Patent Application
20050095367
The present invention generally relates to the dispensing of viscous materials and more particularly, to a method of noncontact dispensing of droplets of viscous materials.
In the manufacture of substrates, for example, printed circuit (“PC”) boards, it is frequently necessary to apply small amounts of viscous materials, i.e. those with a viscosity greater than fifty centipoise. Such materials include, by way of example and not by limitation, general purpose adhesives, solder paste, solder flux, solder mask, grease, oil, encapsulants, potting compounds, epoxies, die attach pastes, silicones, RTV and cyanoacrylates.
In the quest for ever increasing miniaturization of circuitry, a fabrication process known as flip chip technology has developed, which has multiple processes that require viscous fluid dispensing. For example, as shown in
Once the underfill operation is complete, it is desirable that enough liquid epoxy be deposited to cover all of the electrical interconnections, so that a fillet 35 is formed along the side edges of the chip 39. A properly formed fillet ensures that enough epoxy has been deposited to provide maximum mechanical strength of the bond between the chip and the PC board. It is critical to the quality of the underfilling process that the exact amount of epoxy is deposited at exactly the right location. Too little epoxy can result in corrosion and excessive thermal stresses. Too much epoxy can flow beyond the underside of the chip and interfere with other semiconductor devices and interconnections. Therefore, there is a need to constantly improve the accuracy of material deposition to create a fillet of a desired size.
The present invention provides methods of noncontact jetting of a viscous material that reduce a wetted area on a substrate. The methods of the present invention make more efficient use of the dispensed material, which permits more efficient use of the substrate or a reduction in size of the substrate. In addition, by reducing wetted areas, the methods of the present invention provide a potential for greater dispenser velocities, which can reduce dispensing cycle times. Hence, the methods of the present invention are especially useful in performing an underfill operation and can potentially reduce production costs as well as product costs.
The methods of viscous material noncontact jetting of the present invention are also especially useful in those applications where dispensing accuracy and precision are critical.
According to the principles of the present invention and in accordance with the described embodiments, the invention provides a method for noncontact dispensing a viscous material onto a surface of a substrate. The method first provides a jetting valve having a nozzle directing the viscous material flow in a jetting direction nonperpendicular to the surface of the substrate. The jetting process consists of causing the jetting valve to propel a flow of the viscous material through the nozzle with a forward momentum in the jetting direction, breaking the flow of the viscous material using the forward momentum to form a droplet of the viscous material, and applying the droplet of the viscous material to the surface of the substrate using the forward momentum of the droplet. The nonperpendicular jetting direction results in the droplet producing a reduced wetted area on the substrate.
In one aspect of the invention, a positioner supporting the jetting valve is operable to move the jetting valve in a first axis of motion; and the device has a sidewall separated from the surface of the substrate by a gap. The method further comprises orienting the jetting direction oblique to the surface of the substrate and intersecting the substrate at a location in or adjacent to the gap. Then the jetting valve is moved in the first axis of motion with respect to the substrate; and while moving the jetting valve, the steps of causing, breaking, and applying are iterated to apply a linear pattern of viscous material on the substrate adjacent the gap.
In a further aspect of the invention, the positioner is operable to move the jetting valve in a second axis of motion; and the device has first and second sidewalls. The method requires orienting the jetting direction oblique to the surface of the substrate and directed generally toward both the surface of the substrate and the sidewall of the device with a projection of the jetting direction on the substrate being oblique to the first and second sidewalls. Next, the jetting valve is moved in the first axis of motion while the steps of causing, breaking and applying are iterated to apply a linear pattern of viscous material on the substrate adjacent the first sidewall of the device. Thereafter, the jetting valve is moved in the second axis of motion with respect to the substrate while iterating the steps of causing, breaking and applying to apply a linear pattern of viscous material on the substrate adjacent the second sidewall of the device.
In a further embodiment of the invention, the viscous material is a conformal coating material and the method first orients the jetting direction nonperpendicular to the surface of the substrate and intersecting the sidewall of the device. Next, the jetting valve is moved in the first axis of motion with respect to the substrate; and while moving the jetting valve the steps of causing, breaking, and applying are iterated to apply a linear pattern of conformal coating material on the sidewall of the device.
These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein.
A computer 18 provides overall system control and may be a programmable logic controller (“PLC”) or other microprocessor based controller, a hardened personal computer or other conventional control devices capable of carrying out the functions described herein as will be understood by those of ordinary skill. A user interfaces with the computer 18 via a keyboard (not shown) and a video monitor 20. The computer 18 is provided with standard RS-232 and SMEMA CIM communications busses 50 which are compatible with most types of other automated equipment utilized in substrate production assembly lines.
