Measuring and testing – Liquid analysis or analysis of the suspension of solids in a...
Reexamination Certificate
1999-02-22
2001-11-27
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
C427S008000, C382S152000
Reexamination Certificate
active
06321591
ABSTRACT:
FIELD OF THE INVENTION
This invention generally pertains to test equipment for sensing, analyzing, and measuring spray from a liquid dispensing system, such as in the electronics industry. The invention finds particular application as a device for measuring the even distribution of flux dispensed from a flux applicator system.
BACKGROUND OF THE INVENTION
A printed circuit board (PCB) generally includes a multi-layered board having electronic components, such as chips, transistors, resistors, etc. mounted thereon. Conductive traces formed on the layers of the board connect the electronic components together to form an electronic circuit. The electronic components may be a surface-mount type where the legs of the components are mounted on top of conductive pads. Alternatively, the electronic components may be a through-hole type where legs of the components extend through vias (small holes) within the PCB.
Wave solder machines are used to mount the electronic components to the PCBs. The wave solder machines have multiple stages including a fluxing stage, a preheating stage, and a wave solder stage. The fluxing stage applies flux to the PCB, as further described below. The preheating stage raises the temperature of the PCB in preparation for soldering. And the wave solder stage applies solder to the PCB, thereby bonding the electronic components to the PCB.
Liquid dispensing systems are used during the fluxing stage of the wave solder machine. Before soldering the electronic components to the PCB, flux is applied to remove or facilitate removal of oxides from metal parts, such as the legs of the electronic components. The flux also prevents further oxidation of metals during soldering. Flux applicator systems are a particular type of liquid dispensing system wherein a reciprocating or fixed spray nozzle system ejects atomized flux in a precise pattern over an entire side of the PCB. The flux applicator systems typically are either an air-pressure type or an ultrasonic type. Both types of flux applicator systems have potential problems. The air pressure-type flux applicator systems generally produce a number of relatively large drops of flux traveling at high velocities. At least some of these high-velocity drops bounce off of the PCB, rather than settling on the desired surface. Ultrasonic-type flux applicator systems use high-frequency sound waves created by piezoelectric crystals. Liquid is introduced onto an atomizing surface through a feed tube and is directed toward the PCB by forced air. The vibrational amplitude of the atomizing surface is carefully controlled. If the amplitude is too high, a condition known as cavitation occurs where large droplets of fluid are ejected. If the amplitude is too low, the energy is insufficient to produce atomized drops.
Applying an even distribution of flux is important when producing the PCBs. If too little flux is applied to any portion, oxidation can occur during the soldering process. On the other hand, too much flux requires cleaning of the PCB, which can be expensive and slow the manufacturing process. For example, cleaning a PCB requires expensive cleaning equipment, disposal of chemical waste, and time for drying the PCBs. To ensure that an even distribution of flux is applied to the PCBs, a test PCB is traditionally is sent over the flux applicator system with thermal paper attached to the underside of the board, such as by taping. The thermal paper reacts with the flux sprayed from the flux applicator system causing the thermal paper to discolor. If the thermal paper is not completely discolored, then the flux is not being applied properly. The thermal paper may also be taped or otherwise placed on the topside of the PCB. Alternatively, cardboard may be sent through the flux applicator system to simulate a PCB. The cardboard discolors in spots where the flux is applied. Still further some companies run actual product through the wave solder machine and check if the product was properly produced. This typically requires scraping some of the product as adjustments are made to the flux applicator system.
This prior technique for testing the flux applicator system is problematic. First, the thermal paper can only detect if too little flux is applied, not if too much is applied. Additionally, the thermal paper does not adequately absorb flux well so the flux puddles and often smears before a technician can view an image formed on the thermal paper. Furthermore, the flux may be applied enough to discolor the thermal paper, but not enough to transfer through the vias in the PCB, as is needed to ensure proper soldering.
An object of the invention, therefore, is to provide a method and apparatus for accurately measuring the distribution of liquid dispensed from a liquid dispensing system.
SUMMARY OF THE INVENTION
The present invention is directed to a system and method for measuring liquid from a liquid dispensing system. In particular, the present invention is used to measure the uniformity of distribution of flux applied to PCBs in a wave solder machine. In the illustrated application, a flux measuring device is described that measures flux dispensed from a flux applicator system. The flux measuring device is a test unit that simulates a PCB. Once uniform distribution of flux is measured, different parameters in the flux applicator system can be modified to ensure that the proper flux is applied to PCBs during their manufacture.
In one aspect of the present invention, a mesh or perforate board or plate having substantially uniform thickness and sized to approximate the size of a PCB processed by the system includes a plurality of spaced-apart holes that extend through the mesh board. The holes are sized so that liquid dispensed from a nozzle that contacts the bottom surface of the mesh board enters the holes and is detected on the top surface of the mesh board. In other words, the mesh board helps to produce a visual representation of topside penetration by the flux. A cover on top of the mesh board maintains detection material uniformly in contact with the top surface of the mesh board.
In another aspect of the invention, an image is formed on the detection material due to contact with liquid that passes through the holes in the mesh board. Image processing and analysis software may be used to automatically measure whether there is a uniform distribution of flux on the detection material. Based on the measurement, the liquid dispensed from the nozzle or other parameters in the system can be modified.
Various advantages and features of novelty which characterize the invention are particularized in the claims forming a part hereof. However, for a better understanding of the invention and its advantages, refer to the drawings and the accompanying description in which there are illustrated different embodiments of the invention.
REFERENCES:
patent: 3609043 (1971-09-01), Simmons et al.
patent: 3981264 (1976-09-01), Smith et al.
patent: 5589225 (1996-12-01), Yamada et al.
patent: 5701156 (1997-12-01), Pierce
patent: 5811187 (1998-09-01), Anderson et al.
patent: 6190727 (2001-02-01), Thaggard
patent: 6265017 (2001-07-01), Hogan et al.
SonoFlux 9500, Spray Fluxing Systems brochure, 4 pages, Sep. 1995.
Ultrasonic Spray Nozzle Systems-When Precision Counts brochure, 5 pages, www.sono-tek.com
ozzles/main-nozzles.html, Jan. 27, 1999.
Ultrasonic Nozzles, Technology Overview, 4 pages, www.sono-tek.com/technology/main-tech.html, Jan. 27, 1999.
Austen Paul M.
Breunsbach Rex L.
Electronic Controls Design, Inc.
Klarquist & Sparkman, LLP
Politzer Jay L
Williams Hezron
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