Whisker Growth On Tin Substrates

1
Whisker Growth On Tin Substrates

• Key Paper Presentation
• Winnie Lee
• February 15, 2002
• Advisor Dr. Guna Selvaduray

2
Outline of Presentation

• Introduction
• Experimental Method
• Results
• Evaluation of Results
• Discussion of Experimental Methodology
• Analysis of Results
• Relation to My Work

3
Introduction

• Conference Proceeding
• 4th International SAMPE Electronics Conference (
  June 12-14, 1980)
• Tin Whiskers Mechanism of Growth and
  Prevention by Kathleen M. Cunningham and Michael
  P. Donahue
• Affiliated with Raytheon Company Missile Systems
  Laboratories

4
Introduction (Motivation For Study)

• Tin coatings offer many excellent properties
• Tin whiskers can grow from tin coatings and
  platings
• May cause electrical failures in working devices
• Affect product reliability and service life

5
Experimental Method

• Samples
• - 6061 Aluminum QQ-A-250 as base material
• - Copper underplating
• 4 different plating systems
• Pure tin electroplate
• Hot tin dip coating
• 90 Sn-10Pb solder plating
• 60 Sn-40 Pb solder plating with hot oil reflow

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Experimental Method(Contd)

• Samples were assembled on a test module unit
• Unit was exposed at a temperature of 93C
• A torque of 72.13 meters-grams was applied on
  unit
• Electrical testing done on unit
• If electrical short was recorded, unit was
  disassembled to check for tin whiskers

7
Results of Testing

• Optical microscope and SEM were used
• 2 types of whiskers found nodular filament
• Whiskers formed ridge and cluster
• Whiskers found in areas where mechanical stresses
  were applied
• No whiskers found on 60Sn-40Pb plating with hot
  oil reflow

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(A) Discussion On Method

• Plating systems satisfied basic criteria for tin
  plating replacements
• Temperature and torque were chosen respectively
  as they yield highest density of whiskers
• Electrical testing was a good approach to check
  for presence of whiskers

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(A) Discussion On Method(Contd)

• Unit was only disassembled when electrical short
  was recorded
• - Whiskers do not always cause shorts
• One more test unit should be included
• - An additional set of parameters available
• Time interval between testing of samples is
  unknown

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(B) Analysis Of Results

• Results obtained were pertinent to study
• Highest density of whisker growth discovered
• Types of whiskers were found
• Time taken for electrical short to occur was
  recorded
• Correlation between mechanical stress, heat and
  whisker growth

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Relation To My Work

• Goals of my project Determine driving force(s)
  and growth mechanism of tin whiskers
• Tin dip coating of copper samples
• Application of mechanical stresses and exposure
  to elevated temperatures
• Positive results yielded!!

12
Conclusion

• Study related to my work
• Results are positive
• Alternative methodology discovered