GB2119705A - Method for press laminating dry film photo resist - Google Patents

Abstract

A method for press laminating a dry film photo resist onto a workpiece is comprised of the steps of adhering a resist film to the working face of a workpiece, disposing a pressing blank over the resist film to form a sandwich of same between the workpiece and the blank, and press laminating the resist film to the workpiece by application of a laminating-effective pressure to the sandwich at a laminating-effective temperature. The press laminating step is preferably conducted in two stages, comprising the step of hot press laminating the sandwich at an elevated temperature and pressure sufficient to cause localized, uniform flow of the resist film across the working face followed by a cold press laminating step to set and bond the resist film. Shim members are preferably included within the sandwich when raised elements comprise a portion of the working face to maintain a uniformity of separation across the sandwich during the press laminating procedure.

Description

SPECIFICATION Method for press laminating dry film photo resist The present invention relates, generally, to methods for fabricating dies by chemical milling procedures and, more especially, to methods for press laminating a dry film photo resist onto a workpiece in advance of a chemical milling operation to form a die.

Chemical milling of a metal block to form a die has become a popular method for fabricating these articles. Various techniques for chemical milling metallic workpieces, such as steel, to form stamping dies useful in the production of circuit boards are disclosed in the present inventor's U.S.

Patents No. 3,758,350, No. 4,053,348, and No.

4,102,735. Briefly stated, the dies described in those patents include certain configurations which comprise raised die elements in the form of knife edges which are capable of stamping thin metal foil and adhering same to an underlying substrate for the fabrication of a circuit board.

In general, the process disclosed in the aforementioned patents, and which is otherwise used to form conceptually similar die members, is a chemical milling process where a metallic workpiece is repetitively etched in a desired pattern to yield raised die elements separated by recessed die cavities. Portions of the workpiece are protected during the etching process leaving exposed areas for active etching and removal of material. Protection for the selected areas of the die which will form the raised die elements is achieved by the application of an etchant-resistant film to the working face in the desired pattern.

The etchant-resistant film (i.e., "photo resist") applied to a workpiece such as the ones described above is conventionally positioned on the working face of the die by a type of photographic technique. The photo resist material is first applied to the desired portions of the working face of the die block and a pattern having the configuration of the finished die (or one approximating same) is then positioned over the photo resist and the latter is exposed to sensitizing radiation, typically UV light. The resist film is then developed and unexposed portions removed. Those areas corresponding to the retained pattern are imparted with an etchant-resistant film of photo resist whereas those outside the pattern have no such film; yield a die block having etchant-active areas where no resist adheres and etchant-passive areas protected by the resist film.When exposed to an etchant, the active areas are preferentially removed by chemical milling.

In processes for the formation of a knife-edge die by chemical milling a metallic die block, an important goal is the production of cavities adjacent the raised die elements which have good working depth. To achieve these working depths, it is not at all uncommon to etch the die block repetitively in as many as twenty one-minute cycles. Unless the dry film resist is securely and uniformly bonded to the work face of the die block, uneven etching lines and images will result because of etchant undercutting of the die more rapidly or easily in some areas than in others due to a lack of uniformity in the protective film. In turn, this variation in undercut rate will lead to variations in the sidewall slope of the cutting edges and a concomitant lack in the precision of the die thus formed.

The conventional method for bonding a dry film photo resist to a steel workpiece is to adhere the film by means of a heated roller. This is sometimes achieved by using a roll laminating machine or other times by using a hand operated roller. In either event, the objective is to apply sufficient heat and pressure to cause flow of the resist material so that it will fill any irregular pores or marks on the surface of the die block and yield a good, uniform bond thereto. If the die block is cold it may act as a heat sink and retard if not prevent altogether this desirable flow of resist. This will contribute to an unreliable bond between the photo resist and die block whereby the resist film may experience breakdown during and between chemical milling cycles from thermal shock and mechanical stresses due to handling and intermediate cleaning.On the other hand, if the die block is heated it can cause an undesirable outgassing of solvents from the photo resist film which also leads to improper bonding and the same type of unreliable processing during further chemical milling.

The problem of uniform and reliable bonding of a photo resist film to a die block is exacerbated in cases where the die is partially formed and includes raised die elements. It is, at the very least, an extremely tedious chore to achieve a uniform bond through the use of conventional apparatus and methods since the same do not adequately provide compensation for the pressure applied across an ever-changing area of a previously milled plate, with irregular raised surfaces which tend to oppose the heated roller used for application of the resist film. Sometimes, it is impossible to produce an acceptable quality in the resist application without resorting to extensive hand touch-up or other labor-intensive efforts.