A substrate (not shown) onto which dots of a viscous material, for example, an adhesive, epoxy, solder, etc., are to be applied is located directly beneath a droplet generator 12. The substrate can be manually loaded or transported by an automatic conveyor 22. The conveyor 22 is of conventional design and has a width, which can be adjusted to accept PC boards of different dimensions. The conveyor 22 also includes pneumatically operated lift and lock mechanisms. This embodiment further includes a nozzle priming station 24 and a nozzle calibration set-up station 26. A control panel 28 is mounted on the frame 11 just below the level of the conveyor 22 and includes a plurality of push buttons for manual initiation of certain functions during set-up, calibration and viscous material loading.
Referring to
The axes drives 38 include the X, Y positioner 14 (
The droplet generator 12 includes an ON/OFF jetting dispenser 40, which is a non-contact dispenser specifically designed for jetting minute amounts of viscous material. The dispenser 40 has a jetting valve 44 with a piston 41 disposed in a cylinder 43. The piston 41 has a lower rod 45 extending therefrom through a material chamber 47. A distal lower end of the lower rod 45 is biased against a seat 49 by a return spring 46. The piston 41 further has an upper rod 51 extending therefrom with a distal upper end that is disposed adjacent a stop surface on the end of a screw 53 of a micrometer 55. Adjusting the micrometer screw 53 changes the upper limit of the stroke of the piston 41. The dispenser 40 may include a syringe-style supply device 42 that is fluidly connected to a supply of viscous material (not shown) in a known manner. A droplet generator controller 70 provides an output signal to a voltage-to-pressure transducer 72, for example, a pneumatic solenoid connected to a pressurized source of fluid, that, in turn, ports pressurized air to the supply device 42. Thus, the supply device 42 is able to supply pressurized viscous material to the chamber 47.
A jetting operation is initiated by the computer 18 providing a command signal to the droplet generator controller 70, which causes the controller 70 to provide an output pulse to a voltage-to-pressure transducer 76, for example, a pneumatic solenoid connected to a pressurized source of fluid. The pulsed operation of the transducer 76 ports a pulse of pressurized air into the cylinder 43 and produces a rapid lifting of the piston 41. Lifting the piston lower rod 45 from the seat 49 draws viscous material in the chamber 47 to a location between the piston lower rod 45 and the seat 49. At the end of the output pulse, the transducer 76 returns to its original state, thereby releasing the pressurized air in the cylinder 43, and a return spring 46 rapidly lowers the piston lower rod 45 back against the seat 49. In that process a jet of viscous material is rapidly extruded or jetted through an opening or dispensing orifice 59 of a nozzle 48. As schematically shown in exaggerated form in
A motion controller 62 governs the motion of the droplet generator 12 and the camera and light ring assembly 16 connected thereto. The motion controller 62 provides command signals to separate drive circuits for the X, Y and Z axis motors. A conveyor controller 66 is connected to the substrate conveyor 22. The conveyor controller 66 interfaces between the motion controller 62 and the conveyor 22 for controlling the width adjustment and lift and lock mechanisms of the conveyor 22. The conveyor controller 66 also controls the entry of the substrate 36 into the system and the departure therefrom upon completion of the material deposition. In some applications, a substrate heating system 68 and/or a nozzle heating/cooling system 56 are operative in a known manner to heat the substrate and/or nozzle to maintain a desired temperature profile of the viscous material as the substrate is conveyed through the system.
The nozzle setup station 26 is used for calibration purposes to provide a dot size calibration for accurately controlling the weight or size of the dispensed droplets 37 and a dot placement calibration for accurately locating viscous material dots that are dispensed on-the-fly, that is, while the droplet generator 12 is moving relative to the substrate 36. In addition, the nozzle setup station is used to provide a material volume calibration for accurately controlling the velocity of the droplet generator 12 as a function of current material dispensing characteristics, the rate at which the droplets are to be deposited and a desired total volume of viscous material to be dispensed in a pattern of dots. The nozzle setup station 26 includes a stationary work surface 74 and a measuring device 52, for example, a weigh scale that provides a feedback signal to the computer 18 representing the weight of material weighed by the scale 52. Weigh scale 52 is operatively connected to the computer 18, which is capable of comparing the weight of the material with a previously determined specified value, for example, a viscous material weight setpoint value stored in a computer memory 54. Other types of devices may be substituted for the weigh scale 24 and, for example, may include other dot size measurement devices such as vision systems, including cameras, LEDs or phototransistors for measuring the diameter, area and/or volume of the dispensed material. Prior to operation, a nozzle assembly is installed that is often of a known disposable type designed to eliminate air bubbles in the fluid flow path. Such a dispensing system is more fully described in pending provisional application Ser. No. 60/473,1616, entitled “Viscous Material Noncontact Dispensing System”, filed May 23, 2003, which is hereby incorporated by reference in its entirety herein.
