Apparatus for electroplating an article

Abstract

An apparatus for electroplating an article, such as a printed circuit board, includes a tank filled with electrolytic solution, a clamp for retaining the article fixed in place within the solution and a movable roller assembly disposed within the solution. The roller assembly includes a pair of vertically disposed, parallel rollers that are rotatably coupled to a rigid frame, with one roller preferably being spring biased towards the other roller. In use, the application of electrical current causes metal ions present in the solution to plate out on the article. To promote greater plating within through-holes or other similar surface depressions in the article, the roller assembly is linearly displaced by a motor-driven linkage so that the pair of rollers squeegee opposing surfaces of the article.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patent application Ser. No. 11/606,629, filed Nov. 30, 2006 which, in turn, is a continuation of U.S. patent application Ser. No. 10/856,505, filed Jun. 1, 2004, both of said applications being incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to electroplating equipment and more particularly to equipment used to electroplate articles which include holes and/or surface depressions.

Electroplating is a well-known and widely used process which uses electrical current to deposit a thin layer of metal with some particular property (e.g., conductivity, abrasion and wear resistance, corrosion protection, lubricity, improvement of aesthetic qualities, etc.) onto an article that lacks said property.

Specifically, in one well-known form of electroplating, electrodes are immersed in a tank filled with an electrolytic solution that serves to create a closed electrical circuit therebetween. One or more of the electrodes (i.e., the electrodes that are to be plated) serve as the cathode of the circuit and, as such, are connected to the negative terminal of an external direct current (DC) power supply, such as a battery or rectifier with variable voltage and amperage control. The remaining electrodes (i.e., the electrodes constructed of the particular metal to be plated onto the cathode) serve as the anode of the circuit and, as such, are connected to the positive terminal of the DC power supply. The supply of voltage to the closed circuit causes metal ions present in the electrolytic solution to lose their charge and plate out (i.e., accumulate, deposit) on the cathode. The anode serves to replenish the supply of metal ions in the electrolytic solution during the plating process.

Electroplating is commonly utilized during the manufacture of printed circuit boards to deposit a conductive material, such as nickel or copper, onto a non-conductive substrate. Upon completion of the electroplating process, the conductive material deposited on the substrate is etched in a particular pattern to create a number of conductive pathways, or traces. In this manner, the conductive pathways can be used to electrically connect components mounted on the circuit board.

Circuit board electroplating is commonly performed in the following manner. Each circuit board to be plated is attached to a corresponding conductive frame which is, in turn, connected to the negative terminal of the power supply. Each frame is then mounted onto an enlarged tank filled with an electrolytic solution so that the circuit board is completely immersed within the solution. It should be noted that each frame is traditionally mounted onto the tank so that the circuit board extends in a substantially vertical position, thereby enabling for (1) a greater quantity circuit boards to be disposed in tank at the same time and (2) easier access to each circuit board within the tank. With the circuit board immersed within the solution, one or more pairs of metallic members (e.g., rods or blocks constructed of copper) are connected to the positive terminal of the power supply and are similarly immersed within the electrolytic solution on opposite sides of the circuit board. Accordingly, with voltage being supplied from the power source, each circuit board (and its corresponding frame) serves as the cathode of the closed circuit and each metallic member serves as the anode of the closed circuit. In this manner, it is to be understood that the surfaces of the circuit board that are exposed to metal ions in the electrolytic solution become plated with conductive material. It should be noted that metal ions accumulate on the exposed portions of the circuit board until either (1) the supply of voltage to the circuit is withdrawn or (2) metal ions no longer remain available in the electrolytic solution.

As can be appreciated, printed circuit boards are commonly provided with a number of holes and/or surface depressions. For example, many printed circuit boards are provided with a large quantity of through-holes that extend transversely through the circuit board substrate, with the barrel of each through-hole being plated with a conductive material. In this manner, components can be electrically connected to the printed circuit board by (1) positioning each lead for the component within a corresponding through-hole in the circuit board and (2) filling each through-hole with a conductive material, such as solder.

