Background of the Invention

This is a continuation-in-part application of U.S. Serial No. 931,786, filed August 18, 1992.

This invention pertains to a method and apparatus for dispensing fluid materials, and more particularly to a method and apparatus for dispensing flux on a surface such as a printed circuit board. The invention is particularly applicable to dispensing a low solids flux and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed with other types of fluxes.

In fabricating a printed circuit board (PCB) , which defines a substrate surface for a printed circuit assembly, three general types of boards are frequently encountered. The first is known as a surface mount board in which only surface mount components are used. A method of securing these components to the board is known as reflow soldering where solder paste is placed on the board, and then the surface mount components located as desired. The solder paste is cured as the board is heated to reflow the solder and complete the electrical connection. Thereafter, the board is cleaned, and if a double-sided surface mount assembly is required, the same process is applied to the opposite side of the board.

The second type of board uses through hole components. As the name implies, these electrical components have leads that extend through holes or openings in the board. The leads are soldered to complete the electrical connection.

In a mixed technology board, a combination of

used. The surface mount components are assembled and soldered as described above. After the surface mount components are secured to the first side of the board, the through hole components are then located on the board with the component leads extending through openings in the board for a subsequent soldering process. If a double-sided assembly is envisioned, the board is inverted and the surface mount components are applied to the second surface. In either situation, a soldering operation is required on one surface, typically the bottom surface, of the board. One common soldering process is known as wave soldering in which molten solder is pumped into a wave form and a conveyor assembly transports the board thereover. A surface of the board contacts the peak of the wave and the solder wets the protruding component leads The solder is drawn up into the through holes to effectively and securely establish an electrical connection. The soldered board, including surface mount components previously adhesively secured to the board, requires subsequent cleaning. The entire soldering process is actually comprised of three separate and essential steps which are normally performed within a single machine. These steps include (i) flux application, (ii) preheating the board, and (iii) soldering. Soldering flux is generally defined as "a chemically and physically active formula which promotes wetting of a metal surface by molten solder, by removing the oxide or other surface films from the base metals and the solder. The flux also protects the surfaces from reoxidation during soldering and alters the surface tension of the molten solder and the base metal."

(Institute for Interconnecting and Packaging Electronic Circuits (IPC), ANSI/IPC/SF-818, "General Requirements for Electronic Soldering Fluxes", 1988, 3.1.18). As described in depth in CLEANING PRINTED WIRING ASSEMBLIES IN TODAY'S ENVIRONMENT, edited by Les Hymes, and published by Van Nostrand Reinhold, a printed circuit board must be cleaned

with flux to effectively prepare the board for soldering and properly wet the components.

Four general types of fluxes are in common commercial use. Of these, rosin based fluxes are the most widely used, even though they normally require a subsequent cleaning operation to remove rosin flux residue on the board. The residue can adversely impact subsequent testing of the printed circuit board.

Another major category of fluxes includes water soluble fluxes which, as the name suggests, are designed to be cleaned in an aqueous solution. For a variety of reasons, though, this technology is not yet readily accepted.

Likewise, a third category is synthetic activated fluxes, which are decreasing in demand for a number of reasons. For example, the residues must be removed with chlorofluorocarbon (CFC) based cleaners which raises environmental concerns.

A fourth type of flux receiving greater attention in light of the environmental concerns is termed a low solids flux. Low solids fluxes contain small amounts of solids, e.g., five weight percent or less. Use of low solids fluxes are intended to limit the amount of residue remaining on the board after soldering is completed so that subsequent cleaning operations can be eliminated.

As alluded to above, commercial cleaning operations typically employ CFC's. Studies presently indicate that use of CFC's destroy, or adversely contribute to the destruction of, earth's stratospheric ozone. Thus, elimination of subsequent cleaning operations for printed circuit boards will, in turn, address environmental concerns of ozone depletion associated with post soldering cleaning processes.

Generally speaking, fluxes commonly incorporate a solvent, vehicle, activator, surfactant and antioxidant. The solvent is the liquid carrier for the flux ingredient.

the solvent. The vehicle component of the flux serves as a high temperature solvent during the subsequent soldering operation. The activator, on the other hand, removes contaminants such as oxides to present a wettable surface for the soldering operation. The surfactant encourages solder wetting while the antioxidant limits reoxidation of the component leads.