Accordingly, the need exists to provide an improved method for the reliable bonding of a resist film to the working face of a die block, and particularly a metallic die block which is to be subjected to a chemical milling procedure.

The present invention advantageously provides a highly reliable method for the application of a dry film photo resist to the working face of a die block where uniform adherence is achieved in a simple yet efficient manner. The method of the present invention may advantageously be employed to apply a dry film photo resist to a die block, whether the same has a generally uniform surface or has been previously imparted with die elements or die element precursors with a raised profile in the working face of the die block.

It has been determined4hat the foregoing advantages may be realized by employing a method for press laminating a dry film photo resist onto a workpiece comprising the steps of adhering a resist film on the working face of the workpiece, disposing a pressing blank over the resist film to form a sandwich of same between the workpiece and the blank, and then press laminating the resist film to the workpiece by application of a laminating-effective pressure to the sandwich at a laminating-effective temperature. The press laminating step is preferably conducted in two stages comprised of an initial hot pressing of the sandwich at an elevated temperature and pressure sufficient to cause localized, uniform flow of the resist film across at least selected areas of the working face followed by a cold pressing of the sandwich to set and bond the resist film.In situations where the working face includes raised elements, portions of the adhered photo resist film are selectively removed to form apertures over portions of the raised die elements and shims are disposed within the apertures prior to the formation of the sandwich. It is also preferred to bed the sandwich to account for out-of-flatness of the press platens to guard against excessive resist flow on one side of the die which would contribute to a lack of uniformity in thickness of the film.

Other advantages of the present invention will become apparent to those skilled in the art, and a fuller understanding achieved, by reference to the following detailed description of the invention, taken in conjunction with the figures of drawing, wherein: Figures iA-1D are diagrammatic representations of a die at various stages of chemmilling; Figure 2 is an isometric view, with parts broken away, showing an assembly for use in press laminating a dry film photo resist onto a workpiece; Figure 3 is a sectional view taken substantially along the line 3-3 of Figure 2; Figure 4 is an isometric view of a die in a preliminary stage of fabrication, where the die has raised die elements shown with a dry film photo resist sheet adhered thereto;; Figure 5 is an isometric view of a portion of an assembly useful in press laminating a dry film photo resist onto the workpiece shown in Figure 4; and Figure 6 is a sectional view taken substantially along the line 6-6 of Figure 5.

The present invention relates, generally, to methods for forming a die from a metal workpiece and, more especially, to methods for press laminating a dry film photo resist onto the workpiece in preparation for a conventional chemical milling thereof. Accordingly, the invention will now be described with reference to certain preferred embodiments within the aforementioned context; although, those skilled in the art will aprreciate that such a description is meant to be exemplary and not limitative.

Heretofore the application of a dry film photo resist to a metallic workpiece has been achieved by a roll lamination technique. Typically, a composite film having a first layer of a dry film resist and a second layer of a polyester protective covering is laid over the working face of a workpiece or die block and the resist film adhered thereto by application of heat and pressure through a roller. Generally, either a roll laminating machine or a hand-operated roller is employed for this purpose. Unacceptable results are oftentimes encountered due to the inability of the roll laminating technique to achieve a uniform and reliable bond between the resist film and underlying metal substrate.

In one aspect of the present invention, the problems attendant the bonding of a resist film to a metal die block are overcome by following an initial bonding procedure by a press laminating or bonding procedure. The initial procedure need only insure a preliminary adherence of the resist film sufficient to yield a "bubble-free" application of the film with a bond which will withstand moderate, subsequent handling. A standard roll laminating procedure is most preferred for this purpose; but others capable of achieving these results might equally well be employed. The subsequent pressing operation is performed by application of a laminating-effective pressure at a laminating-effective temperature. This results in a good degree of flow of the dry film resist so that it fills any irregular pores or marks on the surface and a better, more reliable bond is achieved thereby.Furthermore, the improved adhesion of the resist film to the die block minimizes localized breakdown of the photo resist during and between chem-milling cycles which might result from thermal shock and mechanical stress during handling and cleaning.

Turning to the figures of drawing, in all of which like parts are identified with like reference numerals, Figures lA-i D diagrammatically depict a die blank designated generally as 1 having a top or working face 2 to which is adhered a dry film resist 3 in a pattern leaving an etchantactive area 4. These figures illustrate in general a problem which can occur in the etching of a cavity, designated generally as 5, within the die block 1 when the resist film 3 is not adhered properly to the working face 2.

