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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. 4. Formability
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.
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