US3885520A

US3885520A - Vapor deposition apparatus with rotatable ring mask

Info

Publication number: US3885520A
Application number: US449219A
Authority: US
Inventors: John F Krumme
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-03-08
Filing date: 1974-03-08
Publication date: 1975-05-27
Anticipated expiration: 1992-05-27

Abstract

Apparatus for carrying a substrate strip of material through a deposition area of a vacuum deposition system is described. The apparatus includes a rotatable masking wheel defined by a pair of axially aligned and spaced apart masking rims upon which the substrate strip rides bridging the gap therebetween during passage through the deposition area. A plurality of connectors extend between the rims and secure the same together at locations spaced circumferentially of such rims to normally maintain the rims a predetermined spacing apart. A source of the material to be deposited on the strip is positioned inwardly of the rims, whereby material therefrom will be deposited on the area of the strip which is exposed between such rims in view of the fact that such strip bridges the gap therebetween. The coating material will thus form a stripe along the length of the substrate strip with the edges of the masking rims forming the edges of the stripe. Each of the connectors extends between the rims at a location which is spaced inwardly of the location where the strip bridges the gap between the rims, and the source of coating material is positioned inwardly of the wheel at a location which is off its axis of rotation, whereby the portions of the strip area between the rims shielded by the connectors from the deposition of material shifts along the stripe area as the wheel rotates so that all portions of the area of the substrate strip exposed between such rims are at some time exposed to deposited material during passage of the substrate through the deposition area.

Description

United States Patent [1 1 Krumme [45] May 27, 1975 1 1 VAPOR DEPOSITION APPARATUS WITH ROTATABLE RING MASK John F. Krumme, 87 Upenuf Rd., Woodside, Calif. 94062 [22] Filed: Mar. 8, 1974 [21] Appl. No.: 449,219

[76] Inventor:

[56] References Cited UNITED STATES PATENTS 2,816,523 12/1957 Johnson 118/49 X 2,847,325 8/1958 Riseman et a1. 118/49 X 2,948,261 8/1960 McGraw, Jr. I 118/49 3,102,046 8/1963 Bushey 118/301 X 3,205,855 9/1965 Ault 118/49 3,394,679 7/1968 Bentley, Jr 118/49 3,396,696 8/1968 Becker 118/49 3,699,917 10/1972 Deverse et al. 118/49 3,735,728 5/1973 Krumme et a1. 118/49 3,818,982 6/1974 Wagner 118/301 X FOREIGN PATENTS OR APPLICATIONS 760,543 6/1953 Germany 118/49 70,468 12/1969 Germany 118/48 Primary Examiner-Morris Kaplan Attorney, Agent, or FirmC. Michael Zimmerman, Esq.

[57] ABSTRACT Apparatus for carrying a substrate strip of material through a deposition area of a vacuum deposition system is described. The apparatus includes a rotatable masking wheel defined by a pair of axially aligned and spaced apart masking rims upon which the substrate strip rides bridging the gap therebetween during passage through the deposition area. A plurality of connectors extend between the rims and secure the same together at locations spaced circumferentially of such rims to normally maintain the rims a predetermined spacing apart. A source of the material to be deposited on the strip is positioned inwardly of the rims, whereby material therefrom will be deposited on the area of the strip which is exposed between such rims in view of the fact that such strip bridges the gap therebetween. The coating material will thus form a stripe along the length of the substrate strip with the edges of the masking rims forming the edges of the stripe. Each of the connectors extends between the rims at a location which is spaced inwardly of the location where the strip bridges the gap between the rims, and the source of coating material is positioned inwardly of the wheel at a location which is off its axis of rotation, whereby the portions of the strip area between the rims shielded by the connectors from the deposition of material shifts along the'stripe area as the wheel rotates so that all portions of the area of the substrate strip exposed between such rims are at some time exposed to deposited material during passage of the substrate through the deposition area.

7 Claims, 5 Drawing Figures PATENTED MAY 2 71975 SHEET SOURCE VAPOR DEPOSITION APPARATUS WITH ROTATABLE RING MASK BACKGROUND OF THE INVENTION The present invention relates to vacuum deposition and, more particularly, to improved apparatus for carrying an elongated substrate strip of material through a deposition area for deposition of material thereon in a stripe.