The above-described circuit board electroplating process is commonly used to conductively plate the barrel of through-holes that extend transversely through the circuit board substrate. However, it has been found that the effectiveness of electroplating the barrel of through-holes is compromised due to (1) the relatively small cross-sectional diameter of each hole and (2) the limited flow of metal ions in the electrolytic solution through each through-hole since the longitudinal axis of each hole is horizontally disposed.

Various techniques have been incorporated into the traditional electroplating process to stimulate the flow of electrolytic solution and thereby increase the amount of metal plating on an article.

As an example, it is well-known in the art to periodically agitate the electrolytic solution to promote greater amounts metal ion deposition onto an article. Agitation of the electrolytic solution is often accomplished by displacing one or more air sparger units within the solution. Each air sparger unit is commonly constructed using a 0.25-0.50 inch PVC pipe that includes a plurality of spaced apart holes. In use, clean air (e.g., nitrogen) is pumped through the pipe at high pressure and, in turn, exits through the spaced apart holes in the pipe as bubbles. The creation of these bubbles serves to help agitate the solution and break hydrogen gas bubbles that may collect around the board.

As another example, it is well-known to move and/or vibrate the article to be plated in order to promote greater amounts of metal ion deposition. In U.S. Pat. No. 5,167,779 to H. J. Henig, there is disclosed a process and apparatus for obtaining an intensive and continuous exchange of electrolyte on the surfaces of workpieces subjected to chemical or electrolytical treatments wherein the exchange is achieved by subjecting the workpieces to strong pulsating oscillations of frequency of at least 1 Hz and of an amplitude of less than 10 mm, when immersed in the electrolyte. The vibrations are transmitted from an oscillation generator mounted on a workpiece carrier, such as a rack or a rotating dipping drum. These high frequency low amplitude oscillations may be combined with low frequency, relatively long oscillations occurring simultaneously. The oscillation generator is arranged on the individual transportable workpiece carriers. The workpieces may be boards for printed circuits having through holes or a pourable mass of parts.

Although well-known in the art, the techniques described above for improving metal ion deposition have been found to introduce a number of notable drawbacks.

As a first drawback, the above-described techniques have been found to be inadequate when used to plate the barrel of circuit board through-holes which extend axially in a horizontal manner. Specifically, the above-described electroplating techniques produce a deposition layer on the barrel of each through-hole that is of limited thickness which, in turn, can jeopardize the quality of the electrical connection established between electrical components and the printed circuit board on which the components are mounted, which is highly undesirable. Consequently, these types of electroplating processes are often significantly extended until the deposition layer in each though-holes is adequate. However, this results in (1) a substantial increase in the deposition layer on the top and bottom surfaces of the circuit board, (2) an increase in manufacturing costs, and (3) a greater time requirement, all of which are highly undesirable.

As a second drawback, it has been found that the use of certain agitation units to improve the flow of electrolytic solution are potentially harmful to the environment, which is highly undesirable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new and improved apparatus for electroplating an article, such as a printed circuit board, the article including enlarged, flattened top and bottom surfaces and one or more through-holes extending transversely therethrough.

It another object of the present invention to provide an apparatus as described above which adequately plates the barrel of each through-hole in the article without significantly increasing the amount of deposition on each of the top and bottom surfaces.

It is yet another object of the present invention to provide an apparatus as described above which limits the risk of potentially harmful environmental conditions.

It is still another object of the present invention to provide an apparatus as described above which has a limited number of parts, which is quick and easy to use and which is inexpensive to manufacture.

Accordingly, there is provided an apparatus for electroplating an article, the article including substantially flat front and rear surfaces, the apparatus comprising (a) a tank shaped to define an interior cavity; (b) a clamp adapted to fixedly support the article within the interior cavity of the tank; (c) a roller assembly adapted to squeegee the front and rear surfaces of the article; and (d) a linkage for linearly displacing the roller assembly within the interior cavity of the tank.

Various other features and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration, a specific embodiment for practicing the invention. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings wherein like reference numerals represent like parts:

FIG. 1 is a fragmentary, front perspective view of an apparatus for electroplating an article which has been constructed according to the teachings of the present invention, the apparatus being shown with an article attached thereto;

FIG. 2 is an enlarged, fragmentary, top perspective view of the roller assembly, support rail and tank shown in FIG. 1; and

FIG. 3 is an enlarged, front plan view of one of the clamps shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown an apparatus for electroplating an article 10, the apparatus being constructed according to the teachings of the present invention and identified generally by reference numeral 11. As will be described in greater detail below, apparatus 11 is specifically designed to ensure adequate electroplating within any holes, recesses or other similar types of surface depressions provided in article 10.

