Abstract:
A method for applying a strike voltage to one or more substrates during plating. During this method, the substrates are moved in a planetary manner while being held at their exterior edges by a set of parallel mandrels. (The substrates are held in a mutually parallel orientation, typically vertically, during plating.) A voltage is applied to the substrates via a contact pin, a contact plate, a set of ball bearings, a rack end-plate, and the mandrels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/853,953, which was filed on May 26, 2004. 

   BACKGROUND OF THE INVENTION 
   This invention pertains to methods for applying a voltage to a substrate during plating. This invention also pertains to apparatus for applying a voltage to a substrate during plating. 
   During various industrial processes one plates a material onto a substrate. For example, U.S. Provisional Patent Application No. 60/535,380 filed by Bajorek et al. discusses a process whereby one plates NiP onto a disk-shaped metallic substrate during the course of making a master or a stamper used during CD and DVD manufacturing. (The &#39;380 provisional application is incorporated herein by reference.) Plating is performed during numerous other industrial processes, e.g. magnetic disk manufacturing. 
   During some plating processes, plating is “electroless”, i.e. a voltage is not applied to the substrate being plated. We have found that initiation of electroless plating can be enhanced by applying a “strike voltage” to the substrates. It would be desirable to provide plating apparatus that facilitates application of such a voltage. 
   SUMMARY OF THE INVENTION 
   Apparatus for plating material onto one or more substrates comprises a set of elongated arms (e.g. mandrels) for holding the outer edge of the substrates. In one embodiment, the substrates are electrically conductive, and can be disk-shaped. The arms are connected to a connecting member, which in turn is coupled to a source of electrical power. (Typically, the connecting member is provided on one end of the arms, and a second connecting member is connected to the other end of the arms.) The structure comprising the arms, connecting member and substrates are placed into a plating bath. Rotational motion and electrical power are imparted to the connecting member during at least a portion of the plating process. (The substrates are typically rotated during the entire plating process, but electrical power is typically only imparted to the substrates during a portion of the process.) 
   In one embodiment, the substrates are moved in a planetary manner, e.g. using a gear system that imparts planetary motion. At least one of the gears comprises an electrically conductive region that is electrically coupled to the connecting member. The electrically conductive region can be a plate affixed to a surface of the gear. An electrical path (e.g. comprising a wire) extends from a power source outside the plating bath (e.g. a voltage source) into the bath to a contact member that is in sliding contact with the conductive region to thereby apply electrical power to the substrates. 
   In one embodiment, one can remove the structure from the bath comprising the connecting member, arms and substrates. At least one of the arms can be removed so that plated substrates can be removed from the apparatus, and new substrates can be loaded back into the apparatus. The removable arm can be re-attached to the connecting member, and then the connecting member, arms and substrates can be placed back within the bath so that the new substrates can be plated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  illustrates plating apparatus constructed in accordance with the invention. 
       FIG. 1B  illustrates a structure for holding substrates to be plated within the apparatus of  FIG. 1A . (Details concerning the structure of  FIG. 1B  are not shown in  FIG. 1A  for ease of illustration.) 
       FIG. 2  is a front cross section view of the structure of  FIG. 1B . 
       FIG. 2A  illustrates in cross section the structure of  FIG. 2  taken along lines  2 A- 2 A. 
       FIG. 3  illustrates in cross section the structure of  FIG. 2  taken along lines  3 - 3  comprising a set of gears for imparting planetary motion to substrates during plating. 
       FIG. 4  illustrates in cross section the structure of  FIG. 2  taken along lines  4 - 4  comprising the set of gears for imparting planetary motion to substrates during plating. 
       FIG. 5  illustrates in cross section the structure of  FIG. 2  taken along lines  5 - 5 . 
       FIG. 6  illustrates in cross section the structure of  FIG. 2  taken along lines  6 - 6 . 
       FIG. 7  illustrates the portion of the structure of  FIG. 5  indicated by lines  7 - 7 . 
       FIG. 8  illustrates a portion of the structure of  FIGS. 1B and 2  comprising a set of mandrels for holding substrates, an end plate connected to one end of the mandrels, and a cruciform connected to the other end of the mandrels. 
       FIG. 9  illustrates in plan view an end plate for connecting to the mandrels. 
       FIG. 10  illustrates a mandrel used in the apparatus of the above-mentioned figures for holding substrates during plating. 