Development of vacuum deposition technology, i.e., the application by deposition under vacuum of a thin coating of a material to a substrate, has played an important part in the development of modern technology. For example, the only practical way of producing the thin film coatings necessary in the fabrication of integrated circuits is via vacuum deposition. Not only are integrated circuit chips fabricated by applying thin coatings of various materials to a substrate, but so are the lead frames to which such chips are often electrically and mechanically connected for support. Such lead frames are most often in the form of an elongated strip of an electrically conductive material having a plurality of conducting arms formed by stamping or the like to which the leads from the integrated circuit chips are bonded. During the fabrication of a lead frame, a stripe of a material compatible with the chip leads is deposited along a stripe of the material extending lengthwise. In a completed lead frame, such deposited material forms a coating on the tips of the conducting arms to which the integrated chips are to be bonded.

Typically, the stripe of deposited material is provided on the substrate for the lead frame by passing such substrate through a deposition area while masking that portion of such substrate on which a coating is not desired. US. Pat. No. 3,735,728 of which I am a coinventor, describes and claims a typical arrangement for carrying a lead frame substrate through a deposition area. As discussed therein, the strip of material is unwound from a payoff reel or spindle and is carried by a rotating masking wheel through the deposition area and then again wound onto a take-up reel or spindle. The masking wheel is generally made up of a pair of axially aligned and spaced-apart masking rims upon which the strip rides bridging the gap therebetween during rotation of the wheel. The source of the material to be deposited is positioned inwardly of the rims so that material therefrom will be deposited on the area of the strip exposed between such rims, i.e., that area bridging the gap therebetween. Although the source of material can be of any type utilized to provide a vapor or plasma from which the material will be deposited, it is most often an electron gun evaporation source.

The arrangement disclosed in the above patent is one in which the two spaced apart rims of the masking wheel are independent of one another. That is, such rims are not physically secured together and they are otherwise free to rotate separately. It has been found, however, that while such an arrangement has certain advantages, there are disadvantages which make it less than satisfactory for precision work. For one thing, it is not unusual for differential thermal expansion to cause one of the masking rims to have a slightly greater outer circumference than the other. The result is that the substrate strip will ride on only one rim while passing through the deposition area, and be slightly spaced above the other. The result is that the smaller of the two masking rims will not provide a sharp demarcation between the area on which material is deposited and that which is to be masked. Rather, because of the spacing of the substrate from the smaller masking rim, some depositing material will find its way between the substrate and such masking rim to obviate a sharp line of demarcation.

Another disadvantage of the arrangement described in the patent is that it is impossible, as a practical matter, to maintain the rims parallel at all times during their rotation. The result is that the width of the gap between them varies, with a consequent variation in the width of the stripe of material deposited on the substrate. Moreover, while as mentioned in the patent, apparatuses have been provided in the past in which the masking wheel is not in the form of a pair of separate rims, but rather is provided with apertures exposing portions of the strip for the deposition of material, such apparatuses are limited in that neither continuous stripes of deposited material nor many different masking designs can be provided.

SUMMARY OF THE INVENTION The present invention provides a vacuum deposition apparatus for depositing a material in a stripe on an elongated substrate strip, not having the above disadvantages. In its basic aspects, the apparatus includes a masking wheel, as is usual, for delimiting an area of the substrate strip upon which the material is to be deposited during passage of such strip through a deposition area. The wheel is of the type which includes a pair of axially aligned and spaced apart masking rims upon which the strip rides bridging the gap therebetween during passage through the deposition area. A plurality of connectors extend between the rims and secure the same together at locations spaced circumferentially of such rims to normally maintain the rims a predetermined spacing apart defining the width of the stripe on which material is to be deposited. A source of the coating material is positioned inwardly of the rims whereby material therefrom will be deposited on the area of the strip exposed between such rims.