For purposes of simplicity only, article 10 is represented herein as being in the form of a conventional printed circuit board that includes enlarged, flattened front and rear surfaces 13-1 and 13-2 as well as a plurality of transversely extending through-holes 15. Furthermore, the inherent benefits associated with apparatus 11 will be described in connection with the plating of the barrel of each through-hole 15 (i.e., the hole wall) in an efficient manner.

However, it is to be understood that apparatus 11 is not limited to the plating of printed circuit boards. Rather, it is to be understood that apparatus 11 is designed for use in connection with any flattened article 10 that commonly electroplated in the art.

In addition, it is to be understood that the advantages inherent in apparatus 11 are not limited to the plating of transverse through-holes 15 in article 10. Rather, it is to be understood that apparatus 11 is useful in electroplating other forms of surface depressions (e.g., grooves, partial holes, etc.) without departing from the spirit of the present invention.

Electroplating apparatus 11 comprises a rectangular tank 21, a pair of clamps 23-1 and 23-2 for supporting the article 10 to be electroplated, a roller assembly 25 for squeegeeing conductive material that accumulates on front surface 13-1 and/or rear surface 13-2 of article 10 during the electroplating process, and a motor-driven linkage 27 for linearly driving roller assembly 25 within tank 21.

Tank 21 is constructed out of a rigid, durable and non-conductive material, such as plastic, and includes a flat bottom panel 29 and four side panels 31-1 through 31-4 that together define an interior cavity 33. A flat rectangular flange, or frame, 35 is formed on the free ends of side panels 31 and defines an open top through which interior cavity 33 can be accessed. A continuous, horizontal strengthening rib 36 is additionally formed onto side panels 31 to improve the structural integrity of tank 21.

A pair of support blocks 37-1 and 37-2 are fixedly mounted on opposite ends of flange 35. As seen most clearly in FIG. 2, each support block 37 is shaped to define a channel 39 which is generally square-shaped in lateral cross-section. As will be described further below, blocks 37 serve to both support and guide a component of linkage 27 during the linear displacement of roller assembly 25.

Tank 13 is at least partially filled with an electrolytic solution (not shown). The electrolytic solution represents any solution that includes metal (e.g., copper, nickel) dissolved and suspended in a liquid as a metal ion. As will be described further below, electrolytic solution creates a closed electric circuit between the one or more anodes and cathodes of the electroplating system.

A pair of cathode bars 43-1 and 43-2 are fixedly mounted onto opposite ends of flange 35. Each cathode bar 43 is constructed out of a conductive material, such as copper, and is electrically connected to the negative terminal of an external DC power supply, as will be described further in detail below.

Referring now to FIG. 3, each clamp 23 comprises an elongated cathode rod 45 that is constructed out of a conductive material, such as copper. An elongated sleeve 47 is shown mounted over cathode rod 45 and extends the majority of its length. Sleeve 47 is preferably constructed out of material that serves to preserve cathode rod 45.

An L-shaped metal clip 49 and a U-shaped metal hook 50 are fixedly mounted onto one end of cathode rod 45. Clip 49 is designed to receive a portion of a cathode bar 43. Clip 49 is additionally shaped to receive a threaded screw 51. In this manner, with cathode bar 43 positioned within clip 49, screw 51 can be driven into frictional engagement with cathode bar 43 to fixedly couple clamp 23 thereto. In this manner, clamp 23 is electrically connected to cathode bar 43 and, as such, acts as part of the cathode in the closed circuit. Although not shown herein, it is to be understood that clamp 23 may be electrically connected to cathode bar 43 by hanging metal hook 50 directly thereon (rather than using clip 49).

