## 5 Plasma Precursors
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Scores** & **Score Explanation** \\ \hline  & & Gases that readily form highly reactive species (e.g., \\  & High Scores & O* and H*) leading to efficient chemical breakdown of \\  & (8–10) & common organic residues (oils, polymers, and photo \\  & (8–10) & resistant residues) into volatile byproducts, with \\ Removal of Organic & & numerous studies demonstrating high cleaning rates. \\ Contaminants through Chemical & Moderate Scores & Gases that show some effectiveness, but may be \\ Reduction and Oxidation & (4–7) & slower, less versatile for a broad range of organics, or \\  & (4–7) & require more aggressive plasma conditions. \\ \cline{2-3}  & Low Scores & Gases that are largely inert toward organic \\  & (0–3) & contaminants via chemical pathways or primarily rely \\  & & on physical removal. \\ \hline  & & Gases (primarily H\({}_{2}\) or H\({}_{2}\)-containing mixtures) \\  & & whose plasma species (e.g., H*) efficiently reduce \\  & High Scores & common metal oxides (e.g., copper oxides and tin \\  & (8–10) & oxides) on lead frames to the base metal, with \\  & & evidence of successful surface cleaning and \\ Removal of Oxides Through & & restoration of solderability/bondability. \\ Chemical Reduction & Moderate Scores & Gases showing limited or slower oxide reduction \\  & (4–7) & capabilities or effectiveness only under specific \\  & (4–7) & conditions (e.g., elevated substrate temperatures). \\ \cline{2-3}  & Low Scores & Gases that do not chemically reduce metal oxides or, \\  & (0–3) & in fact, promote oxidation (e.g., O\({}_{2}\)). \\ \hline  & & Inert gases whose ions (e.g., Ar+ and Xe+) have \\  & High Scores & appropriate mass and can be accelerated to energies \\  & (8–10) & effective for sputtering thin contaminant layers, light \\  & & oxides, or for surface roughening/activation, without \\  & & significant chemical alteration. \\ \cline{2-3} Physical Bombardment Efficacy & Moderate Scores & Gases with some physical cleaning capability, but are \\  & (4–7) & less efficient due to lower ion mass, lower ionization \\  & & efficiency, or competing chemical effects. \\ \cline{2-3}  & Low Scores & Gases whose ions are too light for effective \\  & (0–3) & bombardment cleaning activity or where chemical \\  & & reactivity overwhelmingly dominates any \\  & & physical effect. \\ \hline  & & Gases and associated plasma conditions reported to \\  & & cause minimal physical or chemical damage to \\  & & sensitive semiconductor dies or delicate lead frame \\  & (8–10) & features (e.g., thin plating and bond pads). This \\  & & includes low sputtering of substrate, no detrimental \\  & & chemical etching, and minimal risk of issues like \\  & & hydrogen embrittlement when properly controlled. \\ \hline  & & Gases that are generally safe but may pose some risk \\  & (4–7) & under non-optimized conditions (e.g., potential for \\  & & slight oxidation, minor etching, or requiring careful \\  & & control of ion energy/flux). \\ \hline  & & Gases known to be aggressive toward common \\  & Low Scores & semiconductor/lead frame materials (e.g., strong \\  & (0–3) & etchants like fluorine, highly oxidizing like pure O\({}_{2}\) \\  & & for certain metals if uncontrolled), posing a significant \\  & & risk of damage. \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Parametric scoring criteria used for the comparison of the plasma precursors.