip can become completely blocked, so that no adhesive is dispensed. When this occurs, the system can continue in operation without depositing adhesive, so that the lenses are placed on a dry surface. In some cases, such a condition can continue for some time before being discovered, resulting in a significant amount of rework or ruined product.
One solution is to use a pneumatically pressurized dispenser, which eliminates the heating problem. While such dispensers require care in controlling fluid flow during operation, the inventors believe that it is a generally viable solution. Unfortunately, the inventors have encountered another problem that can occur, most frequently in association with pneumatically pressurized systems, although mechanically pressurized systems are not immune.
As noted above, to achieve precise positioning of adhesives, many adhesive dispensing systems use optical pattern recognition systems that scan the surface of each die to locate fiducials to ensure that the deposit of adhesive is correctly positioned and oriented. As the camera moves back and forth over the dice on the carrier to determine the position and orientation of each of the sensors, a drop of adhesive can drip from the needle tip of the dispenser. If it lands on one of the sensors, it will ruin that device, because, even if it were discovered immediately, it could not be wiped away without damage to the sensor. Furthermore, such drops are generally miniscule, and nearly impossible to detect by visual inspection, so they are usually not discovered until after the devices go through several additional packaging and assembly steps, when the sensors are tested. In functional tests, a drop appears to be a group of dead cells, producing a black spot on an image, resulting in rejection of the entire part, both the lens and the die. Thus, not only are the semiconductor device and lens discarded, but the additional time and materials thereafter expended to move that device toward completion were also wasted. Nevertheless, the expense of losses due to adhesive drips, which are relatively rare, is significantly less than losses arising from premature curing of adhesive caused by parasitic heat. To the extent that damage caused by adhesive drips may have been previously recognized as a problem, it appears that manufacturers have been willing to accept them as an additional production cost. However, most manufacturers continue to employ screw-driven systems for applications that require low-viscosity adhesives and a high degree of control over volume and placement.
The inventors believe that damage caused by adhesive drips can be substantially reduced or eliminated using a simple and inexpensive mechanism, various embodiments of which are described below.
In addition to elements previously described, the dispenser system 200 includes a shutter system 210 that is configured to interpose a shutter 212 between the needle tip 106 and the working surface below except while the dispenser 104 is in the process of dispensing adhesive. The shutter system 210 comprises a pivot arm 214 that is rotatably coupled to a first support bracket 218 at a pivot point 216, the support bracket serving to couple the pivot arm to the support fixture 103. A bumper 220 is coupled to a first end of the pivot arm 214, and bears against an upper surface of the dispenser body 105 while the dispenser 104 is in the ready position, as shown in
While the dispenser 104 is in the ready position, as shown in
In dispenser systems that are used in high-speed production, movement of the dispenser body 105 from the ready position to the dispensing position can be extremely fast, and in some cases, might exceed the speed at which the pivot arm 214 can rotate the shutter 212 out of the path of the descending needle tip 106. Responsiveness of the pivot arm 214 can be modified by adjusting the balance of the arm. If additional weight is added to the pivot arm 214 at or near the bumper 222, the arm will more quickly rotate away from the closed position, as the added weight more quickly overcomes static friction at the pivot point, and the vector of force acting to rotate the arm becomes more vertical. However, if the dispenser moves at speeds that approach or exceed the acceleration of gravity, it can become impossible for a gravity-operated pivot arm to move with sufficient speed. In such cases, one or more springs can be employed to reduce response time. For example, a torsion spring positioned at the pivot point 216 and configured to bias the pivot arm toward the open position will increase the speed of response of the pivot arm 214.