As a particularly salient feature of the instant invention, each of the connectors extends between the rims at a location spaced inwardly of the location at which the strip bridges the gap between the rims, and the source is positioned inwardly of such rims at a location which is off the axis of rotation thereof. The result is that the strip area portions between the rims shielded by the connectors from the material source shift along such area as the rims rotate. By proper placement of the source relative to the geometry of the masking rims and the connectors, every portion of the strip area exposed between the rims is at sometime exposed to de posited material during passage of the strip through the deposition area. Thus, the provisions of the connectors to rigidly maintain the rims in their spaced apart relationship will not result in either a portion of such area being entirely shielded from the deposited material nor there being any significant variation in the amount of material deposited on the stripe. In this connection, the portion of the stripe shielded at any given time by a connector should be small relative to the length of substrate within the deposition area at such time.

Most desirably, the connectors which secure the masking rims together are each of a heat conductive material and in good thermal contact with the rims.

The connectors will thereby act, in effect, as thermal bridges tending to maintain the rims at the same temperature and prevent differential thermal expansion. Thus, the problem of differential thermal expansion causing the substrate strip to ride on only one of the two rims is substantially avoided.

The invention includes other features and advantages which will become apparent from the following more detailed description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the accompanying two sheets of drawing:

FIG. 1 is an isometric view of a preferred embodiment of the vacuum deposition apparatus of the invention;

FIG. 2 is an enlarged, partial and schematic view illustrating the relationships of various aspects of the preferred embodiment of FIG. 1;

FIG. 3 is a sectional view taken on the plane indicated by the lines 33 in FIG. 1, illustrating details of the construction of the preferred embodiment of FIG.

FIG. 4 is a sectional view similar to FIG. 3 illustrating another preferred embodiment of the invention; and

FIG. 5 is an enlarged, partial and schematic view similar to FIG. 2 of a third preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1, a masking wheel 11 of a preferred embodiment of the invention is illustrated mounted for rotation about its axis by a support structure 12 within a vacuum chamber, the floor of which is indicated at 13.

Masking wheel 11 is made up of a pair of axially aligned and spaced apart

masking rims

14 and 16 which have generally the same outer peripheral circumference. As is illustrated, an elongated substrate stripe 17 upon which a material is to be deposited in, for example, a continuous stripe is passed over the rims and rides on their outer peripheries bridging the gap therebetween. As can best be seen from FIG. 3, each of the rims l4 and 16 is provided with a recess within which the edge of the strip associated therewith rides. It will be seen that the recesses in the two rims cooperate to define a groove or track at the outer periphery of the masking wheel which properly positions the substrate strip over the gap 19 between the rims.

Although not illustrated, the apparatus further includes payoff and take-up reels for the elongated strip, such as disclosed in the previously mentioned US. Pat. No. 3,735,728, the disclosure of which is hereby incorporated by reference. As the masking wheel 1 1 rotates, the substrate strip is unwound from the payoff reel and carried by the masking wheel to the take-up reel. ln actual practice, it is the take-up reel which is driven to move the strip, and the strip frictionally drives the masking wheel which is otherwise freely rotatable.

It is while the strip 17 is positioned on the masking wheel 11 bridging the gap 19 between the

rims

14 and 16 that material is deposited through the gap onto a stripe on the strip delimited thereby. To this end, a source of the material to be deposited is positioned inwardly of the rims. That is, as is illustrated in FIG. 1, a crucible 21 for holding the material to be deposited is positioned within the interior of the masking wheel. An electron gun schematically illustrated at 22 is provided for bombarding the material within the crucible with electrons to thereby evaporate such material and form a vapor of the same. Such vapor will condense on surfaces within the line of sight of the source material and thereby coat such surfaces. The masking wheel 11 will shield all of the substrate strip from the coating material vapor except for that stripe area of the same bridging the gap 19 between the

rims

14 and 16. Thus, such area of the strip will be coated as desired upon passage of such strip through the deposition area, i.e., that area along its path of travel within which vapor from the source is able to deposit thereon.