Let it be assumed that the photo resist film 3 has been applied to the working face 2 by means of a conventional roll laminating technique. Let it further be assumed that a small defect, identified generally as 6, occurred in the bonding of the film 3 to the working face. Such a defect might be, for example, a slight air bubble trapped at the interface between the film 3 and the face 2, a slight pore in the face 2 which was not adequately filled by the resist film 3 during application, or another similar imperfection in the bond between the film and the metal substrate. After the film 3 has been roll laminated onto the die blank, sensitizing radiation for the film is caused to pass through an overlay in the pattern of desired die elements so that regions corresponding to area 4 are not sensitized and, accordingly, remain undeveloped in the subsequent processing of the film. Thus, the film 3 will be retained only in areas on die blank 1 outside the etching pattern.

When the die blank is then exposed to an etchant therefor, typically a ferric chloride solution in a bath maintained at about 1O00F., the etchant active areas such as 4 will be preferentially removed by chemical milling. In turn, the cavity 5 will begin to develop. As it does so, there will be an undercutting of the film 3, indicated generally at 7, as the etchant is able to remove material from both the depth projection of the cavity 5 and its sidewalls.

The dry film resists typically used for establishing the surface patterns on a metal die block are relatively thin, on the order of about 0.002", and are heat sensitive, a characteristic required in order to achieve the bonding lamination of the film to the die blank. These required characteristics pose some problems in etching in, e.g., a ferric chloride bath at about 1 000F. For example, the film will tend to soften slightly and can flex in the undercut region 7, as shown generally in phantom lines in Figure 1 C.

This generally results in a slight rounding of the cavity edge, as shown generally at 8. This occurs even when the film 3 is properly bonded to the die 1. It is an occurrence which can be accounted for in subsequent processing and which, because expected, can be designed around in the initial stages of fabrication. However, where a void or imperfection 6 occurs proximate the edge 8, or where the film is otherwise imperfectly bonded in that region irrespective of the presence of such a defect, ragged edges or other undesirable surface profiles arise, such as the one identified generally as 9 in Figure 1 D.

More specifically, where the film 3 has a good bond to the face 2 at a location proximate the undercut 7, the rounding of the edge 8 will be generally uniform and have a radius on the order of about 0.001-0.002". This rounding of the edge 7 can be removed uniformly to yield a sharp edge by, e.g., uniform surface grinding of the entire workface 2. But, in those locations where a defect 6 is present proximate the rounded edge 8, a ragged chem milling nick or edge 9 will result since the film 3 is not bonded uniformly at the juncture of the face 2 and the cavity 5. These imperfections, as noted above, can arise in a number of different ways and, regardless of the precise nature, these defects have a uniform consequence - the undesirable ragged edge or profile at 9.These defects can be eliminated in large measure by insuring a very good bond of the film 3 to the die face 2 such that there are no air bubbles or slight voids preventing contact between the film and the metal substrate, or by insuring that the application of the film 3 is done so that the film undergoes slight localized and deformable flow which, in turn, provides a good bond.

Figures 2 and 3 illustrate an assembly, designated generally as 10, useful for a press lamination of a dry film photo resist onto the surface of a metal die block in order to provide better adhesion of the film and thereby overcome the aforementioned problems. A steel die blank 12, which may be a low carbon steel or an oil or air hardening tool steel, is first prepared by a surface grinding procedure to yield a smooth, flat work face 14. The flat die blank 12 may be one which has no image etched into its work face 14, one which has a target etch formed therein to a depth of less than about 0.0002" or one where cavities are filled with epoxy to eliminate surface relief. In any of these events, the work face 14 may be considered essentially smooth and have no substantial portion with raised die elements projecting from the surface.

The work face 14 is prepared for receipt of a conventional photo resist film 16 which has a thin, dry film photo resist borne upon a polyester film backing. For this purpose, the blank 12 is first thoroughly cleaned and dried. Preferably, the blank is scrubbed with pumice and water until a "water-breakfree" surface is obtained. The cleaned blank is then rinsed with water at about ambient temperature (e.g., 700F.) and air dried in a manner to avoid oxidation of the cleaned surface. The die is then held at an elevated temperature sufficient to remove residual moisture from the metal pores, holes, and, in the case of a die having filled cavity areas such as, e.g., cavities filled with epoxy, to drive moisture from the interface between the epoxy and the steel.Preferably, the die is heated at about 2250F. + 50F. for about five minutes to achieve these results. Once dried, the die is cooled to approximately 750F. + 50F. for receipt of the photo resist film 16.

