Research Papers

Adhesion and Puncture Strength of Polyurethane Coating Used to Mitigate Tin Whisker Growth

[+] Author and Article Information
Kenny Mahan, Yong Sun, Sungwon Han, Mike Osterman

Mechanical Engineering Department,
Center for Life Cycle Engineering,
University of Maryland,
College Park, MD 20742

Bongtae Han

Fellow ASME
Mechanical Engineering Department,
Center for Life Cycle Engineering,
University of Maryland,
College Park, MD 20742
e-mail: bthan@umd.edu

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 7, 2013; final manuscript received February 17, 2014; published online May 5, 2014. Assoc. Editor: Susan Lu.

J. Electron. Packag 136(3), 031004 (May 05, 2014) (7 pages) Paper No: EP-13-1084; doi: 10.1115/1.4026922 History: Received August 07, 2013; Revised February 17, 2014

Reliability of conformal coatings used to mitigate tin whisker growth depends on their ability to contain tin whiskers. Two key material properties required to assess the reliability of a polyurethane coating are documented experimentally: adhesion strength and puncture strength. A modified blister test using a predefined blister area is employed to assess the adhesion strength and a puncture test is employed to evaluate the puncture strength of the coating. After measuring the properties at time zero, the coatings are subjected to accelerated testing conditions (high temperature/humidity storage and temperature cycling) and the degradations of the coating properties are documented.

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Fig. 1

Schematic illustration of a modified blister test specimen

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Fig. 2

3D view of (a) copper substrate and (b) copper plug mold

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Fig. 3

Copper substrate with epoxy plugs

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Fig. 4

Schematic cross sectional view of sample preparation process: (a) tin plated substrate and plug mold, (b) temporary mask and release agent application, (c) temporary shim for conformal coating curing, and (d) final blister test specimen

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Fig. 5

Schematic diagram of the blister test setup

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Fig. 6

Blister test setup

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Fig. 7

Schematic diagram of the puncture test setup

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Fig. 8

Puncture test setup

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Fig. 9

Typical pressure versus blister height results for the blister test of a polyurethane conformal coating before aging

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Fig. 10

Nonlinear regression results of the elastoplastic curve to determine the hardening constant and yield strength of the coating

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Fig. 11

Adhesion strength versus hours in a T/H chamber

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Fig. 12

Adhesion strength versus cycles in a T/C chamber

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Fig. 13

Typical load versus deflection results for the puncture test of a polyurethane conformal coating

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Fig. 16

Puncture force and buckling force versus whisker length

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Fig. 17

Critical whisker length for buckling versus whisker diameter

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Fig. 14

Puncture strength versus hours in a T/H chamber

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Fig. 15

Schematic of tin whisker nucleating on tin coated substrate




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