As mentioned previously, one problem with prior apparatus of this nature is that either the masking rims 14 and 16 are secured together in a manner which prevents continuous deposition on the stripe for the full length of the gap 19, or else such rims are independently mounted with the result that they do not maintain an exact parallel relationship while rotating. As a particularly salient feature of the instant invention, it is constructed to avoid these problems. In this connection, the rims l4 and 16 are rigidly secured together by connectors 23 which extend therebetween at locations which are spaced circumferentially of the rims. Such connectors thus normally maintain the rims at a predetermined spacing apart for their full circumferences, thereby assuring that they maintain their spatial relationship so that the width of the gap 19 does not vary. As mentioned previously, however, whenever connectors of one sort or another have been used to secure masking rims together, it resulted in certain locations of the substrate strip bridging the gap between the rims not receiving coating material. As a particularly salient feature of the instant invention, it is so constructed that such problem is minimized. More particularly, as best seen from both FIGS. 2 and 3, the connectors 23 are spaced radially inwardly of the locations of the recesses 18 and, hence, the substrate strip to be coated. Moreover, the source of the coating material is positioned substantially above the axis of rotation of the masking wheel, indicated at 24. Most-desirably, the source 21 is so positioned relative to the location of the connectors and the curvature of the rims that any portion of the strip area bridging the gap 19 shielded by a connector from the source at any position of such portion within the deposition area will be exposed to material from the source at some other position of such portion within the deposition area.

The combination of the above connector and source locations with respect to the rims and the axis of rotation of the masking wheel can result in all areas of the substrate strip bridging the gap 19 being exposed to material emanating from the source during passage of such strip through the deposition area. For a clearer understanding of this, reference is made to FIG. 2, which schematically illustrates the areas of the substrate strip which are shielded from the source 21 at any given time by the connectors 23. That is, at any given time the connectors 23 will shield from the source 21 those areas on the strip indicated by the brackets 26. It will be noted that as the masking wheel rotates in the direction indicated by the lines 27, each of the connectors will move through the deposition area on an arcuate path having the axis of rotation 24 as its center. However, because the connectors are spaced inwardly of the substrate strip and the source is positioned off the axis of rotation, the shadow or area shielded from the source by any particular connector will shift along the gap as the rims i'otate."l"o illustrate this, dotted lines are used in lFlG. 2 to show a radial projection of the connectors onto the substrate strip. it will be recognized that because such projections are radial, i.e., represent projections talten from the axis of rotation of the wheel, they will not shift as the wheel rotates. Thus the changing relationship of the shielded areas 2b to the dotted line projections 28 shows the shift of the shielded areas. if one considers a point 29 on the substrate strip, for example, which is generally in the middle of the shielded area upon the substrate strip entering the left-hand side of the deposition area, it will be seen that by the time the mashing wheel has rotated the portion of the substrate having the point 29 generally half-way through the deposition area, it will be outside of the area shielded by the connector. That is, it will be at the location of the point 29' near the top of the path where it will clearly be within the line-of-site of the source. By the time the point 2% on the substrate strip reaches the right-hand edge of the deposition area, it will be in the relationship to the shadow area 26 of the point 29".

The specific geometrical relationships of the parts necessary to achieve any desired ratio of shielded to unshielded path lengths is easily determined by line-ofsite ray projection analysis. it should be noted, though, that the deposited material will actually curve around the connectors so that the area shielded by each will have a width slightly less than that of a light shadow. From the practical standpoint, it is preferred that the ratio of the width of each connector to the distance between the connector and the substrate surface to be coated be less than one. Moreover, the ratio of the width of each connector to the distance between adjacent connectors is preferably less than 1 .5, and the distance between each connector and the surface to be coated should be no greater than one-fourth the minimum distance between the source and the connector. in one embodiment of the invention, the radius of curvature of the wheel at the location at which the sub strate strip rides thereon was chosen to be 15 inches, the width of each connector one-quarter inch, the distance between each connector and the surface to be coated was selected to be 1 inch, and the minimum distance between the source and a connector was 4.5 inches. The distance between adjacent connectors was approximately 2 inches.

