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A new pure tin process is described which produces a deposit with a crystal orientation combination that minimises whisker growth, particularly when used with a specific…
A new pure tin process is described which produces a deposit with a crystal orientation combination that minimises whisker growth, particularly when used with a specific pre‐treatment process. A recommended etch depth of minimum 2.5 μm has been shown to reduce whisker growth, particularly with thin (3 μm) tin coatings. Crystal orientation is determined by X‐ray diffraction and the angles between adjacent crystal planes are calculated from the pattern produced. A minimum proportion of small angles is required for lowest whisker risk. Angles smaller than 22° have been shown to be critical. The predominant orientations of the deposits from new tin process are 101, 211, 112, and 312. This combination of orientations has 8 percent of angles in the critical range. A typical pure tin process with a high tendency for whiskering may have a texture of 431, 321, and 211 orientations, and this combination produces 65 percent of angles smaller than 22°.
To present a new tin plating process which provides deposits having a fine‐grained structure and stable crystal orientation with a combination of properties which are well…
To present a new tin plating process which provides deposits having a fine‐grained structure and stable crystal orientation with a combination of properties which are well suited for use as a lead‐free finish on semiconductor lead‐frames.
The new process was designed to produce tin coatings with a deposit grain size ca 20 per cent that of a traditional matte pure tin finish to ensure that the deposit retains good solderability after steam ageing.
The enhanced solderability from the finer‐grained deposit has been demonstrated and other functionally important deposit properties have been confirmed. A stable single crystal orientation 〈220〉 indicates low whiskering propensity and measurements have confirmed the excellent whisker performance, even without specific whisker‐preventing countermeasures. The deposit has high ductility. Analytical methods are available for all key components to ensure optimum process control. The process has been tested in a continuous production environment for over 12 months with excellent results.
The novel process described in the paper provides tin deposits having a unique combination of properties and with production‐proven capability to be an ideal lead‐free solution as a solderable finish for electronic components.
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