In operation, CAD data from a disk or a computer integrated manufacturing (“CIM”) controller are utilized by the computer 18 to command the motion controller 62 to move the droplet generator 12. This ensures that the minute dots of viscous material are accurately placed on the substrate 36 at the desired locations. The computer 18 automatically assigns dot sizes to specific components based on the user specifications or component library. In applications where CAD data is not available, the software utilized by the computer 18 allows for the locations of the dots to be directly programmed. In a known manner, the computer 18 utilizes the X and Y locations, the component types and the component orientations to determine where and how many viscous material dots to deposit onto the upper surface of the substrate 36.
Known jetting dispensers direct the viscous material in a jetting direction that is substantially perpendicular to the substrate 36; however, with one embodiment of the present invention, as shown in
For example, in an underfilling operation shown in
The desired angle of the jetting direction is application dependent. For example, in an underfilling operation, the jetting direction may be at an angle that is in a range of about 10-80 degrees with respect to the upper surface 80 of the substrate 36. In another application, it is desirable to apply a viscous material to a vertical substrate, for example, a vertical sidewall 82 of the chip 39; and in such application, the jetting direction may be at an angle that is in a range of about 80-100 degrees with respect to the chip sidewall 82.
In use, an optimum angle can be determined in a preproduction jetting cycle during which the viscous material is dispensed with the dispenser 40 mounted at different angles, which are changed by manual adjustments. Based on measurements of the wetted area and other qualitative indicators resulting from jetting at different angles, an optimum angle or range of angles can be determined and recorded. Once a desired jetting angle is determined, during a production cycle, the computer 18 provides output signals to the motion controller 26 causing the motion controller to initiate motion of the dispenser 40 along a first axis of motion, for example, a Y axis of motion as shown in
In addition to rotatably mounting the jetting dispenser 40 at an angle, other structures can be used to provide an angular jetting direction that is nonperpendicular with the substrate surface 80. For example, in another embodiment shown in
In many applications, it is desirable to apply the viscous material along two mutually perpendicular sides of a component. With the angular jetting described with respect to
In a still further embodiment, referring to
In the described embodiments, the angular motions are manually adjustable, however, as will be appreciated, electric or fluid motors can be used to power one or both of the angles of rotation that are used to set the jetting direction at an angle. Further, the electric and fluid motors can be placed under program control of the computer 16 or the motion controller 26. An example of a dispensing system having a first programmable axis of angular motion about a Z axis and a second programmable axis of angular motion about an axis perpendicular to the Z axis is shown and described in U.S. Pat. No. 6,447,847, which is hereby incorporated by reference in its entirety herein. U.S. Pat. No. 5,141,165 relates to a dispenser having a programmable axis of angular motion about a Z axis, wherein the dispenser has a nozzle that is pivotable about a programmable axis of angular motion perpendicular to the Z axis. U.S. Pat. No. 5,141,165 is hereby incorporated by reference in its entirety herein.
It is also known to provide multiple dispensers on one or more positioners in order to simultaneously dispense a viscous material. In another embodiment shown in
In still further applications, the angle of the jetting direction can be changed between passes, which may help maintain a minimal wetted area. For example, after an underfilling operation, one or more additional passes may be made to form a fillet 85 (
Jetting the viscous material at an angle to the substrate 36 has many advantages. First, jetting the droplets 37 increases the accuracy and repeatability with which the viscous material can be applied into a corner area between a substrate surface 80 and a chip sidewall 82. Further, with the impact forces of the droplets 37 directed into the corner adjacent the gap 84, the wetted area of the viscous material on the substrate 80 is reduced. A smaller wetted area provides a potential for increased device density on the substrate 36 and thus, making the substrate smaller. In addition, increasing the speed at which the dispenser 40 is moved by the positioner 14 often results in an increase in the wetted area. By jetting at an angle, the positioner speed can be increased without increasing the size of the wetted area when compared to nonangular jetting. Therefore, potentially the cycle time for an underfill process can be shortened, thereby reducing costs. Further, the greater viscous material deposition accuracy and repeatability also often means that less viscous material will be used, which also translates into a savings in cost.
While the invention has been illustrated by the description of one embodiment and while the embodiment has been described in considerable detail, there is no intention to neither restrict nor in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those who are skilled in the art. For example, in the described embodiment, in
In the described embodiments, the device 39 is shown as having sidewalls 82, 86 substantially perpendicular to the substrate surface 80; however, as will be appreciated, in other applications, one or more of the device sidewalls can be nonperpendicular, curved or some other shape. In addition, the positioner 14 is shown and described as having two mutually perpendicular and linear axes of motion. Again, as will be appreciated, in other applications, the one or more axes of motion of the positioner can be nonlinear.
In the described embodiments, the application of a viscous material is shown in applications relating to the mounting of devices 39 on a substrate 36, such as, underfilling and forming a substrate. As will be appreciated, in various embodiments shown and described herein for jetting a viscous material at an angle can also be used to apply a conformal coating to the device 39 and/or substrate 36. For example, referring to
Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims, which follow.
