Coating apparatus – Projection or spray type – Work-supported and guided carriage
Reexamination Certificate
1999-05-10
2001-07-17
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
Work-supported and guided carriage
C118S300000, C118S323000, C156S356000, C239S597000, C239S601000
Reexamination Certificate
active
06261367
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of liquid material dispensing and, more particularly, to an apparatus and method for dispensing liquid or viscous materials such as solder fluxes, adhesives, epoxies or other materials onto an electronic circuit substrate.
BACKGROUND OF THE INVENTION
Liquid dispensing systems have become an integral part of the electronics manufacturing process for depositing underfill, encapsulants, solder fluxes, surface mount adhesives, conformal coatings and other materials onto a substrate, such as a printed circuit board. Each liquid dispensing system used in the electronics manufacturing process has a particular dispensing characteristic that is determined in large measure by the desired liquid dispense pattern on the substrate, the liquid flow rate and/or liquid viscosity of the dispensed material, and the desired electronic component assembly throughput through the dispensing system.
For example, in the assembly of ball gate arrays (BGA's) and other electronic components onto a ceramic or FR-4 substrate, the component must be soldered onto the substrate to form the necessary electrical interconnections. As each component occupies a predetermined area on the substrate, the liquid dispensing system must have the capability to dispense liquid or viscous material in a controlled manner within the selected component areas. Typically, the liquid dispenser is mounted on a movable platform to provide automated and accurate movement of the liquid dispenser in three dimensions relative to the substrate with the aid of a machine vision system.
Prior to the component soldering process for establishing the electrical interconnections, it is often necessary or at least desirable to dispense a layer of solder flux onto a substrate within rectangular areas associated with each component. To provide this capability, liquid material dispensers have been developed in the past that use filled syringes or reservoirs of solder flux, and dispensing valves to dispense droplets of flux material onto the substrate in a controlled manner with up to 25,000 to 40,000 dots of fluid per hour for a typical dispenser platform. These liquid dispensers, known as “dot jetting” dispensers, are programmed to dispense an array of liquid or viscous material droplets within each selected rectangular area which are then allowed to flow into contact with each other to form a generally rectangular thin layer of flux within the component area. However, notwithstanding the advances made in the electronics manufacturing process through “dot jet” dispensing of solder flux onto a substrate, the “dot jet” dispensing process has several drawbacks or limitations.
For example, in the “dot jet” process, each dispensed droplet has a generally circular configuration. To effectively cover or form a liquid layer in a rectangular area on the substrate, material flow of adjacent “dots” or “dot” overlap is required. These dispensing techniques can result in too much material being dispensed within the predetermined component area, or surface tension changes in the dispensed material that do not allow the “dots” to flow as desired. Moreover, due to the relatively small diameter of the “dots”, more dispense cycles are required per unit area of coverage which can result in reduced throughput of electronic assemblies through the dispensing system.
Thus, there is a need for a liquid dispensing system and method that more effectively forms generally rectangular liquid layers on a substrate. There is also a need for a liquid dispensing system and method that improves throughput of assemblies through the dispensing system for forming rectangular liquid layers on a substrate.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing and other shortcomings and drawbacks of liquid dispensing systems and methods heretofore known for forming generally rectangular liquid layers on a substrate. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The liquid dispensing system of the present invention is particularly adapted for forming generally rectangular liquid layers on an electronic substrate. The dispensing system includes a nozzle tip that is configured to dispense liquid material droplets that elongate in pattern width and in pattern length during their flight toward the substrate. The elongated droplets impact the substrate and contact adjacent droplets to form generally rectangular liquid layers within predetermined component areas on the substrate.
The nozzle tip has an upper end adapted to be placed in fluid communication with an outlet end of the liquid dispensing system, and an opposite lower end adapted to face the substrate. An upper elongated groove or cavity is formed on the upper end of the nozzle tip, and a lower elongated groove or cavity is formed on the lower end. The upper and lower grooves extend inwardly into the nozzle tip and intersect each other to form a liquid dispensing outlet. Preferably, the liquid dispensing outlet is configured to provide liquid impingement at the dispensing outlet for dispensing droplets of liquid material that elongate in a plane generally transverse to the direction of travel of the droplets in flight toward the substrate.
The nozzle tip includes a pair of oppositely disposed chamfered end portions formed proximate the lower end of the nozzle tip that define opposite terminal ends of the lower groove. Each chamfered end portion includes a pair of inclined walls that extend outwardly and away from the lower end of the nozzle tip. A nozzle tip holder is mounted adjacent the outlet end of the liquid dispensing system for supporting the nozzle tip. The nozzle tip holder includes opposite pairs of inclined walls that form generally linear extensions of the inclined walls formed on the nozzle tip. A nozzle cap is mounted adjacent the outlet end of the liquid dispensing system for supporting the nozzle tip holder.
The liquid dispensing system of the present invention eliminates the need to provide for dwell to allow droplets to flow into contact with each other, and also eliminates the need to overlap adjacent droplets to form a generally rectangular layer of liquid material on the substrate, thereby resulting in enhanced throughput of electronic assemblies through the dispensing system.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.
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Crispino Richard
Lorengo J. A.
Nordson Corporation
Wood Herron & Evans LLP
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