Abstract:
Plating rack for releasably holding parts in a plating process, as well as processes for fabricating and using such a rack, including spring members mounted to a frame which releasably hold plate-shaped parts from the opposite side edges of the parts in a manner permitting the part to move sufficiently, without disengagement, when immersed in an agitated plating fluid such that plating occurs on all the exterior surface regions of the plate and scarring is avoided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional application serial No. 60/268,864, filed Feb. 16, 2001, the entire disclosure and contents of which are incorporated herein by reference for all purposes. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention generally relates to a plating rack and more particularly to a plating rack used for releasably holding parts in a plating process, as well as processes for fabricating and using such a rack.  
         BACKGROUND OF THE INVENTION  
         [0003]    Work holding fixtures, also often referred to as plating racks, have been used for temporarily holding a plate-shaped part or workpiece during an immersion electroplating operation, and the handling associated with loading and unloading the part from the plating tank. Unfortunately, previous rack plating fixtures arrangements and techniques have retained the part during plating in a manner leaving a plating defect in the form of a “scar” of unplated surface area on the part. This “scarring” defect occurs where the retention device physically contacts the part throughout the duration of the plating procedure. Consequently, such prior retention systems blinded and masked a portion of the peripheral side edges, and/or major surface regions of the part adjoining the side edges, from the plating solution. Those surface regions of the plate were left bare and unplated. The plating defect can be problematic. Some high precision microelectronic parts or related support parts, for instance, may not meet performance requirements, tolerances and/or specifications if such unplated “scars” are formed on the plated part, even in the case where such defects are restricted to the peripheral side edges of the part.  
         SUMMARY OF THE INVENTION  
         [0004]    The above problems and shortcomings are solved by the present invention in which a plating rack holds plate-shaped parts or workpieces in a plating process with retaining means permitting all exterior surface areas of the part to be completely covered by plating material. Advantageously, the plating rack of the present invention does not leave plating defects, such as scars or witness marks of the retaining device, in the plated part.  
           [0005]    In one aspect, the plating rack includes a unique fixturing arrangement well-suited for use in plating procedures in which relatively predictable relative movement between parts and the plating solution in the plating tank is created during the plating procedure. The plating rack is lowered into a plating tank sufficient that the fixtured part(s) is immersed in the plating fluid. To create the relative movement between the part and plating fluids, the part can be plated in a plating process involving turbulence created in the plating fluid. This turbulence can be created in a variety of manners, such as by sparging of gas into the working fluid in the plating tank, and the like; and/or by mechanical agitating or stirring the working fluid, and the like; and/or by constant flow movement of the working fluid in the plating tank due to continuous circulation of the working fluid, such as an electrolyte solution for electroplating, out of and back into the plating tank using pumping action for additional purposes of filtering and/or replenishment of the working fluid, and the like. The terms “plating fluid” and “working fluid” are generally synonymous for purposes herein.  
           [0006]    In general, the plating fluid can be an electroplating fluid or an electroless plating fluid.  
           [0007]    In one aspect of the present invention, there is a plating rack including a frame having brackets in-between which plate-shaped parts are retained during a plating procedure, from opposite side edges thereof, using certain spring members as fixturing devices. The spring members each are fixedly attached at one end to a bracket and the opposite free end is spring biased toward a nearest side edge of the part. The free or distal end of each spring member includes a curved portion having inner surface defining a notch such that the curved portion makes points of contact with the part that is limited to the pair of right angle edges, i.e., the edge corners, of the side edges of the part. The corners of the part are formed where the major surfaces thereof intersect with the side edges arranged generally at approximately right angles thereto.  