A plurality of generally C-shaped clips 53 are fixedly mounted onto sleeve 47 in a spaced apart relationship along its length. Each clip 53 is sized and shaped to receive an edge of article 10. Each clip 53 is additionally shaped to receive a corresponding threaded screw 55. In this manner, with an edge of article 10 aligned within clips 53, screws 55 can be driven into frictional engagement with a surface 13 of article 10 to fixedly couple article 10 thereto. By connecting article 10 to clamp 23 in this manner, it is to be understood that article 10 acts as part of the cathode of the closed circuit, as will be described further below.

As seen most clearly in FIG. 2, roller assembly 25 comprises a pair of parallel rollers 57-1 and 57-2 that are connected to a rigid, stainless steel frame, or collar, 59.

Preferably, each roller 57 is connected to frame 59 using one or more fasteners 61 (e.g., an allen screw), fasteners 61 preferably enabling each roller 57 to spin freely relative to frame 59. It is to be understood that, in place of the aforementioned arrangement, a more complex mechanical device (e.g., a rotatable bushing or bearing assembly) may be used to enable each roller 57 to spin freely relative to collar 59. At the free end of each roller 57, a lock bolt 63 is mounted which can be tightened against frame 59 to prevent each roller 57 from free spinning, which may be desirable in certain applications.

Rollers 57 are vertically disposed in a parallel manner and are spaced apart a fixed distance D (as represented in FIG. 2). Preferably, at least one roller 57 is spring biased towards the other. Accordingly, upon the application of a suitable outward force thereon, the spring biased roller 57 would displace away from the opposite roller 57, the spring biased roller 57 traveling within a narrow slot (not shown) provided in collar 59. In this manner, roller assembly 25 can be used to accommodate articles 10 of varying thicknesses (e.g., in the range of approximately 0.25-0.62 inches), which is highly desirable.

It should be noted that in place of the spring biased configuration noted above, roller assembly 25 may be designed such that each roller 57 can be re-positioned into one of a plurality of fixed settings to adjust the relative spacing therebetween. Once disposed in its desired position, each roller 57 can be locked in place with a fastening element (e.g., a bolt) to maintain constant spacing therebetween.

As can be appreciated, the spacing set between the pair of rollers 57 is dependent upon the particular application and user preferences. For example, in some applications, it may be desirable for rollers 57 to barely touch the top and bottom surfaces 13-1 and 13-2 of article 10. In other applications, it may be desirable for rollers 57 to apply a greater degree of pressure on article 10 so as to burnish surfaces 13. In this manner, rollers 57 serve to limit the degree of plating on top and bottom surfaces 13-1 and 13-2 without compromising the efficiency of plating within through-holes 15, which is highly desirable.

Each roller 57 comprises a roller core 65 and a sleeve 67 slidably disposed over core 65.

Core 65 is preferably constructed out of a titanium-sleeved copper (i.e., a copper core with a titanium outer sleeve). As can be appreciated, the titanium serves to protect to protect the copper core from depletion during the plating operation.

Sleeve 67 is slidably mounted over core 65 in a fitted relationship relative thereto, with a fastening element (e.g., a washer and screw) provided at the free end of each roller 57 to prevent sleeve 67 from sliding off of core 65. Preferably, sleeve 67 is constructed out of polyvinyl alcohol (PVA) which, due to its sponge-like qualities, would not damage surfaces 13 of article 10. However, it should be noted that sleeve 67 could be constructed using other similar materials, such as polypropylene, without departing from the spirit of the present invention.

Frame 59 additionally includes a pair of spaced apart, upwardly extending support rods 69-1 and 69-2 which extend transversely through a pair of spaced apart support plates 71-1 and 71-2. A fastening device 73 (namely, a collar and threaded screw) is mounted on the end of each rod 69 to retain plates 71 on rods 69. As will be described further below, support plates 71 are used to couple roller assembly 25 to linkage 27.

Referring back to FIG. 1, linkage 27 comprises a motor 74, an enlarged rotatable disk 75 mounted on motor 74, a travel board 77 coupled to disk 75, and a linearly displaceable rail 79 affixed to travel board 77. As will be described further in detail below, linkage 27 serves to linearly displace roller assembly within tank 21 in such a manner so as to squeegee surfaces 13 of article 10.

Motor 74 is connected to side panel 31-4 of tank 21 by a support member 81 which serves to space motor 74 adequately away from side panel 31-4. Motor 74 represents any conventional rotary motor which is well-known in the art.