Known structures and methods for applying flux to a printed circuit board are described in U.S. Patent No. 4,821,948. These conventional techniques include liquid wave, foaming, brushing, or spraying, all of which are deemed to be deficient in one manner or another in achieving the overall goals of uniformity and effectiveness of flux application. Focusing more particularly on low solids fluxes, three methods are commonly used. The flux can be applied as a wave in a manner analogous to the wave soldering technique. An open bath of flux is pumped into a wave form and the board surface passed into the wave crest. In addition to problems associated with flux being inadvertently placed on the top of the board, the uniformity of application and ability to precisely control the amount of flux application can be problematic.

Moreover, since the bath of flux is exposed to atmosphere, the specific gravity of the flux is subject to change. With low solids fluxes, conventional techniques of controlling specific gravity with automatic density controllers is ineffective since the low amount of solids in the composition is sensitive to slight changes of solvent.

A foam fluxer may alternately be used. This flux application technique also has an open bath of flux through which air bubbles are passed to form a foam layer. The board is passed through the foam layer to apply the flux to the desired surface. Since this method also requires an open reservoir, control of the specific gravity of the flux

the foam fluxing technique lacks the desired uniformity and precision of application, along with the potential for flux to be deposited on the upper surface of the board.

The third commonly used technique of applying low solids flux to a board is spraying. The '948 patent describes one type of high velocity spray in which the flux is ultrasonically atomized. More particularly, the flux is dispersed into tiny droplets and directed into the path of a substantially laminar air flow to allegedly provide uniform flux application. An enclosing structure collects and exhausts the vapors that result from this flux application. Other sprays in which the flux is atomized, or a rotating drum spray in which the flux is atomized by an air knife from the surface of a rotating mesh drum, are known in the art. These known techniques waste a substantial amount of the flux sprayed from the nozzle in an effort to completely and effectively coat the surface of the printed circuit board. In fact, a significant amount of flux is sprayed past the board and must be removed from the work area. Increased costs are then associated with removing the flux, i.e. filtering, from the air exhausted from the work surface.

If the flux-laden air spray is not ventilated or exhausted from the work area, the upper surface of the board can be coated with flux. This, of course, is undesirable. Moreover, in addition to the costs of the filtering apparatus required because of the overspray, the filters must be frequently cleaned at a substantial cost in downtime and maintenance. Additionally, the flux supply must be more frequently replaced or resupplied as a result of the overspray problem. In fact, even with expensive filtering apparatus associated with known flux spraying arrangements, the work area is typically enclosed in a metal chamber or cabinet that precludes visual monitoring of the flux application. This is primarily attributed to the flux laden air coating the interior of the cabinet and

As the spray nozzle and board move relative to one another according to the various spray techniques, the lack of uniformity of flux application is apparent. A phenomenon known as shadowing results from this relative motion and can be briefly described as areas adjacent a protruding component that fail to receive any flux, or an insufficient amount of flux, because of the relative motion. This is oftentimes categorized as a lack of uniform application, but is itself, a more particular specie of problem associated with the spray application.

Prior spraying techniques do not lend themselves to promotion of "wicking", which results from capillary action due to surface tension. Fluid material naturally tends to adopt the configuration having the lowest surface tension, and it is observed that prior techniques do not take advantage of cohesive and adhesive forces that result in flux material being attracted to desired soldering locations.

Still another problem associated with known flux spraying apparatus is that electrical components are housed in the work area and thereby exposed to the flux. Since a major component of many commercially used fluxes is alcohol, it is desired to limit exposure between the electrical components and the flux. The subject invention is deemed to provide a new apparatus and method that overcomes all of the above referred to problems and others and provides for an even, uniform, and precisely controlled application of flux to a surface.

Summary of the Invention

According to the present invention, there is provided a method and apparatus of applying flux to a surface at a high rate of speed, in the general range of twenty (20) to ninety (90) inches per second, with the

preferred speed on the order of approximately forty (40) inches per second.

According to another aspect of the invention, the flux is dispensed in a thin stream. According to still another aspect of the invention, a dispensing tip is tilted at an angle relative to the board and, if desired, a second dispensing tip disposed generally orthogonal to the first dispensing tip is passed over the same general work path to coat a predetermined area twice.