Insofar as most photo resist films are whitelight sensitive, the film 16 is applied to the working face 14 using yellow "safe lights" as is conventional in most photographic dark room procedures. The film 16 is preferably adhered to the working face 14 by a conventional roll lamination procedure, and is accomplished to insure that no air pockets are visible between the resist film and the die blank surface(s). The roll lamination may be achieved by using a standard heated roll laminator or, optionally, a heated, hand-held rubber roller. The die blank 12 with the adhered photo resist film 1 6 is then prepared for a press lamination procedure in a hydraulic press having both hot and cold openings.

For each of handling, the die blank 12 is preferably placed on a steel tray 18 having a bottom wall or pan 20, an upstanding front wall 22 and a handle 24. To account for the possibility that the press platens may not be perfectly flat and uniform, the die blank 12 is preferably bedded on the pan 20. For this purpose, rag quality paper 26 is first secured to the bottom wall or pan area 20 of the tray 1 8. Normally, from about 0.01 5" to about 0.020" of paper thickness will be adequate for bedding purposes. The paper may be secured to the pan in any convenient way, such as by means of tape 28 located about the periphery of the bedding. The die with adhered photo resist film is centered on the bedding 26 with the film side up, and the die itself is preferably secured in place on the bedding by adhesive strips 30.

A hardened steel plate 32, prepared with a fine surface-ground finish, is positioned ground-face down on top of the die blank 12 over the film 1 6 to function as a pressing block. Preferably, the length and width dimensions of plate 32 correspond to those of the die blank 12. In order to maintain the plate 32 in position, it is preferably secured to the pan 20 by means of adhesive strips or tape 34. The plate 32 is also bedded with rag quality paper 36, from about 0.01 5" to about 0.020" normally being adequate, which is retained in place by adhesive strips or tape 37. As with bedding 26, the purpose of bedding 36 is to accommodate any out-of-flatness of the press platens. A cover plate 38 is placed over the bedding 36 and is secured to the upstanding front wall of tray 1 8 by adhesive strips 40.All of the steps in assembling this sandwich of components, designated generally as 42, are performed under safeguarded, darkroom conditions to prevent exposure of the photo resist film 1 6 to white light.

However, once the sandwich 42 has been assembled, the photo sensitive film will be adequately protected from inadvertent exposure by the arrangement of parts in the sandwich.

With the sandwich 42 assembled in place on tray 18, the tray is transferred to a hydraulic press having both hot and cold openings. The tray is initially placed within the hot opening of the hydraulic press and the press pressure advanced and maintained. The objective of this step is to cause uniform, localized flow of the dry film resist layer so that it will fill any irregular pores or marks on the work face 14 and achieve intimate contact therewith. Accordingly, the pressure applied should be a laminating-effective pressure while the heated opening in the press is maintained at a laminating-effective temperature.

Placing quantitative limitations on the ranges for effective laminating temperatures and pressures is somewhat problematic insofar as the same are interrelated and both, in turn, related to the resist film employed. Qualitatively, the objective of the hot press laminating step is to provide the desired flow noted above. For some film compositions, the film will become tacky at temperatures only slightly above room temperature, undergo viscous flow at temperatures ranging up to about 125--1500, and tend to become less viscous (almost runny) at temperatures ranging as high as about 1 75-2000F. Depending upon the state of viscosity, higher or lower laminating pressures will be necessary or desirable.Normally, the pressuretemperature relationship is one of inverse proportionality; in the sense that the less viscous the film, as a consequence of a higher temperature, the less pressure need be applied.

Thus, the temperature range of interest is one bounded at the low end where the temperature is sufficient to provide slightly viscous flow and bounded at the upper end by one less than that where viscosity becomes so low that the application of pressure merely squeezes the resist film outwardly of the die block without the ability to control that flow characteristic. Generally, a temperature in the range of from about 100 to about 1750 F. will be suitable; more preferably one in the range of from about 110 to about 135 F. in order to achieve somewhat better control over the flow; and most preferably one from about 11 5 to about 1250 F. to provide an optimum or nearly optimum ability to control resist film flow.When dealing with the flat work faces, a pressure application in the general range of from about 500 psig to about 1500 psig will be satisfactory; preferably one from about 750 psig to about 1250 psig; and most preferably a pressure at about 1000 psig, all of which pressures are calculated based upon the surface area of the workpiece. The sandwich should remain within the heated press opening under these laminatingeffective pressure and temperature conditions normally from about 4 to about 5 minutes, but this too will vary from film to film depending on the characteristics imparted by the film manufacturer.

