The five levels of control
Level 5 is the level of electronic batch records. At this level, the management of manufacturing control is improved by typically
linking it to ERP and LIMS electronically. This link guards against mistakes in manual transcription. Conformance to standard
operating procedures (SOPs) is increased. Better conformance reduces paperwork errors, which, in turn, ensures that correct
manufacturing sequences are followed and reduces manufacturing mistakes. Paperwork is also reduced at this level, and nonconformances
resulting from paperwork are significantly reduced. Process capability, however, typically does not improve, and process sigma
improves only slightly. This level is a good stage at which to introduce technology to the shop floor, gain experience within
operations, and reconcile and improve data.
MES characterizes Level 4. This level provides automated machine instructions that establish the process parameters in which
the equipment operates. MES typically links ERP directly to the shop floor. This link reduces operator and transcription errors.
Processes are standardized, and operating conditions are measured and recorded. SCADA regulatory requirements are satisfied.
Messages automatically alert operators to out-of-specification operating conditions. Quality and compliance are increased
by additional standardization and mistake-proofing. At this level, process capability may increase slightly if the process
parameters correlated to product attributes are known. Even if this is not the immediate result, the standardization of MES
provides the controlled environment that enables future process improvement.
Level 3 is marked by point-to-point process control. This level of automated process control allows users to modify product
attributes by adjusting process parameters. For example, the amount of active/in.2 in a layer (patch) to be applied to a substrate may be controlled by adjusting the line speed of the coating operation.
The thickness of the layer is measured after coating, and the line speed may be increased or decreased to achieve the targeted
thickness. This control is an example of PAT that FDA has been encouraging during the past several years. At this level, process
capability is increased for the selected operation raising it to more than 1.0 sigma. This measurement means that, most of
the time, the product will be made within specification but will vary within the specifications. Quality and compliance increase,
thus providing significant business results such as improved yields, reduced waste, increased capacity, and fewer errors.
Level 2 is APC. APC is the application of process control to the entire manufacturing process. The manufacturing process can
be within one plant or shared among multiple plants. The process can include suppliers and contract manufacturers. APC allows
operators to adjust a process based upon known data from previous operations, the condition of raw materials to be used in
the process, or the known condition of the equipment tool. As in Level 3, where the thickness of the active coating on a patch
is controlled by line speed, APC achieves the exact concentration of active using data about the concentration of the active
in the coating batch. APC thus attains the correct thickness level based on batch concentration. APC automatically adjusts
from batch to batch.
In addition, the uniformity of thickness across the patch surface is important, and the uniformity of the coating is based
on the batch's viscosity, surface tension, and temperature. APC automatically adjusts machine parameters such as coating-bar
vacuum, web tension, and width between coating rollers to obtain the precise uniform coating based on the batch characteristics.
A key requirement of Level 4 is the integration of data for APC. This integration should be planned ahead of time through
network design. The data elements that are related through various algorithms include metrology data (which are related to
products attributes such as thickness, active concentration, and color), machine parameters (e.g., current, vacuum, and motor
temperature), process parameters generated by machine parameters (e.g., solution temperature, pressure, line speed, machining
speeds, and feeds), logistics data (which identify the material batch and location), event data (such as material consumed
and steps completed within an equipment unit), and other local data from the tool bus such as sensor data.
APC uses various algorithms to determine the relationship between the product attributes and the machine and process variables.
Based on these relationships, APC controls multiple process steps to achieve the desired product attributes. APC operates
in feed-forward and feedback modes as required. Analysis is performed from unit-operations and multivariate perspectives.
Because of its multivariate capability, applying APC improves the process performance to more than 2.0 CpK.