Advantages of Hot Dip Tin Coatings vs. Electroplate
1. Metallurgical Bond
a. Hot-Dip: Alloy layer forms between base material and coating which prevents flaking or peeling.
b. Electroplate: Chemical bond is established that frequently results in flaking or peeling, especially near the sheared edge.
2. Dense Structure
a. Hot-Dip: Cast structure, not porous. Few grain boundaries which are paths of diffusion of the base material.
b. Electroplate: Porous structure. The tin grains are piled onto each other to obtain thickness. Many boundaries between grains which are paths for diffusion.
3. Whisker Growth
a. Hot-Dip: Cast structure, large grain size, no inherent stresses. No whisker growth detected.
b. Electroplate: Small grain size, inherent stresses from plating baths. Whiskers readily grow in a pure tin plate. Lead must be added to inhibit whisker growth.
a. Hot-Dip: Cast structure can go through severe deformation with no cracking. (see Figure 2.)
b. Electroplate: Chemical bond, stresses and porous structure. Can crack or peel during severe deformation. Cracks develop at sheared edges. (see Figure 3.)
Figures 1, 2 & 3 are reprinted with the permission of AMP.