US3513765A - Wet wall spray-coating chamber - Google Patents

Description

My 26, 1970 H. F. BOK 3;513,7 65

WET WALL SPRAY-COATING CHAMBER Filed March 26, 1969 5 Sheets-Sheet 1 mvmon A 50% A/A'w/P/K semmesandsemmes j ATTORNEYS May 26, 1970 H. F. BOK

WET WALL SPRAY-COATING CHAMBER- 5 Sheets-Sheet 2 Filed March 26, 1969 w rm I I W 1 M 4/? was: *8

mvmon H. H a

F/A F 50k BY semmesardsemmes ATTORNEYS May 26, 1970 H. F. BOK

WET WALL SPRAY-COATING CHAMBER 5 Sheets-Sheet 3 Filed March 26 1969 INVENTOR HIA/A/F/K A 504 v BY semmesmrsemmes ATTORNEYS May 26, 1970 H. F. BOK

WET WALL SPRAY-COATING CHAMBER 5 Sheets-Sheet 4 Filed March 26, 1969 semmesandsemmes ATTORNEYS May 26, 1970 H. F. BOK

WET WALL SPRAY-COATING CHAMBER 5 Sheets-Sheet 5 Filed March 26, 1969 mvsmon #i/XOP/A 5 50% BY semmesandsemmes ATTORNEYS United States Patent WET 9 Claims ABSTRACT OF THE DISCLOSURE Wet wall chamber for controlling a spray coating environment so as to eliminate the effects of overspray and bounceback of spray dust particles, particularly a structure for circulating solvent for the spray coating as a pluraltiy of staggered downwardly flowing streams, defining a baflle at one end of the chamber, and simultaneously flowing solvent downwardly on the inside inclined roof of the chamber.

CROSS-REFERENCES TO RELATED APPLICATIONS A continuation-in-part of Method for Controlling a Spray-Coating Environment (Ser. No. 676,599), filed Oct. 19, 1967, now Pat. No. 3,475,202. In the parent application there is disclosed the method of flowing solvent as a plurality of overlapping, staggered channels at one end of the environment. The present application is directed to specific structure for the Wet wall baffle and for a plurality of solvent nozzles addressing themselves to the inclined interior roof of the environment.

BACKGROUND OF THE INVENTION Field of the invention Control of spray coating of photoresist and like materials on printed circuit boards, semiconductor and microsurface wafers is conventionally conducted within a filtered laminar-flow air environment. This filtered laminar air flow limits somewhat the suspension of impure particles within the environment, but does not guarantee the full removal of overspray and bounceback particles. The present application is directed to structure for removal of overspray and bounceback particles by precipitation in solvent flowing as a wet wall baffle at one end of the environment, flowing on the inner surface of the roof of the environment.

Description of the prior art Davis, 2,155,932; McGraw, 2,217,345; Erikson, 2,259,- 626; Norris, 2,848,353; Umbricht, 2,981,525.

The foregoing prior art references teach generally horizontal and vertical flowing of solvent within the confines of a spray coating chamber, while horizontally flowing air perpendicularly to flowing of Solvent. See for example, Erikson and Umbricht. McGraw shows flowing of solvent on all vertical walls of the conveyor. Norris teaches flowing of solvent over the walls and floor of the spray coating booth. Davis, also, shows flowing of solvent over the interior walls of the chamber. None of the prior art devices show flowing of laminar air through a plurality of staggered overlapping channels as an end baflie nor a specific structure for elfectively flowing solvent over the entire interior walls of the environment. The present application is directed to this structure.

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SUMMARY OF THE INVENTION The present invention is directed to a specific bafile structure including individual bafiles and nozzles for feeding of solvent onto the baflles, as well as a structure for reciprocating longitudinally a plurality of nozzles adjacent the top inclined walls of the chamber, the two structures cooperating to present a wet wall environment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a proposed spray coat ing environment controlled by the end wall baflle and inclined top wall features of the present invention;

FIG. 1A is a view from the right side of FIG. 1;

FIG. 2 is a transverse section, partially fragmentary, showing the end baflle;

FIG. 3 is a fragmentary perspective of the inclined top wlal nozzle reciprocating mechanism;

FIG. 4 is a schematic view showing the overlap stroke of the top wall solvent nozzles, so as to achieve thorough coating of the inclined top walls;

FIG. 5 is a fragmentary top plan of the end wall battle and solvent nozzles;