Following the initial hot press laminating step, the sandwich 42 is subjected to a cold press laminating step to set the pliant film and bond it to the work face 14. For this step, the sandwich 42 borner on tray 18 is removed from the hot opening in the press and transferred to a cold opening therein. The pressure and temperature conditions in the cold opening of the press are again selected to effectuate the desired qualitative goal setting and bonding the pliant film. The temperature of the cold opening in the press is normally established by water cooling where the water is typically tap water.Accordingly, depending upon the ambient, this temperature may range anywhere from about 500 F. to about 700 F., but will preferably be about 600 F. The pressure, however, is selected to be within the same general range as that for the hot press laminating step. Thus, pressures in the range of from about 500 psig to about 1500 psig, preferably from about 750 psig to 1250 psig, and most preferably 1000 psig, based on the surface area of the flat work face 14, will be employed.

This cold press laminating step is conducted for a time sufficient to set and bond the film; usually from about 4 to about 6 minutes being sufficient, nominally about 5 minutes under most conditions. The duration of this cold press laminating step is somewhat a function of the temperature of the cold opening in the press as well as the parameters established during the hot press laminating. Accordingly, some minor adjustment may be found necessary or desirable; which adjustment is certainly within the skill of the art.

After the cold pressing step, the tray is removed from the press to a place where dark room conditions are established and the sandwich is separated to yield a die blank having the dry film photo resist uniformly bonded thereto with good bond integrity. The blank can then be processed as normal, by exposing the resist to sensitizing radiation in a desired pattern to provide etchant active and etchant-passive regions and then selectively etching the blank. Because of the improved bonding of the resist to the workpiece, improved results will be realized during the subsequent chem-milling operations.

Example 1 is given below to illustrate the manner in which a dry film photo resist is press laminated to a flat die blank in accordance with the foregoing procedure.

EXAMPLE 1 A steel die blank is first prepared by surface grinding same to a flat finish of about 16 microinches. The die blank is cleaned by scrubbing it with pumice and water until a "waterbreakfree" surface is obtained, is rinsed with water at approximately 700 F., and is then immediately air dried to avoid oxidation of the steel surface.

The cleaned die is transferred to a warming furnace maintained at about 2250 F. + 50F. for about 5 minutes to insure the die is moisture free.

It is then cooled to about 750 F. and transferred to a space having dark room conditions.

A piece of dry film photo resist, known as type GT made by the Thiokol Dynachem Corp., is prepared for adherence to the die blank. This dry film photo resist is one which has a resist film thickness of approximately 0.002" and a polyester film backing with a thickness of approximately 0.001". This photo resist is white-light sensitive and, accordingly, it is handled using yellow safety lights. The film is adhered to the prepared working face of the die blank by means of a standard heated roll laminator and the adhered film is inspected to insure that no air pockets are visible between the resist film and the die blank surface.

A steel press tray is provided with about 0.017" of rag quality paper as bedding, this paper being secured to the pan of the tray by masking tape.

The prepared die blank with adhered photo resist film is centered on the bedding and is itself secured to the pan by masking tape. A 1/2" thick steel plate which has been hardened and surface ground to a fine finish is placed finish side down on the film and is secured in position by masking tape. About 0.01 7" of rag quality paper is provided as bedding on top of the pressing blank, to which it is secured by masking tape. Lastly a steel plate about 1/1 6n thick is placed over the bedding and this plate is secured to the upstanding front wall of the tray by masking tape to complete the sandwich. At this time, the photo resist layer is adequately protected from inadvertent sensitization by white light, and the tray may safely be removed from the dark room.

The tray is transferred to the hot opening of a hydraulic press, which is maintained at a temperature of about 1 200 F. + 50F.The press pressure is advanced to 1000 psig based upon the total surface area of the die blank. This laminatingeffective pressure and the laminating-effective temperature are maintained for approximately 4.5 minutes; whereupon press pressure is relieved and the tray placed in the cold opening of the press through which is circulating tap water having a temperature of about 60#650 F. The press pressure is advanced to about 1000 psig based upon the total surface area of the die blank and this is maintained for about 5 minutes.

Following the cold pressing, the tray is removed to a space having dark room conditions and the sandwich is separated. At this point, the photo resist film loses the protection afforded by the other components in the sandwich and must be handled to avoid inadvertent exposure.

The die blank is then processed according to the photo resist exposure and chem-milling techniques set forth in the present inventor's U.S.