According to yet another aspect of the invention, the dispensing apparatus includes means for incrementally advancing one of the dispensing head and the printed circuit board. According to a still further aspect of the invention, the dispensing head is reciprocated in a direction generally transverse to the direction of movement of the circuit board.

Another aspect of the invention is the elimination of electrical components in the flux application area.

Still another aspect of the invention is the ability to capture any limited overspray that may occur. A principal advantage of the invention resides in a uniform, precisely controlled application of flux to a printed circuit board.

Another advantage of the invention is found in the ability to address the shadowing problem encountered with prior art arrangements. Still another advantage is realized in the use of a low solids flux of low viscosity to address environmental concerns, and the ability to precisely apply flux to the printed circuit board.

Yet another advantage is the high rate of speed of flux application that dispenses an extremely thin layer of flux and, if desired, permits multiple passes over a

Another advantage of the invention resides in the ability to accurately coordinate the position of the dispensing head with the printed circuit board so that the dispensing operation can be accurately actuated in response to the dispensing head position.

Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.

Brief Description of the Drawings

The invention may take physical form in certain parts and arrangements of parts, preferred embodiments and methods of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:

FIGURE 1 is a perspective view of a mixed technology printed circuit board that incorporates surface mount and through hole components;

FIGURE 2 is a schematic illustration of selected steps in the printed circuit board assembly process, namely the flux and solder application stages;

FIGURE 3 is an elevational view of one embodiment of the flux dispensing apparatus according to the subject invention;

FIGURE 4 is a side elevational view taken from the right-hand side of FIGURE 3;

FIGURE 5 is an enlarged perspective view of the dispensing head applying flux to the surface of a printed circuit board;

FIGURE 6 is a greatly enlarged elevational view showing the use of two dispensing tips tilted at an angle relative to a printed circuit board;

FIGURE 7 is an elevational view of another preferred embodiment of the flux dispensing apparatus

FIGURE 8 is a side elevational view taken generally from the right-hand side of FIGURE 7;

FIGURE 9 is an enlarged, detailed view of a dispensing head disposed below a printed circuit board as generally shown in FIGURE 7;

FIGURE 10 is a longitudinal cross-sectional view of a preferred dispensing tip;

FIGURE 11A is a perspective view of a manifold arrangement for providing multiple streams of flux; FIGURE 11B is a top plan view of the manifold; and

FIGURE 11C is an end view of the manifold of FIGURE 11B.

Detailed Description of the Preferred Embodiments and Method

Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiment and method of the invention only and not for purposes of limiting same, the FIGURES show a printed circuit board A which passes through an assembly process B that includes a fluxing system or station C, preheater D, and soldering system or station E. More particularly, a mixed technology printed circuit board A is illustrated in

FIGURE 1 and includes a board 10 comprised of an insulating material having a first or upper surface 12 and a second or lower surface 14. A series of through holes 16 receive leads 18 of a through hole component 20. The insulating material and through holes include selected areas of metal material associated with the component leads for establishing electrical communication as desired. Details of the printed circuit board technology in that regard are well known in the art, forming no part of the subject invention, so that further discussion is deemed unnecessary.

Additionally, surface mount components 26 are associated with the mixed technology circuit board. Again, the particulars of the surface mount component form no part of the subject invention and are merely illustrated and described herein to illustrate the applicability of the subject invention to a printed circuit board that employs only through hole components, or a mixed technology board. It is contemplated that the subject invention may also find application with printed circuit boards that have surface mount technology only. For example, the process and apparatus to be described below would dispense a flux on the surface, then potentially use a paste that has a reduced amount of, or lacks any, flux in the paste associated with surface mount technology. Leads extend outwardly from the ^" board 10 and are adapted for soldering to complete the connection with the metal layers. One well known type of soldering process passes the board over a wave of molten solder E so that each component lead is coated to complete the electrical connection. As best represented in FIGURE 2, prior to passing over the wave solder station E, the board surface 14, for example, is passed through a flux station C. A soldering flux is dispensed onto the selected surface, and as the board proceeds rightwardly as shown, the solvent is driven off at the preheating station D by means of conventional heating elements 28. The flux prepares the surface for the molten solder, removing oxides and other contaminants, and preparing the surface to promote solder wetting. The flux may also include an antioxidant that prevents further oxidation between the flux station and the soldering step.