FIG. 6 is a fragmentary enlarged perspective of individual balfles affixed to the solvent feeding conduit;

FIG. 7 is a fragmentary vertical section of a proposed DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a controlled environment 50 for spray coating which, when placed in a cleanroom atmosphere, maintains cleanroom condition during'and after the spray operation. This spray chamber consists of:

(a) two wetted, sloped, side walls 20 and 22 with conveyor 46-48 feed-in opening 26 and take-out opening 28 and a slotted top opening 30 for the traversing spray gun (not illustrated);

(b) traverse mechanism 32 with nozzles 34 for wetting the sloped side walls;

(0) wetted exhaust baflle system 38 with removable, staggered baflles 40;

(d) reservoir 42 from which the wet wall liquid is pumped and in which the liquid flows back again after wetting the walls 20 and 22 and staggered baffles 40; and

(e) exhaust opening 44 behind staggered wet wall battle. The exhaust through opening 44 is of such a capacity as to establish an air flow of a minimum of linear ft./

minute. As the air is pulled from the cleanroom atmosphere in which the spray chamber 50 is placed and is flowing through the frontal opening 52, a slight negative pressure is formed inside the spray chamber 50 and the cleanroom-conditioned air is, besides being pulled through the frontal opening, in the direction of the arrow, also is pulled in through the conveyor openings 26 and 28,

as well as through the gun-slot 30 at the top of the chamber. A source of laminar flow air 67 is shown attached to the frontal opening 52 in FIG. 1A.

FIG. 2 shows a cross section of the spray chamber 50 with the pump, filter and valve controls providing the wet wall liquid circulating system. Although not indicated in FIG. 1, FIG. 2 shows the chain conveyor track 46 moving in a direction from right to left. Panel 54, placed onto chain conveyor 46 and 48, moves first through air knife portal 56. In this portal 56 are placed two slotted tubes 58, one on each side of panel 54, through which tubes 58 a precleaned compressed air flows. This air-knife system provides entry portal 56 and identical portal 60 with a positive pressure as compared to the pressure within the spray chamber 50, thus preventing overspray and bounce-back from penetrating into the portals 56 and 60.

The wet wall liquid, pumped from reservoir 62 (FIG. 2) by pump 64, is pressure fed to the traversing, round fluid stream nozzles 34 as shown in FIG. 3. As illustrated in FIG. 4, the traversing stroke is approximately 1" larger than the distance A between the flow nozzles. A round stream nozzle 34 is required since the output can be controlled to a very small flow rate without causing drips which would fall onto the surfaces to be coated. Other types of spray nozzles which form an atomized fan pattern have an inherent drip problem. Furthermore, spray nozzles using an atomization agent such as compressed air, are not acceptable since they cause a considerable amount of turbulence of the air, passing through the spray chamber 50.

The wet wall fluid 62, flowing down from the wet walls and 22 and wet bafl les 40, flow onto the top 64 of reservoir 42 and through openings 66 into the reservoir. Practical applications have shown that at least a 3 /2" distance from the underside 66 of the panel 54 to the top 64 of the reservoir is required to prevent a splash-up of wet wall liquid 62 and splashing onto the underside 64 of the panel.

FIG. 8 shows the side view of the wet bafl le system 38. This consists of identical supply tubes 68, etc., with identical nozzles 70 threaded into the tubes. Flung over the supply tubes 68 are rows of identical baffles 34. Such a row of baffles 34, illustrated in FIG. 6, is formed by connecting strip 72. The spacing between the baffles is approximately of the bafiie width. As can be seen from FIG. 5, the individual rows of baffles 34 are placed staggered so that the coating particles, suspended in the air flow, are forced to strike over the many, wetted baffle surfaces. Each nozzle 70 covers the baffle surface 74 which it faces. Since the spray pattern of the nozzle is to be contained over the surface, the baffle is provided with bent side flanges 76. In addition to confining the spray wetting, these flanges 76 form an additional air flow restriction and, therefore, increase the filtering efliciency of the total baffle system.

For fast cleaning and replacing of the nozzle 70, the solvent supply tubes 68 are made to rotate at each end, thus providing a way to turn the nozzles in an upright position. A Teflon Washer 76, illustrated in FIG. 9, between the fiared flanges of tube 78 and coupling 80, provides for proper slip-fit sealing after nut 87 has been tightened.

