Technical Paper

Palladium Alloy Hardening and Wear Away Characteristics

Prepared by Takuto Yoshida / Craig Hudson.

Presented at BiTS Workshop on March 9 - 12, 2014

 

Introduction to Pd Alloy

  • Palladium (Pd) alloy is a common option for spring pin plunger creation.
  • The primary demerit of using Pd alloy is the finished plunger cost; so to offset this demerit, Pd alloy should be deployed only when appropriate.
  • Pd alloy’s primary merit for IC testing is the alloy’s hardness, helpful in preventing solder migration to the spring pin’s plunger tip.
  • The primary targeted results for deploying Pd alloy plungers are:
    • Reduced variability of Cres over life of pin
    • Improvement of pin tip longevity
    • Throughput improvement by less frequent cleaning

But how does the hardness of the Pd alloy impact wear away?

Precipitation Hardening Process

Steps:

  • Pre-heat the hardening chamber
  • Insert the parts into the hardening chamber for heat treatment in nitrogen
  • Cool down in nitrogen

Hardness Measurement Process

Steps:

  • The sample is encased in epoxy
  • A grinder and polisher are used to remove the material until a cross section is revealed
  • Measure hardness by  Vickers hardness tester

Hardness vs. Heat Treatment Temperature by Supplier

Breaking Force by Bending Test

  • For the breaking force, we are using a three point bending test (flexural) method
  • Reading is recorded once the material breaks 
  • Breaking counts are recorded

Breaking Force and Heat Treatment Temperature

Plunger Tip Wearing by Cycling Test

  • Sample pin
    • Hardest plunger and moderate hardness plunger
    • Single ended pin for 0.35mm pitch
    • Spring force is 28gf
  • Cycle test
    • Two kind of pin insert into same socket
    • Cycle test until 200K 
    • Golden plated flat dummy device
    • Measure Plunger Flat Ratio every 25K cycle

 

Definition of Plunger Flat Ratio

Plunger Tip Wearing

Plunger Tip Wearing After 200k Cycle

Summary

  • Pd alloy material hardness and heat treatment condition
    • The heat treatment temperature are different by supplier
    • The hardest value are different by supplier
  • Pd alloy material bending characteristics
    • The hardest sample breaks minimum bending force
    • Higher heat treatment temperature introduce higher braking ratio
  • Pd alloy material wear away characteristics
    • Hardest plunger average Plunger Flat Ratio (wearing) is smaller than moderate plunger
    • Hardest plunger wearing variation is wider than moderate plunger
    • Hardest plunger wearing is worse than moderate plunger
  • Moderate hardness Pd alloy material is the best for the plunger