What controls are in place to prevent whisker growth?
Whisker growth is believed to result from stress imparted to the tin layer. Electroplated stress is linked to high plating currents & rapid electroplating process. RCDs electroplating processes are optimized accordingly. In addition, RCD utilizes tight controls on tin purity and plating thickness, and achieves good match of CTE when electroplating Tin (Sn) onto Nickel (Ni) or Copper (Cu). The process of preconditioning the tin plating (heating and cooling) relaxes the molecular lattice structure eliminating stress. Heres a summary of the controls utilized on RCDs MC series of chip resistors to prevent whiskering- 1. Matte Sn finish 2. Heavy Ni barrier thickness 3. A precisely controlled plating process for: a. plating bath parameters: current density, voltage, acidity, b. plating bath chemistry and material contamination c. plating thickness d. plating stress e. plating grain size (large grains reduce whiskering) f. plating crystallographic texture (well polygonized) g. plating carbon