In FIG. 2 there is also illustrated a pressure pot 84- containing clean wet-wall liquid. During normal spray operation, the wet-wall liquid 62 which is a very slow evaporating solvent, compatible with resins used in the spray coating, absorbs the overspray and bounce-back of the sprayed coating from gun 88 and the resins go in solution. The longer the spray operation, the higher the solid content of the wet-wall 62 liquid will be. It is, therefore, necessary to flush the 34 and 70 nozzles, pipes 68 and 90 and wet- wall 20 and 22 surfaces with the clean wet-wall liquid 86, stored and pressurized in pressure pot 84. Prior to shut-off of equipment, a small amount of clean liquid 86 (cleaning cycle) is pushed and pumped through the system which washes all surfaces and assures proper wetting when spray operation is assumed.

As illustrated in FIG. 2, the wet-wall liquid return system may include air pressure conduit 106, served by pressure regulator 104 as it enters pressure pot 84. A series of three-way valves 108 and 96 may be employed to regulate solvent pressure flow from reservoir 62 through exit conduit 110. Alternatively, three-way valve 108 may close exit conduit 110 so as to push clean wet-wall liquid 86 through conduit 118 thence to nozzles 34, feeding conduits 114 and 112, as well as wet-wall feeding conduit 116. Pressure control valves 92, 9'4, and 98 may be employed, the latter valve being employed in pumping bypass conduit 120. Pump 64, together with three-way valve 108, may be utilized to recirculate wet-wall liquid directly from the reservoir bottom into nozzles 34 and 70. Also, a filter 100 may be employed together with an antipulsating device 102 used to remove pulsations in the liquid caused by the pumping action.

I claim:

1. A baflie structure for downward flowing of solvent in a spray-coating chamber of the type having a conveyor extending transversely through the chamber and an in-' clined roof comprising:

(A) a solvent reservoir within the bottom of said chamber;

(B) a plurality of vertically upstanding, longitudinally staggered and overlapping channels supported as a wet wall baffle at one end of said environment, each channel having longitudinally extending side flanges and a curvate top;

(C) a solvent circulation end conduit extending from said reservoir to the curvate top of said baflles and including:

(i) a plurality of nozzles positioned adjacent individual channels;

(ii) the curvate tops of the channels engaging said conduit; and

(D) means pressurizing said solvent so as to circulate solvent within said conduit, through said nozzles and into said channels.

2. A baflle structure as in claim 1, said solvent circula tion end conduit including a plurality of extensions later ally traversing said end of said chamber as channel and nozzle supports.

3. A baffle structure as in claim 2, said nozzles being supported upon one conduit extension and being directed toward the forward surface of a channel supported on the next adjacent conduit extension.

4. A baffle structure as in claim 3, in combination with:

(E) a roof wetting solvent dispenser including:

(i) a solvent circulating roof conduit extending axially at either side of the top of said inclined roof;

(ii) a plurality of nozzles supported upon the roof conduit and directed to the inclined surfaces of said roof; and

(iii) a solvent conduit reciprocating carriage supporting said conduit and nozzles for longitudinal reciprocation, so as to dispense solvent onto said roof in over-lapping flow.

5. A baflle structure as in claim 4, including:

(F) An air cylinder engaging said solvent conduit reciprocating carriage as a reciprocating mechanism.

6. A baffle structure in combination with a roof-wet ting solvent dispenser as in claim 4, including:

(G) a source of laminar-flow air positioned in the front end of said chamber opposite said wet Wall baflles, so as to direct laminar-flow air longitudinally through said chamber and against said wet wall bafiie.

7. A combined baffle structure and roof wetting solvent dispenser as in claim 6, said chamber having conveyor entry and exit portals intermediate said source of laminar flow air and said wet-wall baflle and including:

(i) pressurized air-knife means traversing said entry and exit portals.

8. A combined bafile structure and roof wetting dispenser as in claim 6, said reservoir having a collecting roof supported beneath said conveyor, so as to collect without splashing solvent, over spray and bounce back prior to reciprocation.

5 6 9. A baflie structure as in claim 3, said extensions of 2,217,345 10/1940 McGraw 981 15 X said solvent circulation and conduit being pivotable in a 2,694,466 11/1954 Bingman 118326 X horizontal axis, so as to facilitate adjustment of said 2,848,353 8/1958 Norris 118-326 X nozzles from above. 3,123,455 3/1964 Paasche 55--241 X References Cited 5 JOHN P. MCINTOSH, Primary Examiner UNITED STATES PATENTS 1,751,999 3/1930 Hines 55-241 118-326 US. Cl. X.R.

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