   

   DETAILED DESCRIPTION 
     FIGS. 1A and 1B  illustrate apparatus  10  for plating a layer of material onto substrates S ( FIGS. 1B ,  2  and  8 ). Substrates S can be disk-shaped metal substrates (e.g. an aluminum or copper alloy), and the material plated onto the substrate can be a nickel-phosphorus alloy. However, these materials are merely exemplary. In one embodiment, substrates S have a centrally defined opening therein (not shown), but in other embodiments, substrates S do not have such a centrally defined opening. 
   Apparatus  10  includes a bath B containing plating solution and a holder  16  immersed in bath B for holding and moving substrates S. (Only one substrate S is shown in  FIG. 1B , but typically numerous substrates are simultaneously held by holder  16 . The internal structure of holder  16  is not shown in  FIG. 1A  for ease of illustration, but is shown in  FIG. 1B .) 
   As explained below, during plating substrates S are held by a set of mandrels M. (Mandrels M are substantially parallel. Also, substrates S are substantially parallel.) Apparatus  10  comprises a motor  18  which turns a system of gears GL 1 -GL 3  and GLa-GLd for moving mandrels M (and hence substrates S) in a planetary manner during plating. Gears GL 1 -GL 3  and GLa-GLd drive mandrels M from the left side of apparatus  10 . Gears GR 2  and GR 3  (similar to gears GL 2  and GL 3  and shown in  FIGS. 2 and 5 ) drive mandrels M from the right side of apparatus  10 . The mechanical coupling between motor  18  and mandrels M is described below. In one embodiment the motion of substrates S through the plating solution facilitates a) more even plating of material onto the substrate surfaces, b) a more homogenous thickness and surface roughness, and c) greater plating solution velocity across substrates S to remove bubbles and particles to theoretically reduce the number of defects. 
   Another feature of apparatus  10  is that it applies a voltage to substrates S during at least a portion of the plating process via a source of electrical power P, cable  20 , bar  22  (mounted on the outside of left wall WL of holder  16 ), wire  24  ( FIGS. 2 and 6 ), spring-loaded contact pin  26 , metal contact plate  27  (mounted on gear GL 3 , and shown in  FIGS. 2 ,  4  and  6 ), a set of trunions TLa-TLd, cruciforms Ca-Cd and mandrels M. In this way, a “strike voltage” can be applied to substrates S at the start of plating. (The electrical return path is provided via cables  28  and bars  29  (immersed in bath B, shown in  FIG. 1 ).) The strike voltage electrical path is discussed below, following the discussion of the mechanism for driving (moving) the mandrels. 
   Mechanism for Moving Mandrels M and Substrates S During Plating 
   Holder  16  comprises four sets of mandrels M, each set comprising four mandrels for holding a set of substrates S. For example, in  FIG. 1B , one set of mandrels (comprising mandrels Ma 1 , Ma 2 , Ma 3  and Ma 4 ) is shown holding a substrate S. Referring to  FIGS. 1B and 2 , the left end of each set of mandrels is connected to an associated one of cruciforms Ca-Cd and on the right end of each set of mandrels is connected to an associated one of end plates Ea-Ed. (Only two end plates Ea and Ec, two cruciforms Ca and Cc, and four mandrels M are shown in  FIG. 2  because it is a cross section drawing. However, all four end plates Ea-Ed are shown in  FIG. 5 .) 
   Each cruciform Ca-Cd is rigidly connected associated posts PLa-PLd, which in turn are rigidly connected to associated gears GLa-GLd. Posts PLa-PLd are also rotatably coupled to gear GL 3  via trunions TRa-TRd. Each end plate Ea-Ed is rotatably coupled via an associated one of posts PRa-PRd to gear GR 3 . As explained below, gears GLa-GLd, GL 3  and GR 3  are parts of a gear mechanism that moves mandrels M in a planetary manner during plating. The motion of gear GL 3  is synchronized with gear GR 3  to cause mandrels M to revolve about the central axis A 3  ( FIG. 2 ) of gear GL 3  (which is also the central axis of gear GR 3 ). Gear GL 3  drives mandrels M from the left side of holder  16 , while gear GR 3  drives mandrels M from the right side of holder  16 . A description of the mechanism that drives mandrels M from the left side will be provided, followed by a description of the mechanism that drives mandrels M from the right side. 
   A motor  18  drives a rotor shaft  19  which in turn drives first gear GL 1  in a direction DL 1  ( FIG. 3 ), which in turn drives second gear GL 2 , in a direction DL 2  which in turn drives third gear GL 3  in a direction DL 3 . Trunions TLa-TLd are affixed to and extend through associated openings in gear GL 3 . Each one of posts PLa-PLd is rotatably mounted within an associated one of trunions TLa-TLd. Thus, as gear GL 3  rotates about its central axis A 3 , posts PLa-PLd also rotate about axis A 3 . Since posts PLa-PLd are rigidly connected to cruciforms Ca-Cd, respectively, cruciforms Ca-Cd and mandrels M also rotate about axis A 3 . 