Patents No. 3,758,350, No. 4,053,348 and No.

4,102,735. After the chem-milling process is completed, it is determined that there are no unacceptable variations in undercutting rate at or near the edges of the retained photo resist, indicative of a good and uniform bond between the photo resist and the metal substrate.

The foregoing description concerns a method for press laminating a photo resist film to a substantially flat work face of the die blank 12.

Where the work face includes raised die elements in the blank, some unique problems are presented.

Figures 4-6 illustrate a die blank 12 like the one described above, save for the fact that the working surface 14 includes a plurality of raised die elements 44 formed therein.

The basic procedure outlined above for press laminating the resist film 1 6 to the flat work face 14 is followed with but minor deviation as respects the embodiment of Figures 4-6. After the resist film 16 is roll laminated to a prepared die blank 12, a series of apertures 46, one of which is shown in detail in Figure 6, is formed through the film 16 at selected positions on the raised die elements 44 as best viewed in Figure 4.

Each of the apertures is preferably a rectilinear aperture, and most preferably a square aperture, pierced through the entire film 16. Within each aperture 46 is disposed a stabilizer shim 48, as best viewed in Figures 5 and 6. The stabilizer shims are preferably formed from hardened steel and are preferably dimensioned to have a length and width slightly less than the length and width dimensions of the mating apertures 46. The shims are ground to have a thickness approximately equal to or only slightly less than the combined thickness of the dry film resist and backing layer of the sheet 16, as best viewed in Figure 6.In that figure, the film 16 is represented to be comprised of a dry film resist layer having a typical thickness of about 0.002" and an upper protective layer having a typical thickness of about 0.001"; thwerefore, the thickness of stabilizer shim 48 would preferably be about 0.003" (+0.0001, -0.0005).

The configuration shown in Figure 5 illustrating the placement of the shims and apertures in this embodiment is a rather idealized one since a typical die will have quite a number of raised elements 44 spaced across the upper working surface thereof. As the fundamental purpose for the shims is to prevent a rocking motion of the pressing blank on these raised elements, it is preferable to position the shims generally symmetrically about the die block including, if need be, some near the central portion thereof to guard against a bowing of the pressing blank.

Since the raised elements will generally always have a lateral dimension of at least 0.010" and typically at least about 0.020", it is relatively easy to position the individual shims within a central portion on each raised die element. That portion will subsequently undergo a chemical milling procedure in accordance with the processes set forth in one or more of the present inventor's U.S.

Patents No. 3,758,350, No. 4,053,348, and No.

4,102,735, and will therefore be provided with cavities or recesses in the raised elements.

Accordingly, while it is preferred to strive for a centering position of each shim vis-a-vis each die element bearing such a shim, that is not crucial; albeit, one is well advised to keep the shim from the edge region of these die elements for optimum results.

The stabilizer shims 48 are maintained in place by a polymeric cover film 50 preferably disposed over the entire upper surface or working face of the die blank 12. Most preferably, the film 50 is a polyester film of about 0.002" which is secured along the edges of the die blank 12 by adhesive strips 52 such as masking tape. The die blank with shims captured within the apertures 46 by the protective sheet 50 is then placed upon the pan of the tray 18 over bedding 26. A sandwich is then made in the same manner as aforesaid by including a pressing blank over the film 50, itself covered with bedding and an upper plate. This sandwich borne upon the steel tray may then be disposed sequentially in the hot and cold openings of a press.

In this situation, the laminating-effective temperature is within approximately the same preferred ranges set forth above, however the press pressure is reduced to account for the fact that the application of pressure is now made only across the raised elements. Preferably, the press pressure will be maintained within a range of from about 350 to about 750 psig based upon the surface area of the raised die blank elements, and most preferably at about 500 psig. Otherwise, the procedure continues as aforesaid to yield a wellbonded resist layer 16. Once the pressing procedure is over, the sandwich is separated under dark room conditions and the shim openings inspected to ascertain that the dry film resist achieved sufficient bonding viscosity to observe some slight flow of resist around the shim.After the photo resist is exposed and developed, the areas beneath the shims can be touched up by hand to provide a resist surface at those locations and the die blank may then be processed in accordance with the chemical milling procedures set forth in the present inventor s aforesaid patents.

In order to illustrate the manner in which a photo resist film is press laminated to a raised relief die blank, the following example is given.

EXAMPLE 2 A steel die blank with raised relief die elements formed in a previous fabrication procedure is first cleaned by scrubbing same with pumice and water until a water break-free surface is obtained.

