US 2820131 A
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Description (OCR text may contain errors)
Jan. 14, 1958 G. 'r. KODAMA 2,820,131
CURING OVEN Filed Aug. 1, 1951 GEORGE 'Z' KODAMA INVENTOR.
' ms Arne/gr United States Patent CURING OVEN George T. Kodama, Nashua, N. H., assignor to Sprague Electric Company, North Adams, Mass., a corporation of Massachusetts Application August 1, 1951, Serial No. 239,810
2 Claims. (Cl. 219-34) This invention relates to new and improved apparatus and methods for curing ceramic bodies which have been printed with electrically conductive layers on their surfaces.
A great deal of work has gone into printed circuit elements for use in various electrical devices. Unfortunately the printed resistance elements produced by known methods, such as are indicated in the various Bureau of Standards publications on the subject, have the defect that the resistance values of the various layers printed upon a ceramic body are very unpredictable. Printed elements will vary as much as in resistance values when seemingly very small and insignificant factors varied during their production. One of the prime factors which has influenced this tendency of printed resistance layers to change in value has been the curing of the resistance ink after it has been dried on a ceramic body.
The problems encountered in curing of resistance inks become extremely troublesome when it is desired to obtain on a ceramic plate a number of printed resistance elements having different resistance values for a given size. According to the present methods, this can be accomplished only by the use of different value separate inks which are screened separately and dried separately, and finally all cured together. It has been almost impossible to obtain different printed resistance layers of predictable values on a ceramic matrix, using this method.
An object of this invention is to overcome the aforegoing difficulties. A further object of this invention is to provide a method by which a number of different predictable resistance elements may be simultaneously printed or screened on an inert matrix and then cured simultaneously. Further objects of this invention will be apparent from this specification and the appended claims.
These objects are obtained by virtue of the use of a continuous curing oven in which the precise amount and type of heat applied to any printed circuit element may be accurately controlled. The invention will best be understood with reference to the appended drawings, in which Fig. 1 shows a top view of an oven in accordance with this invention;
Fig. 2 shows a sectional view of this oven taken along line 2-2 in Fig. 1;
Fig. 3 shows a similar sectional view taken along line 3-3 in Fig. l; and
Pig. 4 shows a sectional view of the conveyor belt system taken along line 44 in Fig. 3.
In all of these figures, like numerals designate like parts.
As is in Figs. 1 and 2 the oven 10 is crossed by a belt 11 running between external pulleys 12 and 13, and powered by the unit 14. The oven body itself consists of side Walls 16 and 17, and top and bottom walls 18 and 19 as well as end walls. Vents 21 and 22 are located at the opposed ends of the oven 10 and are provided with the dampers 23 and 24, in order to control the degree and type of heat within the oven, as will be explained.
The actual heating is preferably performed by means of the infra red lamps 26, 27 and 28, suspended from the top 18 of the oven by means of adjustable supports 31, 32 and 33 extending through the bearing blocks 37, 38 and 39. These lamps may be moved up or down so as to provide greater or lesser degrees of radiation upon the belt 11 by means of any of the knobs 34, 35 or 36. The actual degree of heat in any spot may be also regulated by the positions of the shade elements 40 projecting into the oven proper through the walls 16 and 17 and the bearing blocks 42 and 43. The exact positions of the elements 40 over the belt 11 may be regulated by sliding their handles 45 through these bearing blocks.
An appropriate loading chute 48 is shown at the entrance end to the oven 10 directly above the pulley 13, and is provided with guides 49 to insure the precise placement of the ceramic elements upon the belt as they are passed through the oven 10. At the discharge pulley 12, a suitable chute 50 is provided for the removal of these elements. It is to be understood that these ceramic plates may be positioned or removed in any manner, either by hand or machine.
During the operation of the device, small ceramic plates which have been printed with a suitable resistance ink and then dried, may be precisely positioned on the belt 11 by means of the chute 48 and guides 49. Their positioning is such that during their progress through the oven 10 on the belt 11 they may or may not be covered by a line, or part of a line, of shade elements 40, and, hence, may be cured to various desired degrees. During their passage through the oven, these ceramic elements first pass through the preheating zone 52 in order to gradually bring them up to curing conditions and to avoid breakage. This zone 52 may also be used to dry freshly printed elements.