One embodiment of the flux station C is more particularly illustrated in FIGURES 3 - 6. As shown there, a supporting framework 40 positions one or more dispensing heads 42 a predetermined distance above conveyor line 44. The conveyor line 44 may be of any well known structure, although a referred arran ement is one manufactured and

sold by Automation Technologies. As shown, the conveyor follows a closed loop path in which opposite edges 44a, 44b (FIGURE 4) of the conveyor rotate about horizontal axes and include inner, facing edges that support the board 12 in a generally horizontal position as it proceeds through the flux dispensing apparatus (leftwardly to rightwardly in FIGURE 3) .

This particular conveyor is a simple, constant speed conveyor that feeds the printed circuit board beneath the dispensing head. Once located there, further movement of the board is terminated while the dispensing head proceeds through a flux applying routine, the movement of the head preferably being controlled by a microprocessor 46. For example, the dispensing head is an X - Y axis actuated assembly that incrementally moves the dispensing head over the stationary board along a first axis (X) generally parallel to the conveyor line. A second actuator moves the dispensing head laterally over the board along a second axis (Y) . Because of the high rate of speed associated with the dispensing head as it travels laterally across the board, the entire dispensing operation can still fall within accepted rates of board throughput speed and remain compatible with commercially accepted rates of speed. Once the lateral travel of the head is completed, the dispensing head is then incrementally advanced along the first axis to position the dispensing head over another selected work path of the board. This process is continued until flux is dispensed over the desired portions of the board. Alternatively, more expensive conveyors can be used that incrementally feed the board through the flux station. For example, the board is moved in one-eighth inch increments so that, when stationary, multiple passes of the dispensing head will coat the selected surface with the flux. The dispensing head under this alternate arrangement need only be actuated in a lateral direction

the board and dispensing head (along the first axis) is provided by the more complex and sophisticated conveyor system. Again, suitable microprocessor control and an associated control panel 46 is associated with the conveyor line and actuating mechanism for the dispensing head to control movement of the board through the flux station, as well as dispensing of flux on the selected portions of the board surface.

According to the subject invention, the overall throughput speed of conveyor line 44 is still closely maintained at the approximate rate of one inch per second, although other rates can be attained as may be required. More importantly, though, the printed circuit board is incrementally advanced through the fluxing station or the dispensing head is incrementally advanced over the board surface. That is, the board is accelerated, stopped, flux is applied, and the board accelerated for the next application of flux. Thus it will be understood that the application of flux to the board will be entirely completed while the board is stationary, or selected regions of the board will receive flux and the board incrementally advanced for another application of flux to a different region, etc.

As best illustrated in FIGURE 4, the dispensing head 42 travels generally transverse (along the second axis) to the movement of the printed circuit board on conveyor line 44 (parallel to the first axis) . Thus, as the board is advanced by the conveyor, and when it reaches a stationary state, the dispensing head 42 is reciprocated at a high rate of speed transversely over the surface of the printed circuit board.

Through use of a low solids flux, and dispensing at a high rate of speed ranging between 20 and 90 inches per second, but preferably on the order of 40 inches per second, a very thin, non-atomized, continuous stream of flux is applied or coats the selected surface of the board. For exam le tests v

in a thin line approximately 0.040 inches in width and at a flow rate of 0.02 cc's per second provides an application of flux at the rate of 0.0006 g/in ² . Since a low solids flux material is used, multiple passes can be made over generally the same work path. This permits a second coating of flux without extending beyond accepted limit rates of flux application.

As illustrated in FIGURE 5, the board 10 is incrementally advanced rightwardly while the dispensing head 42 is reciprocated fore and aft. The dispensing head includes a needle or tip 50 that dispenses or applies the low solids flux in a continuous stream 54. The opening in the tip has an inner diameter in the range of 0.010 inches or less, and preferably on the order of 0.004 inches. Again, since the dispensing head is moved at a high rate of speed on the order of 40 inches per second, multiple passes can be made. Additionally, because of the incremental movement of the printed circuit board, an even and uniform application of the flux is achieved. The thin stream of flux 54 naturally flows outwardly as represented by the dotted lines in FIGURE 5. By carefully controlling the incremental movement of the tip 50, the next adjacent stream of flux can be precisely located so that the outward flow abuts with the flow of flux from a prior dispensed stream, slightly overlaps therewith, or has a large amount of overlap as desired or required for specific applications. If the adjacent stream is applied before the solvent is driven off, for example within two seconds, the outward flows of adjacent streams will merge and the applied streams become virtually indistinguishable, providing a uniform application of flux to the board surface.