           [0008]    The significance of this configuration is that the spring force provided by the spring members, also referred to herein occasionally as spring arms, is sufficiently matched to the agitation/turbulence/fluid motion in the plating solution such that plating occurs all over the plate. That is, the turbulence in the electroplating bath causes the part to move around within the notch of the spring retention device sufficiently to ultimately expose all the exterior surfaces of the part to contact with the plating fluid, while retaining the part sufficiently such that the part does not become inadvertently disengaged from the spring arm and fall off the rack into the plating tank. The spring tension is thus set in advance to provide a minimal force needed to retain the part by the spring arms assigned to that part for the duration of the plating procedure and associated handling, while leaving enough “play” in the retentive force between the spring arm notches and the corners of the part such that turbulence in the plating bath can create circulation of the plating fluid over the entire side edge surfaces as the spring notch moves to-and-fro and laterally relative to the plate edges due to the turbulence in the working fluid in the electroplating tank. The retention system is configured such that the amount of lateral movement permitted and tolerated does not permit the spring member to become disengaged from the part. In this way, the spring force of the spring retention devices against side edges of the part and the surface forces created by the movement induced in the plating fluid against the part surfaces are balanced such that the plating fluid can flow and circulate over all exposed surfaces of the plate. In addition, the spring arms also retain the plate on the plating rack during loading and unloading transfer of the plating rack before and after, respectively, conducting the electroplating procedure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Other features, objects, and advantages of the present invention will become apparent from the following additional description of the invention with reference to the drawings, in which:  
         [0010]    [0010]FIG. 1 is a frontal view of a plating rack including fixtured parts to be plated according to an embodiment of the invention;  
         [0011]    [0011]FIG. 2 is a side view of the plating rack shown in FIG. 1;  
         [0012]    [0012]FIG. 3 is an isolated enlarged side view of region “B” indicated in FIG. 2, including a part in a retained position using spring arms according to an embodiment of the invention;  
         [0013]    [0013]FIG. 4 is an isolated perspective view of a spring arm used to retain parts being plated according to embodiments of the invention.  
         [0014]    [0014]FIG. 5 is an isolated frontal view of a part in the retained position with spring arms according to another embodiment of the invention, where spring arms extend at angles from shared attachment means on the frame brackets to engage and retain opposite sides of the part to be plated;  
         [0015]    [0015]FIG. 6 is an isolated, enlarged side view of a part to be plated in the retained position within the notch of a spring arm according to the invention including indication of slight relative to-and-fro (rocking) motion induced as between the plate and the spring arm, such as by plating bath turbulence;  
         [0016]    [0016]FIG. 7 is an isolated side view of a spring arm with its structural dimensions and geometries shown and indicated according to one preferred embodiment of the invention; and  
         [0017]    [0017]FIGS. 8A and 8B show steps of an exemplary procedure for racking (retaining) parts according to an embodiment of the invention. 
     
    
       [0018]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Similar numbered features in different figures represent similar parts unless indicated otherwise below.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    The present invention relates to a plating rack for holding plate-shaped parts or workpieces in a plating process with retaining means permitting all exterior surface areas of the part to be completely covered by plating material. The plating rack of the present invention does not leave plating defects, such as scars or witness marks of the retaining device, in the plated part. The terminology “plate-shaped”, as used herein, generally refers to an overall shape of a discrete object having relatively flat major surfaces on opposite sides thereof, and length and width dimensions of the major surfaces are substantially greater in magnitude than the thickness dimension of the object as measured between the major surfaces.  
         [0020]    While the detailed discussion of the invention provided herein may illustrate the invention by way of the processing of a single plate-shaped part or the structure or nature of a given spring member, it will be appreciated that the invention encompasses use of a plurality of spring members to retain each part to be plated, and that invention contemplates using its precepts for plating a single part or a plurality of parts simultaneously.  
         [0021]    Referring now to FIG. 1, a plating rack  10  includes a frame  10  comprising a series of brackets  12   a - 12   j,  and the neighboring pairs of which are spaced-apart a uniform equal distance “m” between their midlines. Plate-shaped parts  13   a - 13   e , and so forth, are retained during a plating procedure from opposite side edges thereof using spring members  14   a - 14   d , and so forth, as fixturing devices.  
         [0022]    In one preferred embodiment, the spring members  14   a - 14   d  are integral double-armed spring wire structures, as discussed in more detail below, that are connected to the brackets at a medial portion of the spring members. In that way, spring members  14   a,    14   b,  and so forth, can support retention of parts located on both sides of a bracket. As illustrated in FIG. 1, the spring members  14   a - 14   d  preferably are oriented generally at right angles (90°) relative to the nearest sides of the part  13   a  being retained.  
