Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish

Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formatio...

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Autores principales:	Nor Akmal Fadil, Siti Zahira Yusof, Tuty Asma Abu Bakar, Habibah Ghazali, Muhamad Azizi Mat Yajid, Saliza Azlina Osman, Ali Ourdjini
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	immersion tin coating tin whiskers micro-hardness indentation copper substrate JEDEC Standard JESD22-A121A nickel underlayer Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85
Acceso en línea:	https://doaj.org/article/043c4a8c2af548dba0a9ff33ca87ea1b
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spelling	oai:doaj.org-article:043c4a8c2af548dba0a9ff33ca87ea1b2021-11-25T18:13:50ZTin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish10.3390/ma142268171996-1944https://doaj.org/article/043c4a8c2af548dba0a9ff33ca87ea1b2021-11-01T00:00:00Zhttps://www.mdpi.com/1996-1944/14/22/6817https://doaj.org/toc/1996-1944Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formation, which tends to endanger the efficiency of electronic circuits, and even worse, may cause short circuits to the electronic components. This research aims to investigate the effects of stress on tin whiskers’ formation and growth and the mitigation method for the immersion of the tin surface’s finish deposited on a copper substrate. The coated surface was subjected to external stress by micro-hardness indenters with a 2N load in order to simulate external stress applied to the coating layer, prior to storage in the humidity chamber with environmental conditions of 30 °C/60% RH up to 52 weeks. A nickel underlayer was deposited between the tin surface finish and copper substrate to mitigate the formation and growth of tin whiskers. FESEM was used to observe the whiskers and EDX was used for measuring the chemical composition of the surface finish, tin whiskers, and oxides formed after a certain period of storage. An image analyzer was used to measure the whiskers’ length using the JEDEC Standard (JESD22-A121A). The results showed that the tin whiskers increased directly proportional to the storage time, and they formed and grew longer on the thicker tin coating (2.3 μm) than the thin coating (1.5 μm). This is due to greater internal stress being generated by the thicker intermetallic compounds identified as the Cu<sub>5</sub>Sn<sub>6</sub> phase, formed on a thicker tin coating. In addition, the formation and growth of CuO flowers on the 1.5 μm-thick tin coating suppressed the growth of tin whiskers. However, the addition of external stress by an indentation on the tin coating surface showed that the tin whiskers’ growth discontinued after week 4 in the indented area. Instead, the whiskers that formed were greater and longer at a distance farther from the indented area due to Sn atom migration from a high stress concentration to a lower stress concentration. Nonetheless, the length of the whisker for the indented surface was shorter than the non-indented surface because the whiskers’ growth was suppressed by the formation of CuO flowers. On the other hand, a nickel underlayer successfully mitigated the formation of tin whiskers upon the immersion of a tin surface finish.Nor Akmal FadilSiti Zahira YusofTuty Asma Abu BakarHabibah GhazaliMuhamad Azizi Mat YajidSaliza Azlina OsmanAli OurdjiniMDPI AGarticleimmersion tin coatingtin whiskersmicro-hardness indentationcopper substrateJEDEC Standard JESD22-A121Anickel underlayerTechnologyTElectrical engineering. Electronics. Nuclear engineeringTK1-9971Engineering (General). Civil engineering (General)TA1-2040MicroscopyQH201-278.5Descriptive and experimental mechanicsQC120-168.85ENMaterials, Vol 14, Iss 6817, p 6817 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	immersion tin coating tin whiskers micro-hardness indentation copper substrate JEDEC Standard JESD22-A121A nickel underlayer Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85
spellingShingle	immersion tin coating tin whiskers micro-hardness indentation copper substrate JEDEC Standard JESD22-A121A nickel underlayer Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85 Nor Akmal Fadil Siti Zahira Yusof Tuty Asma Abu Bakar Habibah Ghazali Muhamad Azizi Mat Yajid Saliza Azlina Osman Ali Ourdjini Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish
description	Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formation, which tends to endanger the efficiency of electronic circuits, and even worse, may cause short circuits to the electronic components. This research aims to investigate the effects of stress on tin whiskers’ formation and growth and the mitigation method for the immersion of the tin surface’s finish deposited on a copper substrate. The coated surface was subjected to external stress by micro-hardness indenters with a 2N load in order to simulate external stress applied to the coating layer, prior to storage in the humidity chamber with environmental conditions of 30 °C/60% RH up to 52 weeks. A nickel underlayer was deposited between the tin surface finish and copper substrate to mitigate the formation and growth of tin whiskers. FESEM was used to observe the whiskers and EDX was used for measuring the chemical composition of the surface finish, tin whiskers, and oxides formed after a certain period of storage. An image analyzer was used to measure the whiskers’ length using the JEDEC Standard (JESD22-A121A). The results showed that the tin whiskers increased directly proportional to the storage time, and they formed and grew longer on the thicker tin coating (2.3 μm) than the thin coating (1.5 μm). This is due to greater internal stress being generated by the thicker intermetallic compounds identified as the Cu<sub>5</sub>Sn<sub>6</sub> phase, formed on a thicker tin coating. In addition, the formation and growth of CuO flowers on the 1.5 μm-thick tin coating suppressed the growth of tin whiskers. However, the addition of external stress by an indentation on the tin coating surface showed that the tin whiskers’ growth discontinued after week 4 in the indented area. Instead, the whiskers that formed were greater and longer at a distance farther from the indented area due to Sn atom migration from a high stress concentration to a lower stress concentration. Nonetheless, the length of the whisker for the indented surface was shorter than the non-indented surface because the whiskers’ growth was suppressed by the formation of CuO flowers. On the other hand, a nickel underlayer successfully mitigated the formation of tin whiskers upon the immersion of a tin surface finish.
format	article
author	Nor Akmal Fadil Siti Zahira Yusof Tuty Asma Abu Bakar Habibah Ghazali Muhamad Azizi Mat Yajid Saliza Azlina Osman Ali Ourdjini
author_facet	Nor Akmal Fadil Siti Zahira Yusof Tuty Asma Abu Bakar Habibah Ghazali Muhamad Azizi Mat Yajid Saliza Azlina Osman Ali Ourdjini
author_sort	Nor Akmal Fadil
title	Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish
title_short	Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish
title_full	Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish
title_fullStr	Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish
title_full_unstemmed	Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish
title_sort	tin whiskers’ behavior under stress load and the mitigation method for immersion tin surface finish
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/043c4a8c2af548dba0a9ff33ca87ea1b
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Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish

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