   A gear GL 4  is rigidly (non-rotatably) mounted to wall WR of holder  16 . Gears GLa-GLd are each rigidly (non-rotatably) connected to an associated one of posts PLa-PLd. As post PLa rotates about the central axis A 3  of gear GL 3 , gear GLa engages gear GL 4 , thereby causing gear GLa rotate in a direction Da, which in turn causes post PLa, cruciform Ca and the associated set of mandrels Ma 1 -Ma 4  to rotate about the central axis of gear GLa. Thus, not only do mandrels Ma 1 -Ma 4  rotate about central axis A 3  of gear GL 3 , but they also rotate about the central axis of gear GLa. Gears GLb-GLd similarly engage with gear GL 3 , thereby causing posts PLb-d, cruciforms Cb-d, and their associated mandrels M to rotate about the central axis of associated gears GLb-GLd in directions Db-Dd, respectively. 
   Referring back to  FIGS. 1B and 2 , gear GL 2  also drives an idler shaft  30 , which in turn drives gear GR 2 , which in turn drives gear GR 3 . Gear GR 3  is rigidly affixed to a rotating plate  40  ( FIGS. 5 and 7 ) via a post  41 . Posts PRa-PRd, extending from associated end plates Ea-Ed, ride in openings Oa-Od of plate  40 . Thus, as gear GR 3  rotates about axis A 3 , plate  40  and end plates E also rotate about axis A 3 . Gears GL 3  and GR 3  move synchronously, and therefore, both sides of mandrels M are driven synchronously. 
   Posts PRa-PRd rotate freely within openings Oa-Od. There is nothing analogous to gears GLa-GLd on the right side of holder  16 . Thus, in the illustrated embodiment, rotation of mandrels M about the axes of gears GLa-GLd is imparted only from the left side of holder  16  and not from the right side of holder  16 . However, in alternative embodiments, such rotation of mandrels M about the axis of gears GLa-GLd can be imparted from both the left and right sides of holder  16 . Alternatively, in other embodiments, such motion could be imparted from only the right side of holder  16 . Referring to  FIG. 5 , a ring R extends about plate  40 . Ring R is fixedly mounted to a side wall WR of holder  16  via posts  48 , and does not rotate. Thus, plate  40  rotates within ring R. Ring R prevents posts PRa-PRd from disengaging from openings Oa-Od in plate  40  during use. 
   Application of Electrical Power to Substrates S 
   As mentioned above, at the start of plating, a strike voltage is provided by electrical power source P, cable  20 , bar  22 , wire  24 , spring-loaded contact pin  26 , and metal contact plate  27  (mounted on gear GL 3 , and shown in  FIGS. 4 and 6 ). Metal contact plate  27  is electrically coupled to mandrels M via trunions TRa-d, posts PLa-d, and cruciforms Ca-d. (Trunions TRa-d, posts PLa-d and cruciforms Ca-d are electrically conductive and typically made of metal.) 
   Mandrels M typically comprise an electrically conductive stainless steel core MCO ( FIG. 10 ) surrounded by an electrically insulating polyvinyl difluoride coating MI. As each set of mandrels M is affixed to an associated one of metal cruciforms Ca-d, the conductive core MCO of each mandrel M electrically contacts one of cruciforms Ca-d. As seen in  FIGS. 8 and 10 , each mandrel M comprises a set of notches MN for holding substrates S. Notches MN expose conductive core MCO, so that each substrate S electrically contacts core MCO of the mandrels M holding that substrate. In this way, there is an electrical path from power source P to substrates S. 
   Apparatus  10  applies electrical power to substrates S only via the left side of mandrels M. Thus, end plates E are typically not electrically conductive. (The various gears in apparatus  10  are also not typically electrically conductive.) However, in other embodiments of the invention, electrical power can be applied to the right side, or both the right and left side, of mandrels M. 
   One advantage of using cruciforms Ca-Cd in lieu of conductive plates is the minimization of metallic surface area exposed to the plating solution. Similarly, the shape of electrically conductive plate  27  is also designed to minimize the metallic surface area exposed to the plating solution. Similarly, insulting coating MI also minimizes the metallic surface area exposed to the plating solution. 