In a dispenser system like the one described with reference to
It can be seen, with reference to
In prototype tests with a conventional dispenser system, the inventors installed a shutter system that operates substantially as described with reference to the embodiment of
Turning now to
While the dispenser 104 is in the ready position, the screw arm 242 and shutter 212 are in the closed position, as shown in
As with the embodiment described with reference to
While the dispenser system 290 is in the ready position, the swing arm 302 hangs from the pivot pin 306 and supports the shutter 212 in the closed position, as shown in
As with previously described embodiments, the embodiment of
The shutter system 270 includes a screw arm 272 to which the shutter 212 is coupled, the screw arm 272 also includes long-lead threads 248 extending along a portion of its length, and splines 273 extending along a portion of the screw arm at a first end thereof. A first support bracket 274 is coupled to the support fixture 130 and to the first end of the screw arm 272. A motor 276 is coupled to the support fixture 130, and rotationally coupled to the screw arm 262, as will be described in more detail below with reference to
Rotation of the motor 276 is transmitted by the motor shaft 286 and drive gear 288 to the splined gear 282 and thence to the screw arm 272. Rotation of the screw arm 272 applies an axial force to the sliding nut 280, which causes relative axial movement between the screw arm and the sliding nut. Because the first and second support brackets 274, 278 are both rigidly fixed to the support fixture 130, the sliding nut 280, supported by the second support bracket, cannot move relative to the splined gear 274, which is supported by the first support bracket. Thus, when the screw arm 272 rotates, the screw arm itself is compelled to move axially. The splined engagement of the screw arm 272 and the splined gear 282 permits the screw arm to slide within the splined gear while remaining rotationally coupled thereto.
The dispensing system 260 is configured to signal the motor 276 as it initiates movement from the ready position to the dispensing position. The motor 276 is controlled to rotate a preselected number of rotations, which are transmitted to the screw arm 272. Rotation of the screw arm 272 rotates the shutter 212 from the closed position to the open position, and at the same time lifts the screw arm relative to the dispenser 232 and support fixture 130 because of the axial force applied to the sliding nut 280. This raises the shutter 212 a distance that is sufficient to prevent the shutter from striking the working surface as the dispensing system 260 drops to the dispensing position. When the dispensing system 260 returns to the ready position, another signal is sent to the motor 276, which is controlled to rotate in the reverse direction the same number of rotations, to return the screw arm 272 and shutter 212 to the closed position. Various methods for electronic control and timing of the embodiments of
The shutter system 310 includes a first translating arm 314 and a second translating arm 316 to which the shutter 212 is coupled. The first translating arm 314 is slidingly coupled to the support fixture 1 via a first support bracket 318 which also houses a first solenoid 320. The second translating arm 316 is slidingly coupled to the first translating arm 314 via a second support bracket 322 which also houses a second solenoid 324. First and second stops 326, 328 are coupled to the first translating arm 314, and third and fourth stops 330, 332 are coupled to the second translating arm 316. A first extension spring 334 is coupled to the first translating arm 314 between the second stop 328 and the first support bracket 318, and a second extension spring 336 is coupled to the second translating arm 316 between the fourth stop 332 and the second support bracket 322.
The first and third stops 326, 330 limit extension of the first and second translating arms 314, 316, respectively, and the second and fourth stops 328, 332 limit retraction of the first and second translating arms, respectively. The first and second extension springs 334, 336 bias the first and second translating arms 314, 316, toward full extension, as indicated by arrows E1 and E2. When energized, the first solenoid 320 applies to the first translating arm 314 a retraction bias, indicated by arrow R1 in
While the dispenser 132 is in the ready position, the first and second solenoids 320, 324 are not energized, so that the first and second translating arms 314, 316 are maintained in their respective extended positions by the biasing forces of the first and second extension springs 334, 336, and the shutter 212 is maintained in the closed position, as shown in
Retraction and extension of the first translating arm 314 moves the second translating arm 316 and the shutter 212 in the Z axis, while retraction and extension of the second translating arm moves the shutter in the X axis. According to an embodiment, when moving the shutter 212 from the closed to the open positions, the second translating arm 316 is retracted earlier than the first translating arm 314 so that the shutter 212 is moved laterally beyond the end of the needle tip 106 before the first translating arm lifts the second translating arm and shutter. In contrast, when moving the shutter 212 from the closed to the open positions, the first translating arm 314 is extended before the second translating arm 316 so that the shutter 212 is below the end of the needle tip 106 before the second translating arm extends the shutter toward the closed position.
Provision of timing of, and power for energizing of the first and second solenoids is well within the abilities of one of ordinary skill in the art. Integration of the shutter system 302 with the operation of the dispenser system 300 can be accomplished in a number of different ways, including by methods similar to those discussed with reference to the embodiment of
According to another embodiment, a shutter system is similar in many respects to that described with reference to
Turning now to
While the dispenser 132 is in the ready position, the translating arm 344 is maintained in its extended position with the shutter 212 in the closed position, as shown in
When the dispenser 132 begins to return to the ready position from the dispensing position, the motor 348 rotates in a second rotation direction, opposite the first rotation direction, extending the translating arm 344 by operation of the rack-and-pinion mechanism 350, as indicated by the arrow E3 In
Control of operation of the shutter systems 270, 310, and 340, described above with reference to
It will be recognized that the simple arrangement described above can be adapted to control the motor 348 of the embodiment of
With regard to the embodiment of
According to other embodiments, the pressure switch is replaced with a sensor, such as, e.g., a proximity or hall-effects sensor, to function as the fixture position detector.