Most desirably, each of the connectors 23 is ofa heat conductive material and is in good thermal contact with each of the rims. Each connector will then act as a thermal, bridge between the rims which will tend to maintain the same at the same temperature. This will minimize the possibility of differential thermal expansion of the rims and, hence, the substrate riding on only one of such rims rather than both. in the embodiment being described the connectors are integrally secured to both of the rims and tie the same together into a rigid structure. That is, the two rims M and iii in the con nections 23 are of a one'piece construction. this construction assures both the desired good thermal contact and the rigidity preferred to prevent variations in the width of the coated substrate area.

The substrate strips from which lead frames are made sometimes have imperfections at their edges which prevent a proper fitting of the strip within the track de lined in the outer periphery of the: masking wheel by the recesses ill. Flt ll illustrates an embodiment of the invention which assures that such imperfections will not'result in the substrate strip running out of such track. More particularly, rather than each of the connectors being integrally secured to both of the rims to tie the same together into a rigid structure, the connectors are adapted to allow the rims to separate somewhat in order to accommodate such imperfections. More particularly, each of the connectors is in the form of a bolt extending from a first one ill of the rims slideably into a bore in the other of such rims, rim 32. As shown, the bolt 36] has an inwardly tapered portion defining a shoulder 33 which mates with a corresponding shoulderdd in the rim 32. it will be recognized that because of such confronting shoulder relationship, sliding of the rim inwardly on the bolt 3ft beyond a predetermined extend is prevented.

it coil spring 36 is maintained in compression between the rim T52 and the bolt Fill to resiliently urge the

shoulders

33 and 34 into engagement. That is, the spring 36 is received within an enlarged part of the bore through rim 32 opening onto its exterior side surface and abuts against a washer 37 held on pin 30 by a nut 38 threadably received on the latters free end.

While not shown, it will be recognized that a plurality of the bolt connectors are spaced circumferentially about the masking wheel in the same manner as are the connectors in the previously described embodiment. With this construction, it will be recognized that the connectors will prevent contraction of the predetermined spacing between the rims because of the engagement of the cooperating shoulders. However, because of the spring arrangement, each connector will be responsive to any force tending to separate the rims by allowing such separation. Thus, any imperfection on the edge of a substrate strip which otherwise might prevent the strip from entering the track will tend to force the rims apart so that it can be accommodated. The bolt and spring-nut connector arrangement has the added advantgage of enabling the rims to be disassembled from one another to facilitate cleaning. However, when such rims are again assembled, the cooperating shoulders assure that the proper spacing is obtained without the necessity of a complex aligning procedure.

While as mentioned previously, there will be some variation in the thickness of the coating applied to the substrate in view of portions thereof being shielded at least some of the time by the connectors from the material source, the degree of such variation can generally be minimized to an acceptable amount by an appropriate choice of the geometrical relationships. There are some coating applications, however, in which appreciable variations cannot be tolerated. F 16. d illustrates another embodiment of the invention which results in a further reduction in coating thickness variation. This embodiment is basically the same as the previously de scribed embodiments, except that rather than only one source of coating material being provided, two of such sources it and 42 are shown off the axis of rotation of the masking wheel. Such sources are so positioned inwardly of the rim relative to the connectors and the curvature of the rim that when any portion of the strip is shielded from one of the source by a connector it will be exposed to material emanating from the other of such sources. This is illustrated for the area 4 3 which is shielded by the connector 44 from the source 41. As shown, at the same time the area 43 is so shielded it is exposed to material emanating from the source 42. Thus, there is no time during the passage of the substrate strip through the deposition area that all portions of the same do not receive material. The combination of multiple sources with otherwise carefully chosen geometrical relationship will reduce thickness variations in the coating to within acceptable tolerances for most all applications.

While the invention has been described in connection with apreferred embodiment thereof, it will be appreciated by those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. For example, the novel features of the second and third embodiments can be incorporated into the same apparatus, if desired. It is therefore intended that the coverage afforded applicant be limited only by the claims and their equivalent language.

