## 4 Plasma Interaction with Surfaces  
With respect to the handling of lead frames, the literature has indicated the existence of two types of plasma cleaning systems, namely batch-type and strip-type. Batch-type plasma systems are used in cleaning processes involving high volumes. This type of plasma cleaning utilizes slotted magazines in which a number of lead frames are placed. The processing time for this type of plasma is typically longer than that used in strip-type plasmas; however, one must of course keep in mind that many lead frames are being processed at the same time. Batch-type plasma processes typically do not produce the same level of uniformity as can be found in strip plasma, since the lead frames are in different positions within the chamber [3]. Strip-type plasma cleaning systems allow the plasma to be applied directly to the lead frames, which are introduced into the chamber sequentially. The maximum ion concentration is able to reach the surface of the lead frame when this configuration is used. Uniformity of action was also confirmed in the reviewed literature. On the negative side, it must be said that strip plasma systems require significantly more handling of strips and also normally clean one lead frame at a time, thus having low throughput [3]. For both the batch-type and the strip-type plasma, gas flows into the chamber can either be pulsed or continuous. Pulsed flow allows for a program to be set up where the gas flow of particular gases can be stopped and started during the ongoing plasma cleaning process. In pulsed flow processes, the various gases are introduced separately and sequentially into the chamber. The literature has indicated that introducing the reactive gases over a short period of time, say over 2 s, avoids increased oxidation and surface etching. For reactive gases, the literature indicated that high flow rates can dislodge physical contaminants from the surface of the lead frame. On the other hand, inert gases are introduced at low flow rates over a longer period of time, say 10 s [3]. Continuous-flow processes are those in which gases, inert and reactive, are introduced into the chamber together at a flow rate that is fixed. The reviewed experimental work indicated that a constant flow over a longer time period demonstrated an improvement in wettability and uniformity over pulsed-flow processes [3]. A key difference of DBD plasmas and DC plasma systems compared with other types is the possibility to operate at atmospheric pressures without the need for a vacuum chamber. However, the literature has indicated that plasma systems operating at near-vacuum pressures are preferred over atmospheric plasmas for semiconductor cleaning applications due to several key advantages, one of which is contamination control [67]. Under such conditions of very low gas pressures, there is a reduced presence of airborne contaminants and particulates that could settle on semiconductor surfaces. This \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **References** & **Parametric Score** \\ \hline Electron Temperature & Limited literature was found in this area; however, the reviewed text indicated that electron temperature for DCSBD plasmas tend to be lower than DBD plasmas, which in turn is significantly less than that found in vacuum plasmas. In DCSBD plasmas, which operate at atmospheric pressure, electrons collide very frequently with gas molecules, losing energy in these collisions, thus keeping their average energy relatively low. DCBSC plasma systems are generally used for gentle large-area processing [65; 66]. & 7/10 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: _Cont._means that vacuum plasmas allow for cleaner reactions with fewer unwanted byproducts. The literature has also indicated that vacuum plasmas offer better plasma uniformity since, in a vacuum, the mean free path of plasma species is longer, leading to more uniform and controlled energy distribution, which is critical for precise semiconductor processing.