Process and apparatus for selective passivation of electroless nickel activation or nucleation sites

Abstract

A process and apparatus that enable selective passivation of electroless nickel to control formation and growth of undesired nickel plating between traces without inhibiting plating on the required features is provided. In some embodiments activity of a passivating agent is increased. In some embodiments, activity is increased by agitation using one or more eductors to increase fluid flow velocity of the passivating agent near to introduction into plating bath. One or more baffles can confine the mass-transfer zone. The process and apparatus are also particularly applicable where voltage is not able to control nodule formation, such as in electroless nickel plating.

We claim: 
     
         1 . A process for plating of electroless nickel, the process providing selective passivation of electroless nickel nucleation sites to control formation and growth of undesired nickel plating between traces without inhibiting plating on required features. 
     
     
         2 . A process of controlling nucleation site formation during which a metal is plated upon a substrate in a bath comprising:
 providing a plating bath in which a passivating agent is included in the bath; and   increasing activity of the passivating agent on unwanted nucleation sites by increasing the rate of mass-transfer of the passivating agent on the unwanted nucleation sites.   
     
     
         3 . The process according to  claim 2 , wherein the plating bath is a bath for electroless plating of nickel and the passivating agent is at least one selected from the group consisting of bismuth, lead and antimony. 
     
     
         4 . The process according to  claim 2 , wherein the step of increasing activity of the passivating agent comprises increasing the fluid velocity of the passivating agent containing fluid within a limited region. 
     
     
         5 . The process according to  claim 4  wherein the region of passivation is accomplished within the limited zone, the limited zone formed by a baffle extending into the bath. 
     
     
         6 . The process according to  claim 3 , wherein the plating bath further comprises a hypophosphite. 
     
     
         7 . The process according to  claim 5 , wherein the plating bath downstream of the baffle is not agitated. 
     
     
         8 . The process according to  claim 4 , further comprising the step of moving a web carrying a plurality of substrates to be plated through the plating bath. 
     
     
         9 . The process according to  claim 8 , wherein the substrates comprise copper. 
     
     
         10 . The process of  claim 8 , wherein the step of increasing the activity of the passivating agent is performed near an entry of the web into the bath. 
     
     
         11 . An apparatus for selective passivation during an electroless nickel plating process, the apparatus comprising:
 a plating cell for confining a plating bath therein;   the apparatus further comprising at least one eductor for increasing fluid flow of a passivating agent in the plating bath;   the apparatus further comprising a baffle to confine the increased fluid flow of the passivating agent to only a portion of the plating bath.   
     
     
         12 . The apparatus of  claim 11 , wherein the at least one eductor comprise a series of openings which act as nozzles to increase the fluid flow velocity of the plating bath. 
     
     
         13 . The apparatus of  claim 11 , wherein the at least one eductor is positioned in the plating cell near the entry point of a web entering the plating cell. 
     
     
         14 . The apparatus of  claim 12 , further comprising one or more sensors downstream of the baffle. 
     
     
         15 . The apparatus of  claim 13 , further comprising a roller to move the web through the plating cell. 
     
     
         16 . A process for selective passivation of features on a substrate during an electroless nickel plating process, the process comprising:
 providing a plating bath in which bismuth is included in the bath as a passivating agent;   increasing the activity of the bismuth such that nucleation sites of extra or superfluous plating formation are selectively passivated without preventing plating of desired features on the substrate by increasing the mass-transfer of the bismuth on the nucleation sites.   
     
     
         17 . The process of  claim 16 , wherein increasing the mass-transfer of the bismuth on the nucleation sites comprises agitating the plating bath. 
     
     
         18 . The process of  claim 16 , wherein increasing the mass-transfer of the bismuth on the nucleation sites comprises exposing the nucleation sites to increased concentration of bismuth for a select time. 
     
     
         19 . The process of  claim 16 , wherein increasing the mass-transfer of the bismuth on the nucleation sites comprises increasing temperature of the plating bath. 
     
     
         20 . The process of  claim 16 , wherein the step of agitating the bath comprises passing the bath through one or more eductors. 
     
     
         21 . The process according to  claim 16 , wherein the step of agitating the bath comprises passing a portion of the bath through a series of openings which increase the fluid flow velocity of the bath impinging the bismuth on nucleation sites to passivate the nucleation sites to prevent formation of extra or superfluous plating. 
     
     
         22 . The process of  claim 16 , further comprising limiting the step of mass-transfer of the bismuth by confining the agitating of the bath with a baffle. 
     
     
         23 . The process of  claim 16 , wherein the bath further comprises hypophosphite.