The lamps 26, 27 and 28, are preferably of the infrared type in order to cure the resin by radiation. However, if desired, these lamps may be used in conjunction with other heating means such as hot air. By proper adjustment of the dampers 23 and 24 it is possible to use the device as a conventional oven, or as an oven with partial infra-red heating, or as an infra-red oven. When it is desired to cure printed elements on both sides of the ceramic matrix, the belt 11 may be formed of an appropriate metal chain, and infra-red illumination may be applied from the under side of this belt.
In some cases it is desirable to use ultra-violet radiation instead of the infra-red as indicated above, in order to promote resin polymerization and other reactions.
The shade elements 40 can be made in any variety of manners in order to obtain special effects. They may be made cup shaped, or merely fiat shaped; they may be formed with a shiny upper surface so as to reflect heat radiations, or they may be formed with a black upper surface in order to concentrate the heat. Of course, any element 4t may be made Wider than any other element in order to cover more than one specified area of the belt. Those skilled in the art will realize that these members 4-6 need not be attached to the oven in the precise manner indicated, but may be positioned in any manner so long as they achieve the desired effect. When radiation is needed beneath the belt 11 they may, of course, also be used beneath this belt.
The exact time which any printed matrix must be cured will vary with a number of factors besides the kind and intensity of heat applied to it. With the apparatus forming this invention, the time required for the curing cycle can be conveniently controlled. For most applications 10 minutes curing at an approximate temperature of 500 to. 600 F. using any of the standard types of resistance links developed by the Bureau of Standards, is satisfactory. Of course, a great deal of leeway is allowed. In general, the shorter the curing time the much higher the resistance value obtained. It is to be emphasized that the relationship between the curing time and the resistance value is not purely linear.
The apparatus and process set forth herein is primarily intended for usage with resistance inks which have been screened upon one side ceramic matrices. However, it is to be emphasized. that the invention is broader than this specific application. For example, capacitance layers which have been applied to both sides of a ceramic base can be cured in accordance with this invention, or both silverand resistance films can be simultaneously cured. Other base materials such as glass can be used to support printed elements. By appropriate alteration of the com ditions duringthe pre-heating portion of the oven 52, it is possible to dispense with the usual drying employed with resistance inks.
A great many modifications of this invention will occur to those versed in the art. For example, a rotating table can be used to replace the moving belt shown. Such modifications are to be considered part of the inventive concept herein employed in so far as they are defined by the appended claims.
What is claimed is:
1. A curing oven for printed circuit components comprising, a housing, a component carrier, driving mechanism connected to move the carrier in a predetermined path through the housing, adjustable heating lamps in the housing directed toward the path in which the components are carried by the carrier, fixed shade bodies adjustably positioned between said lamps and said last named path, said members being narrower than the last named path to vary the radiant heating effects on a portion of the surface of the components as they are baked.
2. The combination of claim 1 in which the housing has vent means that includes damper mechanism controllable to provide a desired amount of oven heating with the lamp heating.
References Cited in the file of this patent UNITED STATES PATENTS 1,526,363 Nitch Feb. 17, 1925 1,623,567 Wappler Apr. 5, 1927 1,880,954 Fahrenwald Oct. 4, 1932 2,204,465 Baler June 11, 1940 2,221,776 Carlson Nov. 19, 1940 2,321,938 Quinn June 15, 1943 2,340,354 Wells Feb. 1, 1944 2,353,165 Kreidl July 11, 1944 2,354,658 Barber Aug. 1, 1944 2,441,960 Eisler May 28, 1946 2,402,631 Hull June 25, 1946 2,558,338 Clements June 26, 1951 2,582,438 Jones Jan. 15, 1952 2,624,013 Marks Dec. 30, 1952 FOREIGN PATENTS 579,946 Great Britain Aug. 21, 1946 OTHER REFERENCES New Advances in Printed Circuits, Natl Bureau of Standards, misc. pub. 192, 1948, page 15.