I claim:

1. In a vacuum deposition apparatus for depositing material in a stripe on an elongated substrate strip comprising:

l. a masking wheel for delimiting an area of said substrate strip upon which said material is deposited during passage of said strip through a deposition area, said wheel including:

a. a pair of axially aligned and spaced apart masking rims having generally the same outer peripheral circumferences and upon which said strip rides bridging the gap therebetween during said passage through said deposition area, and

b. a plurality of connectors extending between said rims and securing the same together at locations spaced circumferentially of said rims to normally maintain the same a predetermined spacing apart defining said stripe;

2. a source of said material to be deposited positioned inwardly of said rims whereby upon rotation of said wheel to carry said strip on said rims through said deposition area, material from said source will be deposited on the area of said strip exposed between said rims;

3. each of said connectors extending between said rims at a location between said strip and said source which is spaced inwardly of the location at which said strip bridges the gap between said rims, and said source being positioned inwardly of said rims at a location which is off the axis of rotation thereof, whereby the portions of said strip area between said rims which are shielded by said connectors from. the deposition of said materials shifts along said area as said rims rotate so that all portions of said area of said strip exposed between said rims are exposed to deposited material during passage through said deposition area.

2. The vacuum deposition apparatus of claim 1 wherein each of said connectors is of a heat conductive material and is in good thermal contact with each of said rims whereby each connector acts as a thermal bridge tending to maintain said rims at the same temperature.

3. The vacuum deposition apparatus of claim 1 wherein said source is positioned relative to the connectors and said rims have a curvature such that any portion of said strip area shielded from said source by a connector at any selected position of said portion within said deposition area will be exposed to material from said source at some other position of said portion within said deposition area upon rotation of said masking wheel to carry said strip through said area.

4. The vacuum deposition apparatus of claim 1 wherein each of said connectors is integrally secured to both of said rims to tie the same together into a rigid structure.

5. The vacuum deposition apparatus of claim 1 wherein each of said connectors is adapted to prevent contraction of said predetermined spacing of said rims while being responsive to forces tending to separate said rims by allowing such separation.

6. The vacuum deposition apparatus of claim 5 wherein each of said connectors is a bolt extending from a first one of said rims slideably into a bore in the other of such rims, said bolt and said bore having cooperating shoulders mating to prevent movement of said rim with said bore toward said first rim beyond a predetermined location, and spring means associated with said bolt for resiliently urging said shoulders into engagement.

7. The vacuum deposition apparatus of claim 1 wherein at least two sources of said material to be deposited are positioned inwardly of said rim at locations relative to the connectors and the curvature of said rims at which when any portion of said strip area is shielded by a connector from one of said sources, it will be exposed to material emanating from the other of said sources.

Claims

1. In a vacuum deposition apparatus for depositing material in a stripe on an elongated substrate strip comprising: 1. a masking wheel for delimiting an area of said substrate strip upon which said material is deposited during passage of said strip through a deposition area, said wheel including: a. a pair of axially aligned and spaced apart masking rims having generally the same outer peripheral circumferences and upon which said strip rides bridging the gap therebetween during said passage through said deposition area, and b. a plurality of connectors extending between said rims and securing the same together at locations spaced circumferentially of said rims to normally maintain the same a predetermined spacing apart defining said stripe; 2. a source of said material to be deposited positioned inwardly of said rims whereby upon rotation of said wheel to carry said strip on said rims through said deposition area, material from said source will be deposited on the area of said strip exposed between said rims; 3. each of said connectors extending between said rims at a location between said strip and said source which is spaced inwardly of the location at which said strip bridges the gap between said rims, and said source being positioned inwardly of said rims at a location which is off the axis of rotation thereof, whereby the portions of said strip area between said rims which are shielded by said connectors from the deposition of said materials shifts along said area as said rims rotate so that all portions of said area of said strip exposed between said rims are exposed to deposited material during passage through said deposition area.

3. each of said connectors extending between said rims at a location between said strip and said source which is spaced inwardly of the location at which said strip bridges the gap between said rims, and said source being positioned inwardly of said rims at a location which is off the axis of rotation thereof, whereby the portions of said strip area between said rims which are shielded by said connectors from the deposition of said materials shifts along said area as said rims rotate so that all portions of said area of said strip exposed between said rims are exposed to deposited material during passage through said deposition area.