With continued reference to FIGURES 3 - 5, and additional reference to FIGURE 6, a multi-tip dispensing head will be described. One preferred arrangement includes a pair of needles 50a, 50b secured to one or more

tilted or angularly disposed from perpendicular relative to the surface of the printed circuit board 12. As shown in that FIGURE, the printed circuit board is incrementally traveling on a path extending out of the page. The dispensing head, on the other hand, moves transverse to that path as indicated by the arrow 52. On the first pass across the surface 12, a layer of flux 54 is applied. Because of the protruding nature of the electrical component 20 or 26, and because of the relative speed of the dispensing head relative to the board, a phenomenon known as shadowing occurs. Thus as the dispensing head moves rightwardly, the horizontal surface represented by numeral 56 will receive a small amount, if any, of the layer of flux 54 as it is applied. Upon leftward reciprocation of the dispensing head, the-second layer of flux 58 will eliminate the shadowing effect of area 56.

Thus, a more even distribution of flux is achieved by coating the surface twice through use of multiple passes.

Additionally, tilting the needles 50a and 50b relative to perpendicular eliminates problems associated with shadowing. It also assures that the flux will be applied slightly beneath the components mounted on the board.

The flux can be dispensed from the head through use of a syringe type dispenser, or alternatively a valved arrangement can be used. Under either arrangement, the dispensing of flux in a continuous, thin stream across the surface of the printed circuit board can be achieved. Further, by control of the dispensing head with the microprocessor, timed regulation can dispense flux over predetermined areas. For example, on a single pass across the width of a board, flux can be alternately applied, shut off, and applied as the tip proceeds across the surface. Again, this leads to a more uniform application of flux and only applies flux where desired. Also by virtue of the dispenser head, problems associated with open reservoirs of

gravity of the flux can be maintained since the flux is not exposed to the environment until it leaves the tip 50 of the dispensing head.

Control of flux application may also be enhanced by preheating the board so that the flux stays in place when applied. That is, some of the solvent will be driven from the flux and it will have a tendency to remain in place on the board and not be as prone to spreading if the board is preheated. This adds to the precision of dispensing a thin stream of flux on the board, particularly when multiple passes are used.

Although FIGURES 3 -6 show the dispensing head disposed above the board at a predetermined height of approximately 0.040 inches to 0.30 inches and dispensed at a rate on the order of 0.02 cc/sec to apply the flux at a rate of approximately 0.0006 g/in ² , it is contemplated that the above described structure and process is equally applicable to an arrangement where the flux is dispensed from a head located beneath the board as shown in the embodiment of FIGURES 7-9. Like numerals will refer to like elements while new numerals will refer to new elements. The parameters may be altered somewhat to accommodate the reversed position of the dispensing head but the application rate will be generally the same. Moreover, in accordance with the embodiment of FIGURES 7 -

9, the board will be maintained stationary during the dispensing process rather than being incremented through the flux applying station as described above. Instead, the dispensing head will traverse the board as required to coat the lower surface.

Referring to FIGURE 7, the flux applying station C receives a board 10 to which flux is to be applied to the lower surface 14. The location of the board is sensed at the input end 60 of the flux dispensing apparatus by a sensor 62. A signal is then relayed by the sensor to logic controller 64 (FIGURE 8) preferably mounted in a closed

chamber 66 is clear or open, the logic controller actuates the conveyor 44 to advance the board into the work chamber. A stop 68 is disposed in the chamber and sends a signal to the logic controller that the board is positioned for flux application.

The dispensing head 42 is preferably located at one corner of the board and a thin, non-atomized stream of flux is emitted from the dispensing head onto the lower surface of the board. The dispensing head will travel a predetermined path while the board is stationary in the work chamber to coat the lower surface. For example, as shown by arrows 70 in FIGURE 7, the dispensing head will travel through a stroke generally parallel to the X axis in response to a first or stroke motor 72 which is preferably a servo controlled motor. The servo controlled motor provides positive feedback, or encoder signals, to the logic controller so that the precise location of the dispensing head can be monitored, and the actuation and de- actuation of the valve controlling dispensing of the flux be tied to the position of the dispensing head. The dispensing head is then indexed or moved laterally by a second or incrementing motor 74 to a new location along the Y axis (FIGURE 8) , and prepared for movement by the stroke motor along the X axis. This process is repeated until the lower surface of the board is coated with flux as desired.