Disk 75 is fixedly mounted onto the output shaft for motor 74. Accordingly, it is to be understood that activation of motor 74 serves to rotate disk 75 (as represented by arrow A in FIG. 1). Disk 75 is preferably constructed out of rigid and durable material and includes a pin 83 that extends orthogonally upward from the top surface of disk 75 at a location other than at its center.

Travel board 77 is represented herein as being in the form of a rectangular block that is provided with an elongated, longitudinal slot 85. As can be seen in FIG. 1, travel board 77 is mounted on disk 75 such that pin 83 protrudes through slot 85. As a result, as disk 75 rotates, pin 83 travels back and forth within slot 85 and, in turn, linearly displaces travel board 77 back and forth.

Rail 79 is represented herein as being in the form of an elongated rod which is generally rectangular in lateral cross-section. One end of rail 79 is affixed to travel board 77 (e.g., using screws), with the remainder of rail 79 extending longitudinally above tank 21. As can be seen, rail 79 slidably protrudes through channel 39 in each support block 37. Accordingly, it is to be understood that support blocks 37 serve to limit rail 79 to linear displacement above tank 21 (in the direction represented by arrow B in FIG. 1).

As seen most clearly in FIG. 2, rail 79 is sandwiched between plates 71-1 and 71-2 of roller assembly 25 and is held fixed in place using fastening devices 73. In this manner, it is to be understood that roller assembly 25 is fixedly mounted onto rail 79.

As seen most clearly in FIG. 1, electroplating apparatus 11 additionally comprises six copper rods 87 that are fully immersed within the electrolytic solution, with three rods 87 disposed vertically against the inner surface of side panel 31-1 and the other three rods 87 disposed vertically against the inner surface of opposing side panel 31-3. In this manner, each rod 87 is disposed roughly the same distance (approximately 10-12 inches) away from a corresponding surface 13 on article 10.

Electroplating apparatus 11 further comprises a direct current (DC) power supply 89, such as battery or rectifier with variable voltage and amperage control, which is located outside tank 21. Each copper rod 87 is electrically connected to the positive terminal 91 for DC power supply 89. In addition, each bar 43 is electrically connected to the negative terminal 93 for DC power supply 89. For purposes of simplicity only, the above-described connections are not shown in FIG. 1.

Although not shown herein, electroplating apparatus 11 also preferably includes an air sparger unit that is located within tank 13 against the inner surface of bottom panel 29. The air sparger unit is designed to expel clean air bubbles into electrolytic solution in order to stimulate electroplating on the intended article 10.

Apparatus 11 can be used to electroplate an article 10 in the following manner. Specifically, with apparatus 11 configured in the manner described above, the supply of voltage from DC power supply 89 causes metal ions present in the electrolytic solution to lose their charge and plate out (i.e., accumulate, deposit) on article 10, with rods 87 serving to replenish the supply of metal ions in the solution over time.

It should be noted that the portions of article 10 that are directly exposed to the metal ions in solution 41 experience the greatest degree of plating. Specifically, metal ions present in the electrolytic solution tend to plate out on front and rear surfaces 13-1 and 13-2 of article 10. In addition, metal ions present in the electrolytic solution tend to plate out on the barrel of each through-hole 15.

During the above-described electroplating process, roller assembly 25 is driven against front and rear surfaces 13-1 and 13-2 of article 10 to promote greater plating within through-holes 15. Specifically, activation of motor 74 causes enlarged disk 75 to rotate about its center which, in turn, serves to linearly displace travel board 77 back and forth. The linear displacement of travel board 77 serves to similarly displace rail 79, with support blocks 37 ensuring that the displacement is linear in nature (as represented by arrow B in FIG. 1). The linear displacement of rail 79 in turn serves to displace roller assembly 25 within tank 21.

