Long-term thermal aging of parylene conformal coating under high humidity and its effects on tin whisker mitigation

Journal Article · Tue Jul 06 00:00:00 EDT 2021 · Polymer Degradation and Stability

DOI:https://doi.org/10.1016/j.polymdegradstab.2021.109667· OSTI ID:1838611

Sivakumar, Preeth ^[1]; Du, Surbhi Mahajan ^[2]; Selter, Matt ^[2]; Ballard, Imani ^[2]; Daye, John ^[2]; Cho, Junghyun ^[1]

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1. State Univ. of New York (SUNY), Binghamton, NY (United States)
2. Kansas City National Security Campus (KCNSC), Kansas City, MO (United States)

Usage of pure tin (Sn) or Sn-rich alloy in electronics industry is growing, which makes them more susceptible to the spontaneous growth of tin whiskers. The risk of having these whiskers can be dramatically mitigated by applying a conformal coating provided that it not only possesses excellent mechanical and adhesion properties but also maintains these properties throughout their service. Parylene C is commonly used as a conformal coating because of its favorable mechanical and physical properties, as well as superior conformal coverage. The purpose of this paper is to investigate the degradation of parylene C coating during the thermal aging in high humidity environment (85°C/85% relative humidity for up to 5000hrs) and its effect on the tin whisker mitigation capacity. It was observed that during aging at high temperature and high humidity (HTHH) environment, the oxidation occurs at early times, followed by bond scission, resulting in the loss of strength of the coating. Thinner parylene coating (12.5-μm-thick) had better coating adhesion on the silane-treated tin surface, so provided the better protection for tin whisker penetration than the thicker counterpart (25-μm-thick). After 2500hrs of aging, due to the degradation of the silane agent at the tin/parylene interface, the adhesion of the parylene coating was significantly weakened on the tin surface, which resulted in extensive corrosion of the tin solderpads. The loss of adhesion of the coating, along with the corrosion of the tin surface facilitated the tin whisker nucleation at the interface while the loss of mechanical strength and the brittleness made the coating easily penetrated by the growing whiskers. Tin whiskers with a smaller diameter were buckled and grew along the delaminated region while those with a larger diameter penetrated and continued to grow through the coating. Hence, the effectiveness of the parylene coatings on tin whisker mitigation is significantly reduced under long exposure to such high temperature and high humidity.

• Research Organization: Kansas City Nuclear Security Campus (KCNSC), Kansas City, MO (United States)
• Sponsoring Organization: USDOE; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: NA0002839
• OSTI ID: 1838611
• Alternate ID(s): OSTI ID: 1809889
• Report Number(s): NSC--614-3392
• Journal Information: Polymer Degradation and Stability, Journal Name: Polymer Degradation and Stability Vol. 191; ISSN 0141-3910
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Adhesion
Coating degradation
Long-term HTHH
Parylene
Tin whisker mitigation