   Loading and Unloading Substrates from Apparatus  10   
   After plating, one removes holder  16  from bath B. One set of four mandrels M, associated endplate E and cruciform C form a “rack” for holding substrates (see  FIG. 8 ). In one embodiment, each rack typically holds 42 substrates S. Holder  16  is designed so that the racks can be removed therefrom. In particular, an arcuate section Ra of ring R is removed from ring R by removing screws  50   a ,  50   b  ( FIG. 7 ). One removes a rack of substrates from holder  16  by a) rotating the mandrels until one of posts PL is aligned with removed arcuate section Ra. One then lifts the rack (including mandrels M, endplate E and cruciform C) out of holder  16 . One then removes one of the mandrels M as shown in  FIG. 8  by removing screws  52   a ,  52   b  which hold that mandrel in place. Once that mandrel is removed, substrates S can be loaded and/or unloaded from the rack. The mandrel is then replaced, and the rack can then be reinserted into the apparatus. 
   As mentioned above, apparatus of the present invention can be used for a variety of plating processes, including electroless plating and electroplating. In one process, one first soaks substrates S in an alkaline cleaner (e.g. a KOH solution plus an inhibitor), rinses substrates S, soaks substrates S in an acidic solution (e.g. phosphoric acid), again rinses the substrates, and then places the substrates in a first plating bath. This bath comprises the chemicals used to plate NiP, e.g. nickel sulfates, sodium hypophosphite and chelating agents. In one embodiment, the nickel plating chemistry can be type 300 ADP, manufactured by Enthone Corp. (See, for example, the data sheet entitled “ENPLATE ADP-300(QA) Electroless Nickel Process for General Plating Applications” published in 2000 by Enthone-OMI, Inc., incorporated herein by reference, submitted in an Information Disclosure Statement concurrently herewith.) Other plating chemistries are available from OMG Chemistries. A strike voltage of about 3 volts can be applied to the substrates, e.g. for about 15 to 60 seconds, but these parameters are merely exemplary. Thereafter, the substrates can be electrolessly plated in the same bath or a different bath from that used to apply the strike voltage. 
   While the invention has been described with respect to specific embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. For example, in lieu of using stainless steel to conduct electrical current to the substrates, other electrically conductive materials can be used. The disclosed apparatus can be used to plate materials other than NiP onto one or more substrates, and the substrates can comprise a material other than Al alloys or spinodal copper. The apparatus can be used to apply a strike voltage to initiate electroless plating. Alternatively, the apparatus can be used to apply a voltage during electroplating. Instead of using one electrical contact pin  26 , multiple pins could be used. Alternatively, a brush, strip or ribbon contact could be used. 
   In lieu of using contact pin  26 , in another embodiment, gear GL 3  is mounted on and rotates about an electrically conductive bearing coupled by an electrically conductive post and bolt to wall WL of holding structure  16 . In such an embodiment, wire  24  is connected to the portion of that bolt on the right side of wall WR. The conductive bearing is electrically connected to plate  27 . 
   Some of the gears in the drawings have been illustrated as having different thicknesses. In alternative embodiments of the invention, the various gears have the same thickness. 
   In lieu of using cylindrical mandrels M, other types of holding members can be used to hold substrates S. For example, the mandrels can have the shape of arcuate sections of a cylinder. (As used herein, the term mandrel is not limited to a cylindrical mandrel. The term “arms” includes mandrels.) Different numbers of mandrels (other than four) can be used in each rack of substrates, and holder  16  can be designed to accommodate different numbers of racks (other than four). It is not necessary that all of mandrels M be electrically conductive. Also, it is not necessary that the entirety of cruciforms C be electrically conductive. Instead of using bar  22  and wire  24  to connect to pin  26 , cable  20  can be connected directly to pin  26 . Instead of placing all of bars  29  on one side of bath B, bars  29  can be arranged at different locations within bath B. Further, in lieu of bars  29 , one could use a panel, grid, or any other shape of conductive material near the substrates. In another embodiment, gear GL 3  is replaced with a wheel, and a pulley can connect rotor  19  to the wheel to rotate the mandrels. 
   Instead of using the above-mentioned chemicals to plate NiP, other chemicals can be used. Further, the apparatus can be used to provide a plated layer of materials other than NiP. 
   A method and apparatus in accordance with the invention can be used to make masters or stampers, e.g. as discussed in the above-incorporated &#39;380 application. Alternatively, one can use the method and apparatus to plate other types of substrates, e.g. to make magnetic disks or structures on semiconductor wafers. 
   Some embodiments of the invention employ one or more aspects and advantages of the above-described apparatus and method without employing other aspects and advantages. Accordingly, all such modifications come within the present invention.