Nickel-Palladium Based Component Terminal Finishes I

Erroneous perceptions such as high cost driven by Pd content and price, quality problems at board mounting, and package reliability limits MSL(Moisture Sensitivity Level) have led some IC component suppliers to reject adopting or even evaluating NiPd based PPFs.

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Idea Information

Background: 

Matte tin (Sn) is being favorably viewed as a lead (Pb)-free finish for integrated circuit (IC) component terminations, despite the risk of Sn-whiskers. The electronics industry has chosen matte Sn plating because of the simple transition from SnPb post-mold plating and the assumed low cost of Sn finishes. Various mitigation / amelioration techniques have been proposed to reduce the Sn-whisker risk with matte Sn finishes.  Nevertheless, most end users of electronic components (system integrators and EMS providers) still have concerns about long term Sn-whisker growth risk with Sn based termination finishes. NiPd based Pre-Plated lead Frame (PPF) finishes have been introduced as one Pb-free alternative with no Sn-whisker risk.

NiPdAu and NiPdAu-alloy are Pb-free finishes for component leads with total cost of ownership advantages over post mold plated finishes such as matte Sn and SnPb and with no risk of Sn-whiskers. PPF means that the solderable finish on the lead is applied at the leadframe maker, prior to IC assembly, which eliminates the need for post-mold plating.

Problem: 

Erroneous perceptions such as high cost driven by Pd content and price, quality problems at board mounting, and package reliability limits MSL(Moisture Sensitivity Level) have led some IC component suppliers to reject adopting or even evaluating NiPd based PPFs.

These perceptions have their basis in :

  • Pd is a precious metal with a current price of ~ $200/toz. Leadframe suppliers have addressed this by  developing versions of NiPd based PPF finishes, such as the NiPdAu and NiPdAu-alloy, that reduce Pd content by ~85% over prior versions. 
  • Thin Pd (0.005 - 0.015µm vs. 0.075 – 0.15µm thickness formerly) was developed to address wetting balance solderability performance [2,4,5,7]. 
  • Moisture sensitivity levels of NiPd based PPF are now on a par with those of Sn and SnPb post mold finished components at 260°C Pb-free reflow conditions with green mold compounds.

Definition Information

Approach: 

Conclusions:

  • NiPd based PPF’s are economical and effective Pb-free finishes for IC leads (terminations).
     There is no risk of Sn whiskers with NiPd PPF.
  • There are tens of billions IC’s in use with NiPd base PPF finished leads that have been sold over the past 15 years.
  • One key issue, cost of the NiPd based leadframe finish, has been addressed by reducing the Pd content by ~7X and adding an ultra thin (30~100 angstrom) top layer of Au. 
  • Newer versions of NiPd base PPF showed an additional functional quality improvement, using alloy 42 base metal leadframes and MSL improvement against higher reflow temperature for Pb-free surface mounting and similar shapes of side wetting performances.
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