The incrementing motor is also preferably a servo controlled motor that provides a feedback signal to the logic controller for accurate determination of the position of the dispensing head. A reservoir 80 is located in the closed work chamber 66 to provide a ready supply of flux. The flux is pressurized, for example between one and fifteen psi, depending on the size and number of dispensing tips. The flux then passes through a filter 82 to remove any particles that could potentially clog or block the dispensing tip opening. For example, the filter could revent art c

passing through fluid line 84 that connects the reservoir to the dispensing tip. Still other filter sizes can be used with equal success.

An electronically actuated valve 86 is preferably used to regulate flow of flux from the reservoir to the dispensing head. The valve is actuated and deactuated by the logic controller in response to the location of the dispensing head. The electronic portion of the valve is mounted outside the work chamber because of the desire to separate any electrical components from the flux because of its flammable nature.

As described above with respect to the embodiment of FIGURES 3-6, the dispensing head includes openings of extremely small diameter so that a thin stream of flux can be directed toward the board. Recent use of tips formed from sapphire provide an extremely hard material that provides durability and a smooth surface for forming a very consistent, thin stream that can apply flux into small diameter via openings in a printed circuit board. For example, as shown in FIGURE 10, the dispensing head has a stainless steel tube 90 that is closed at one end with a sapphire tip 92. Preferably, the sapphire tip has a rounded or tapered edge 94 as it proceeds from the tube to opening 96 in the sapphire. The rounded edge prevents flux from accumulating on the sapphire tip so that the opening does not become clogged, which is of particular importance when the flux is dispensed from below the board. The sapphire tip also adds the advantages of (i) forming very small and reproducible openings, (ii) very smooth surface openings, (iii) providing a hard material that is very durable, (iv) tapering the opening 96 at the inlet end 98 for smooth, air-free flow, and (v) the ability to position a number of tips closely together. Moreover, dispensing tip opening diameters in the range of 0.0005 to 0.0080 inches can be used to provide even greater control of the application of flux to the board.

Moreover, use of such small openings may permit a single dispensing head to have multiple separate tips where the openings are appropriately spaced apart to form a multi-tip dispensing head. Alternatively, a manifold arrangement as shown in FIGURES 11A - 11C can be used to simulate a multi-tip dispensing head. Several openings 96 in a rectangular sapphire plate 100 can be spaced apart as desired to act as a multi-tip head. The plate is still preferably tapered as shown at 102 in FIGURE 11B to prevent clogging or accumulation of flux over the openings 96. A common fluid inlet 104 (FIGURE 11C) provides flux from fluid line 84 to the manifold arrangement.

The minute size of the dispensing tip openings provide better and more accurate, uniform application of flux to the board which, in turn, results in improved, consistent soldering of the leads. Moreover, better filleting of solder up the lead wires is achieved with this flux dispensing arrangement. Via holes or openings are also coated with flux for more consistent solder filling. Material utilization is also vastly improved because of the precise application of flux to the board. This offers greater environmental benefit and higher operational cost savings. The closed material system provides consistent flux composition without the need for titration and solvent addition.

This arrangement also eliminates the requirement for an air curtain or spray associated with known commercial flux applicators. Those arrangements must provide a suitable exhaust and filtering system to draw the flux laden air away from the board and prevent it from being deposited on the top surface of the board. With the present invention, any flux that bypasses the board is minimal in amount and can be controlled by a means for capturing the flux, such as a layer of absorbent material 110. The absorbent material is mounted over the board adjacent the flux applying area. Since the flux has a lar e ercenta e o a coho

absorbent material can retain the remaining flux componen without frequent changeover of the absorbent materia This also contributes to a clean work chamber so that se through, plexiglass doors 112 can be used with t dispensing apparatus to allow visual monitoring of the fl station.

The work chamber will still be ventilated. It contemplated, though, that the precision control of t flux application will not require the labor intensi maintenance of known complex filter arrangements in oth flux systems.

The invention has been described with referen to the preferred embodiments and method. Obviousl modifications and alterations will occur to others upon reading and understanding of this specification. It intended to include all such modifications and alteratio insofar as they come within the scope of the append claims or the equivalents thereof.