The blank is rinsed with water at approximately 700 F. and air dried rapidly to avoid oxidation of the working face. The cleaned die is then heated in a warming furnace maintained at about 225 " F. + 50F. for about 5 minutes to remove residual moisture. Thereupon, the die is cooled to about 750F. and is ready for receipt of a photo resist film.

The same type GT film used in Example 1 is prepared as is conventional for roll lamination to the working face of the die blank. This film is comprised of a dry film resist of approximately 0.002" backed by polyester film of approximately 0.001". The film is disposed over the working face of the die and roll laminated using a standard heated roll laminator. The laminated film is then inspected to insure that there are no visible air pockets between the resist film and the raised die blank surfaces.

Small openings of approximately 0.050" square are cut through the resist film to expose the upper metallic surface of the raised die elements in a pattern like that shown in Figure 4. The square apertures are disposed as symmetrically as possible to prevent any rocking of the sandwich to be prepared when it is placed within the press.

Shims made from hardened steel about 0.003" thick (corresponding to the combined thickness of layers in the resist film) and about 0.040" square are then disposed within each of the apertures. A sheet of polyester film approximately 0.002" is then laid on top of the working face, covering the stabilizer shims, and this is secured by masking tape to the edges of the die blank.

About 0.017" of rag quality paper is secured as bedding medium on the pan of a steel tray, secured in place by masking tape as shown in Figure 5. The die blank covered with the upper polyester film is then centered on the bedding paper and secured in place by masking tape. A 1/2" thick steel plate, hardened and surface ground to a fine finish, is placed finish side down on the upper polyester protective film and is secured to the pan by masking tape. The upper face of the steel plate is covered with about 0.017" of a rag quality paper bedding which is secured by masking tape and itself covered by a metal cover sheet to form a sandwich.

The sandwich is placed within the heated opening of a hydraulic press which is maintained at about 1200 F. + 50F. and the press pressure is advanced to 500 psig based upon the surface area of the raised die elements. This laminatingeffective pressure is maintained at the laminatingeffective temperature for about 4.5 minutes. The pressure is relieved and the tray is then transferred to the cold opening of the press having cooling water at about 650 F. circulating therein and the pressure is advanced again to 500 psig based upon the surface area of the raised die elements.

This pressure is held for 5 minutes, the pressure is relieved, and the tray removed to a space having dark room conditions. The sandwich is separated, the shims removed and the openings inspected for sufficient flow of resist. The die blank is then processed in accordance with the present inventor's photo resist/chemical milling techniques noted above. Those areas corresponding to the placement of the shims may be provided with a layer of resist applied, e.g.; by a hand touch-up using a brush.

Upon further processing, it is determined that the photo resist film is bonded uniformly and securely to the raised die elements as indicated by the fact that there are no substantial variations in the undercut rate during subsequent etching.

The same techniques described above can be employed to good advantage for securing a photo resist film to most any metallic die block.

Accordingly, those skilled in the art will appreciate that various changes, substitutions, omissions, and modifications may be made without departing from the spirit of the present invention. Therefore, it is intended that the scope of the invention be limited solely by that of the claims granted herein.

Claims (29)

1. A method for adhering a dry film photo resist to a workpiece, comprising the step of press laminating said film to the working face of said workpiece.

2. The method of claim 1, wherein said press laminating step is comprised of the steps of: hot press laminating said film at a laminatingeffective pressure and temperature sufficient to cause localized flow of said resist; and, cold press laminating said film at a laminatingeffective pressure to set and bond said resist to said workpiece.

3. A method for press laminating a dry film photo resist to the working face of a metal workpiece, comprising the steps of: adhering a photo resist film to the working face of a metal workpiece; disposing a pressing blank over said film to form a sandwich of same between said blank and said workpiece; and, press laminating said film to said workpiece by application of a laminating-effective pressure to said sandwith at a laminating-effective temperature.

4. The method of claim 3, wherein said presslaminating step is comprised of the steps of: hot press laminating said film at an elevated temperature and pressure sufficient to cause localized flow of said resist; and, cold press laminating said film to set and bond said resist to said working face.

5. The method of claims 3 or 4, further comprising the step of bedding said sandwich prior to said press laminating step(s).

6. The method of claim 5, wherein said workpiece is a flat face die blank, and further wherein said press laminating step is conducted under a pressure in the range of from about 500 psig to about 1500 psig, based on the surface area of said working face.

