Characteristics of Tin Whisker Growth on Matte Tin Surface Finishes by Acceleration Conditions

Whiskers are pure tin mono-crystal. Electro-deposited tin layer as lead free finish in electrical devices tend to form whiskers. It can be formed soon after plating, several years after plating or even seldom happen. It is one potential danger for device reliability in industry usage. In this paper, whiskers growth on copper and Fe-Ni Alloy42 materials are individually inspected. For Fe-Ni Alloy42 material, thickness effect dominates the whisker growth. For Cu material samples, grain size effect shows major function in the whisker growth. And result show that the plating current density is supposed to be effective in controlling the plating layer grain size. For Cu material, trim/form process may affect the IMC layer growth morphology, which is supposed to be effective to whisker growth. Cross section and top view etch methods are used. The IMC layer morphology is check by SEM. It shows that long period of storage in TCT make the IMC layer flatter. And tins flatness in IMC may explain the cease of whisker growth after long period of time. Cracks are found in the IMC layer for Cu material after long period of TCT condition. Tins may be due to the compressive force generated from the IMC itself.