         [0023]    As shown in FIG. 2, the loaded plating rack  10  is shown as immersed into a plating fluid bath  23  in a vertical orientation and maintained at that position by a hook  22  provided at the top of the frame  11 , which is hooked over a stationary bus bar  21 . In this way, means is provided for removably loading the plating rack  10  into a plating tank or container.  
         [0024]    Referring to FIG. 3, each spring member  14   a - 14   d , and so forth, used to retain a part for plating, are fixedly attached at one end  14   e  to a bracket. For instance, spring member  14   a  is attached to bracket  12   b  by attachment means  15 , which, for example, can be a threaded bolt  15   a  and washer  15   b.  The bracket includes through-holes for receiving the bolts  15 , and the bolts have flanges at one end that clamp a portion of the spring member against the bracket, such as at an intermediate crimped or looped portion  14   j  of the spring member  14   a  (best seen in FIG. 4). Then, the bolt is fastened to the bracket via the washer on the opposite side of the bracket to clamp a portion or end of the spring member to the bracket. The free end  14   f  of the spring member  14   a  includes a portion  14   g  which is spring biased toward a nearest side edge  13   f  of the part  13   a.  The spring biased portion  14   g  includes a curved inner surface  14   h  defining a notch  14   i  such that the curved inner surface  14   h  makes contact and bears against the part  13   a.  In particular, the curved inner surface  14   h  makes varying points of contact with the side edge  13   f  of the part  13   a  where the points of contact are limited to the edge corners where the side edges meet the major faces of the part. Spring member  14   d  similarly bears against the opposite side edge  13   g  of part  13   a.    
         [0025]    In another embodiment of the invention illustrated in FIG. 5, four discrete spring members  140   a - 140   d  are attached in pairs at common attachment means  150 B and  150 A located on the respective brackets  120   b  and  120   a.  In one preferred embodiment, spring arm members  140   a - 140   d  are single-armed wire structures. The spring members are attached at an angle “p” to the nearest side edge of the part  130   a.  The angle “p”, for example, can be any angle at which the retention of the part  130   a  is still maintained, such as where “p” is about 50 to about 130° (including 90°), while also permitting adjoining spring members to share an attachment means (e.g., see features  150 A,  150 B). By comparison, the arrangement shown in FIG. 2 has laterally-neighboring spring members  14   a  and  14   b  being bolted separately to the same bracket  12   b.    
         [0026]    In one aspect, each of spring members  140   a - 140   d  comprise a partial version of the spring member shown in FIG. 4 such that spring member comprises only the structure below line  14   k.  The crimped or looped intermediate area  14   j  provided in each of spring arms  140   a - 140   d  is included and is fastenable to a bracket using attachment means  150 A or  150 B.  
         [0027]    Phantom lines included in FIG. 5 indicate possible separate spring members that extend from the attachment means towards the next set of brackets (not shown) located above and below brackets  120   b,    120   a,  for holding additional parts in the rack array.  
         [0028]    With reference now to FIG. 6, turbulence created in an electroplating bath, or other suitable plating bath for the parts, causes the part  130   a  to move along points of contact made between the inner curved surface  14   h  of the notch in spring arm  14   d  and the corners  130   h  and  130   i  of part  130   a.  The corners  130   h  and  130   i  are where the side edge  130   f  of part  130   a  meets at right angles with the opposing major faces  130   j  and  130   k  of the part  130   a.    
         [0029]    The part movement made at the points of contact limited to the corners of part  130   a  occur in a limited predictable fashion within the respective retention notches  14   i  of the spring member  140   a,  and so forth, dedicated to each respective part to be plated. This movement occurs as a to-and-fro or rocking motion on the part corners, as indicated by the double arrow in FIG. 6. Also, the movement also involves slight relative lateral motion induced as between the part  130   a  and spring arm members by the plating bath turbulence, such as indicated in FIG. 5.  