7. The method of claim 6, wherein said pressure is in the range of from about 750 to about 1250 psig.

8. The method of claim 6, wherein said pressure is about 1000 psig.

9. The method of claim 6, wherein said press laminating step is conducted initially at a temperature in the range of from about 1O00F. to about 1750F.

10. The method of claim 9, wherein said temperature is in the range of from about 1 lO0F.

to about 1 350F.

11. The method of claim 9, wherein said temperature is about 1 200 F.

12. The method of claim 5, wherein said workpiece is a raised profile die blank including at least one raised die element, said method further comprising the steps of: forming at least one aperture through said dry film photo resist at the location of at least one of said die elements; and, disposing shim means within each aperture, wherein each of said shim means has a thickness approximately equal to the thickness of said dry film photo resist.

13. The method of claim 12, further comprising the step of disposing retaining means over said shim means.

14. The method of claim 13, wherein said retaining means is comprised of a sheet of a flexible film.

1 5. The method of claim 12, wherein said press laminating step is conducted under a pressure in the range of from about 350 psig to about 750 psig, based upon the surface area of said die element(s).

1 6. The method of claim 15, wherein said pressure is about 500 psig.

17. The method of claim 15, wherein said press laminating step is conducted initially at a temperature in the range of from about 1000F. to about 1 750F.

18. The method of claims 17, wherein said temperature is in the range of about 11 00F. to about 135 F.

19. The method of claim 17, wherein said temperature is about 1 200 F.

20. A method for press laminating a dry film photo resist to the working face of a flat die blank, comprising the steps of: roll laminating a dry film photo resist onto a cleaned and conditioned working face of flat die blank; bedding the bottom side of said die blank on a press pan; disposing a pressing blank over said dry film photo resist to form a sandwich of said film between said press blank and said die blank; bedding the top side of said press blank; disposing a pressing cover over the bedding on said press blank to yield a press sandwich; hot pressing said press sandwich in a heated press jaw at a pressure in the range of from about 500 psig to about 1500 psig based on the surface area of said working face and at a temperature in the range of from about 1000F. to about 1750F.

for a time sufficient to permit localized flow of said resist; and, cold pressing said press sandwich in cold press jaws at a pressure in the range of from about 500 psig to about 1500 psig based on the area of said working face for a time sufficient to permit said resist to set and bond to said working face.

21.The method of claim 20, wherein: said hot pressing step is conducted under a pressure of about 1000 psig and at a temperature of about 1200 F. for from about 4 to about 5 minutes; and, said cold pressing step is conducted under a pressure of about 1000 psig for from about 4 to about 6 minutes.

22. A method for press laminating a dry film photo resist to the working face of a raised relief die blank having at least one raised die element, comprising the steps of: roll laminating a dry film photo resist to the working face(s) of the raised die element(s) of a raised relief die blank; forming at least one aperture through said dry film photo resist; disposing shim means in each aperture, said shim means having a thickness approximately equal to that of said dry film photo resist; disposing a protective cover sheet over said die blank to capture each of said shim means within its respective aperture; bedding the bottom side of said die blank on a press pan; disposing a pressing blank over said protective cover sheet to form a sandwich of said sheet and said film between said pressing blank and said die blank, bedding the top side of said press blank;; disposing a pressing cover over the bedding on said press blank to yield a press sandwich; hot pressing said press sandwich in a heated press jaw at a pressure in the range of from about 350 psig to about 750 psig based on the surface area of said die element(s) and at a temperature in the range of from about 1000F. to about 1750F.

for a time sufficient to permit localized flow of said resist; and, cold pressing said press sandwich in cold press jaws at a pressure in the range of from about 350 psig to about 750 psig based on the area of said die element(s) for a time sufficient to permit said resist to set and bond to the working face thereof.

23. The method of claim 22, wherein: said hot pressing step is conducted under a pressure of about 500 psig and at a temperature of about 1 200F. for from about 4 to about 5 minutes; and, said cold pressing step is conducted under a pressure of about 500 psig for from about 4 to about 6 minutes.

24. The method of claim 5, wherein from about 0.015" to about 0.020" of rag quality paper is employed as a bedding medium.

25. The method of claim 20, wherein from about 0.01 5" to about 0.020" of rag quality paper is employed as a bedding medium.

26. The method of claim 22, wherein from about 0.015" to about 0.020" of rag quality paper is employed as a bedding medium.

27. The die made in accordance with claims 1, 3,20,or22.

28. The die made in accordance with claim 5.

29. A method for superimposing a dry film photo resist on a workpiece substantially as hereinbefore described with reference to the accompanying drawings.