The dispenser system will typically be controlled, perhaps along with other elements of the associated assembly system, by software instructions that are executed by a microprocessor. The microprocessor may be a dedicated processor that is integral to a component of the assembly system, or it may be a general purpose processor that is part of a stand-alone computer system that is coupled to the assembly system. In either case, an instruction to switch from the ready position to the dispensing position will include a change in a logic value at one or more terminals in a control circuit of the dispenser system. According to an embodiment, the input of the dedicated logic circuit is coupled to an appropriate terminal of the control circuit in order to detect the change in a logic value, which replaces the fixture position detector as a means for signaling a change from the ready position to the dispensing position and vice-versa.
Finally, according to an embodiment, the software instructions that control operation of the dispenser system include instructions to provide a first logic value at an input terminal of the dedicated logic circuit to command a change of the shutter system from the closed to the open position, and to provide a second logic value to command a change from the open to the closed position.
In describing the operation of the shutter systems described with reference to
The shutter systems of
While the invention has been described and illustrated primarily with reference to systems for applying adhesive to optical sensors on semiconductor dice, the principles of the invention can be applied with advantage to any system that is employed to automatically dispense adhesive, especially where drops of the adhesive in unintended locations can damage products in process. Accordingly, except where a particular system is explicitly claimed, the claims are not limited in that respect. The term working surface is used to refer broadly to any surface or structure positioned under the nozzle of an adhesive dispenser, particularly in a position where it can receive an adhesive.
Because the drawings are diagrammatic, they are not intended to show details of actual dispensing systems, except where those details are specifically referred to and described. Otherwise, the drawings are intended to convey the function of the elements depicted. In particular, elements of known systems, such as robotic arms, support fixtures, cameras, adhesive dispensers, etc., are well known in the art, and can have any of a large number of shapes and structures, which vary widely according to system, manufacturer, capacity, model, etc. Even the structures that are described in detail are provided as examples of various structures that can be employed, according to the preferences of a user or the limitations imposed by a particular dispensing system.
Most of the drawings are presented as side views of respective dispensing systems, and drawings that show views from other vantage points are defined accordingly. This is used to provide a common point of reference for the drawings, and does not impose any limitations. Furthermore, claim limitations that read on elements that are shown in the drawing as being, for example, positioned in front of an adhesive dispenser, or at the side, are not limited to the position shown.
The unit symbol “μm” is used herein to refer to a value in microns. One micron is equal to 1×10−6 meters.
Ordinal numbers, e.g., first, second, third, etc., are used according to conventional claim practice, i.e., for the purpose of clearly distinguishing between claimed elements or features thereof. The use of such numbers does not suggest any other relationship, e.g., order of operation or relative position of such elements, nor does it exclude the possible combination of the listed elements into a single, multiple-function, structure or housing. Furthermore, ordinal numbers used in the claims have no specific correspondence to those used in the specification to refer to elements of disclosed embodiments on which those claims read.
Where a claim limitation recites a structure as an object of the limitation, that structure itself is not an element of the claim, but is a modifier of the subject. For example, in a limitation that recites “a shutter system configured to be coupled to an adhesive dispenser system,” the adhesive dispenser system is not an element of the claim, but instead serves to define the scope of the subject term shutter system. Additionally, subsequent limitations or claims that recite or characterize additional elements relative to the adhesive dispenser system do not render the adhesive dispenser system an element of the claim.
The term coupled, as used in the claims, includes within its scope indirect coupling, such as when two elements are coupled with one or more intervening elements even where no intervening elements are recited.
The abstract of the present disclosure is provided as a brief outline of some of the principles of the invention according to one embodiment, and is not intended as a complete or definitive description of any embodiment thereof, nor should it be relied upon to define terms used in the specification or claims. The abstract does not limit the scope of the claims.
Elements of the various embodiments described above can be combined, and further modifications can be made, to provide further embodiments without deviating from the spirit and scope of the invention. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