         [0030]    Referring again to FIG. 6, the other depicted spring member  140   e  shown can form part of a double armed spring member, such as described in connection with FIG. 4, or, alternatively, it could be a separate discrete spring member joined to a common bracket with spring member  140   a  using a common attachment means, such as described in connection with FIG. 5.  
         [0031]    The limited to-and-fro and lateral movement, or “play,” provided at the notched portions of the spring arms described herein is sufficient to permit the plating fluid to flow and circulate over all the exterior surfaces of the plate to permit uniform complete plating to be provided without leaving scars, while still retaining the part sufficiently such that the part, or parts, being plated does not become inadvertently disengaged from the spring arm member and fall off the rack into the electroplating tank.  
         [0032]    In designing the spring arm members to provide the aforementioned dual retention/play functionality needed, the spring force needed is determined empirically for a given set of expected or specified plating conditions and that information is matched to the agitation/turbulence that will be encountered by the part during the electroplating procedure. By knowing the relative dimensions of the part to be plated, the bracket spacing, the plating conditions, and the general geometry of the spring arms to be used, one of ordinary skill in the art can determine by empirical experimentation in an electroplating tank the appropriate spring material, size and geometric specifics to attain the dual functionality needed.  
         [0033]    For instance, as discussed above, each spring arm to be used has one end to be fixed at a cross bracket of the rack, and one free end including first major turn or loop (see FIG. 6, feature  14   m ), to create bias toward the part or workpiece, as applicable thereto through the notch ( 14   i ) located closer to the distal end ( 14   f ), as shown in several of the included figures). The spring arms generally are comprised of a discrete elongated piece of wire or rod (preferably circular in cross section) having a general geometry along the length thereof as mentioned above. In one embodiment, a series of different test rods or wires of various types and gauges of steel wire can be tested at a given loop dimension (imparted by mandrel for example) to check by trial and error whether the aforementioned dual functionality in the retention behavior is attained. During this regimen, refinements in the spring bias force of the spring arms, if necessary, after creating the loop via mandrel, can be manually induced by longitudinally extending or compressing the loop in the spring arm (e.g., longitudinally extending the loop to reduce the bias force).  
         [0034]    Once the appropriate spring arm geometry and size is identified and confirmed in this manner, electroplating production runs can be run using those springs members under the conditions used in the trials.  
         [0035]    After being put into service, further adjustments in the spring bias force of the spring arms can be made, if necessary, e.g., to offset any spring memory fatigue effects, by manually inducing longitudinal extension or compression of the loop in the spring arm (e.g., longitudinally compressing the loop to increase the bias force).  
         [0036]    In one implementation, mentioned above, the spring arms are provided as a pairing in a one-piece assembly fixedly attached to the bracket at the middle of the assembly, so that the pairing of springs engages a common side of a part, as shown in several of the figures. Alternatively, each spring member or arm can be a separate member attached to a bracket along with other separate springs by a common attachment means (e.g., a bolt). One, two or more spring members could be used at a time to engage a side of the part. Generally, a symmetry in spring members should be deployed over opposite side edges of a common part.  
         [0037]    The plate-shaped part to be plated using this invention includes side edges having a uniform thickness along the length of at least the top and bottom sides, and preferably all around the part. The bulk of the part generally has a uniform thickness, although some contour spaced from the edges can be included, such as to form lid seats if the part is a lid. The part generally has top and bottom side edges extending parallel to each other. The part can have any profile meeting these criteria and usually is a discrete rectangular-shaped wafer or slab of material.  
         [0038]    To create the relative movement between the part and plating fluids, the part can be plated in a electroplating process involving turbulence created in the plating fluid by by sparging of gas into the plating fluids in the plating tank, and the like; and/or by mechanical agitation or stirring means immersed in the working fluid, and the like; and/or due to constant flow movement of the working fluid caused by continuous circulation of the electrolyte solution out and back into the plating tank by pumping such as for additional purposes of filtering and replenishment, and the like. In a preferred embodiment, the relative movement between the part and working fluid is created by sparging of gas (e.g., air) conducted at a location in the tank fluids below the loaded plating racks in combination with the constant flow movement of the working fluid caused by continuous circulation of the electrolyte solution (i.e., the working fluid) out and back into the plating tank via manifolds in the tank walls using pumps.  