As roller assembly 25 is linearly displaced, sleeve 67 of each roller 57 is disposed in contact against a corresponding surface 13 of article 10, the degree of pressure exerted by each roller 57 against article 10 being largely dependent on the spacing between rollers 57 (or, if included, the force of any spring used to bias one roller 57 inward). As the roller assembly 25 advances linearly, each roller 57 preferably rolls along a corresponding surface 13 of article. In this manner, it is to be understood that each roller 57 effectively acts as a squeegee which results in (1) a reduction in the amount of metal deposition on front and rear surfaces 13-1 and 13-2 and (2) an increase in the amount of metal deposition within through-holes 15, which is a principal object of the present invention.

The embodiment shown in the present invention is intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. For example, it is to be understood that additional roller assemblies 25 could be implemented into apparatus 11 to allow for simultaneous, efficient electroplating of multiple articles 10 disposed within the same tank 21. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims.

Claims

1. An apparatus for electroplating an article, the article including substantially flat front and rear surfaces, the apparatus comprising:

(a) a tank shaped to define an interior cavity;

(b) a clamp adapted to fixedly support the article within the interior cavity of the tank;

(c) a roller assembly adapted to squeegee the front and rear surfaces of the article; and

(d) a linkage for linearly displacing the roller assembly within the interior cavity of the tank.

2. The apparatus as claimed in claim 1 wherein the roller assembly comprises,

(a) a rigid frame, and

(b) a pair of parallel rollers coupled to the rigid frame.

3. The apparatus as claimed in claim 2 wherein each of the pair of parallel rollers is vertically disposed and is adapted to contact a corresponding surface on the article in order to squeegee material that has accumulated on the surface during the electroplating process.

4. The apparatus as claimed in claim 3 wherein each of the pair of parallel rollers can spin freely relative to the rigid frame.

5. The apparatus as claimed in claim 3 wherein the pair of parallel rollers is spaced apart a fixed distance.

6. The apparatus as claimed in claim 3 wherein the spacing between the pair of parallel rollers can be adjusted.

7. The apparatus as claimed in claim 6 wherein at least one of the pair of parallel rollers is spring biased towards the other of the pair of parallel rollers.

8. The apparatus as claimed in claim 3 wherein each roller comprises,

(a) a core, and

(b) a sleeve disposed over the core.

9. The apparatus as claimed in claim 8 wherein the core is constructed out of a titanium-sleeved copper.

10. The apparatus as claimed in claim 9 wherein the sleeve is constructed out of polyvinyl alcohol (PVA).

11. The apparatus as claimed in claim 1 wherein the apparatus additionally comprises,

(a) a direct current (DC) power supply which comprises a positive terminal and a negative terminal,

(b) a cathode bar, the clamp being conductively coupled to the negative terminal of the DC power supply through the cathode bar, and

(c) one or more metal rods disposed within the interior cavity of the tank, each of the one or more metal rods being electrically connected to the positive terminal of the DC power supply.

12. The apparatus as claimed in claim 1 wherein the linkage comprises,

(a) a motor,

(b) a rotatable disk fixedly mounted on the motor,

(c) a travel board slidably mounted on the rotatable disk, and

(d) a rail fixedly connected to the travel board, the rail being fixedly

connected to the roller assembly.

13. The apparatus as claimed in claim 12 wherein the tank comprises a flat bottom panel and four side panels that together define the interior cavity.

14. The apparatus as claimed in claim 13 wherein the tank additionally comprises a pair of fixedly mounted support blocks.

15. The apparatus as claimed in claim 14 wherein the pair of support blocks limit the rail to displacement along a linear path.

16. The apparatus as claimed in claim 15 wherein the rotatable disk includes a fixed pin which is sized and shaped to protrude through a longitudinal slot formed in the travel board.

17. A method of manufacturing an article, the article including substantially flat front and rear surfaces; said method comprising the steps of:

(a) electroplating the article, the electroplating step resulting in a layer of metal being deposited on the front and rear surfaces of the article, and

(b) squeegeeing at least a portion of the layer of metal deposited on the front and rear surfaces of the article using a roller assembly.

18. The method as claimed in claim 17 wherein the roller assembly is linearly movable.

19. The method as claimed in claim 18 wherein the roller assembly comprises,

(a) a rigid frame, and

(b) a pair of parallel rollers coupled to the rigid frame.

20. The method as claimed in claim 19 wherein, as part of the squeegeeing step, each of the pair of parallel rollers contacts a corresponding surface on the article.