         [0039]    Turbulent electroplating systems using mechanical agitation means are described, for example, in U.S. Pat. No. 4,686,014, which teachings are incorporated herein by reference. Again, the plating racks of this invention generally contemplate applicability in plating procedures, such as electroplating procedures, involving agitation or stirring and the like of the electrolyte or other applicable plating solution in the tank.  
       EXAMPLE  
       [0040]    A non-limiting, illustrative example of a suitable plating frame and a spring arm construction, are as follows.  
         [0041]    Spring (arm) member:  
         [0042]    The spring arm material can be, for example, tempered, stress-relieved stainless spring steel, such as 302 or 304 stainless steel. As one non-limiting illustration, the spring arm diameter is 0.030 inch; the steel has an ASTM A313 tensile strength of 250-325 KPSI; the spring arm loop (see FIG. 6, feature  14   m ) has a loop radius of a 0.25 inch mandrel. The spring arm retention notch  14   i  has a radius of curvature imparted effective to make point contact at each of two corner edges of the part to be plated (top or bottom as applicable); used with an air vise.  
         [0043]    [0043]FIG. 7 shows a spring member ( 14   a,    14   e ) according to one preferred, non-limiting embodiment having dimensions providing the appropriate biasing forces and part retaining functionality described herein for that component. For this non-limiting illustrative embodiment, Y is an angle of 110°, X is an angle of 40°, Z is an angle of 79°, U is an angle of 29°, the dimension “a” is 1.930 inches (49.0 mm), and the radius of curvature R is 0.140 mm. The radius of curvature of the intermediary loop or crimp  14   j  can vary depending, for example, on the size of bolt attachment means.  
         [0044]    Frame:  
         [0045]    The frame material can be stainless steel, such as 302 or 304 stainless steel, or other material resistant to corrosion or chemical attack from the plating fluid. The attachment means for fixing the spring arm to the frame can be threaded steel bolt used with a counter-threaded washer used on backside of the bracket.  
         [0046]    Part(s) for Plating:  
         [0047]    A part to be plated having a thickness as small as approximately 0.125 inch or even less can be releasably retained by the inventive plating rack and spring fixtures components thereof described herein.  
         [0048]    Racking and Unracking of Plating Parts:  
         [0049]    Referring to FIGS. 8A and 8B, steps of a method are shown for racking parts using a plating rack in accordance with one aspect of the invention. In FIG. 8A, the spring members  140   a - 140   d , and so forth, needed to retain parts to be plated have been attached to brackets  120  and  120   b  using bolts  150 A and  150 B. As one non-limiting example, to install parts on the attached spring members, such as shown in FIG. 8B, the bottom of each part  130   a  and  130   b,  and so forth, is tilted backwards relative to the top of the part such that the side edge of the part at the bottom can be placed in the upward facing notches of the spring members located immediately below the part. Then the top of the part is tilted back until guided into the downward facing notches of the spring members located immediately above the part. To unrack the parts after completing a plating procedure, for example, the rack is removed from the plating tank and the rack of plated parts is set down horizontally on a flat surface or tray, which preferably is lined with clean plastic. The rack preferably is positioned on the flat surface such that the curves of the spring members face upward. To release the parts, from the spring members, the parts can be gently pressed downward relative to one set of gripping spring members, such as manually or mechanically, until the spring members release from the opposite set of gripping spring members.  
         [0050]    In one exemplary implementation, the plated racks of the present invention can be used in the fabrication of nickel-plated copper heat sink parts for microelectronic parts to ensure the parts are uniformly and completely plated on every exposed surface, including the side edge faces. This preferably, but not exclusively, is an electroplating procedure.  
         [0051]    While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.  
         [0052]    For instance, while this invention has been illustrated as being applicable to fixturing parts for electroplating processes, it will be understood that the plating rack of the invention also has usefulness in other types of plate coating processes involving turbulent/agitated/stirred plating fluids.  
         [0053]    Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. As used herein, the terms “comprises,” “comprising,” “includes”, “including”, “having”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.