## 5 Conceptual Design for Micro Assembly Product Development
### Decision Trees  
The crucial step for the proposed conceptual design approach for micro-assembly is the early link between the product design and the assembly process that is needed for the fabrication of the product. This means that in a very early stage of the product development process feedback on the manufacturability of the product is provided. For this the link between the properties of the product and the subsequent assembly process is needed. In order to standardize this link, decision trees for different phases of the micro-assembly process were developed in Reference [24] that allow a comparatively detailed choice of a specific process step based on the given properties of the product, represented by the above-mentioned data types. When applying the decision tree methodology, the decisions that have to be taken are reduced to a sequence of simple questions that can be easily answered, leading to a suggestion of the appropriate assembly process. \begin{table}
\begin{tabular}{c c} \hline \hline
**Data Field** & **Possible Properties** \\ \hline Identifier & Name of Connection Point \\ Type & Free Surface, Free Volume, Clamping, Jack, Plug, SMD \\ Location & Above, Beneath, Ahead, Behind, Left, Right, In, Through \\ Material Properties & Metallization, Roughness, Optics \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Properties of the Connection Point Data Type. \begin{table}
\begin{tabular}{c c} \hline \hline
**Data Field** & **Possible Properties** \\ \hline Identifier & Name of Component \\ Geometrical Base Form & Box, Cylinder, Tube, Cone, Sphere \\ Weight & Weight in Gramm \\ Temperature Consistency & Minimum Temperature, Maximum Temperature \\ Material Properties & Magnetism, Shock Resistance, Clean Room Class, Optical Property \\ Feeding Possibilities & Tray, Bulk, Tube, Belt \\ Picking Possibilities & Vacuum Gripper, Parallel Gripper, Radial Gripper, Three-Point Gripper, Magnetic Gripper \\ Connection Points & List of Identifiers \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of the component data type. \begin{table}
\begin{tabular}{c c} \hline \hline
**Data Field** & **Possible Properties** \\ \hline Connection Point Partners & Identifier Point 1, Identifier Point 2 \\ Spatial Properties & Position (Above, Beneath, Ahead, Behind, Left, Right, In, Through), \\  & Loose, Offset, Tolerance \\ Physical Requirements & Electric Conductivity, Optics, Stiffness, Stability \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Properties of the relation data type. Exemplarily the decision tree for the joining processes is shown in Figure 5. The decision tree leads to a specific choice between 4 possible joining processes: UV-cured adhesive bonding, adhesive bonding, soldering, and a mere positioning, whereas the choice of the adhesive (whether conductive or non-conductive) can be seen as an additional feature that does not affect the decision on the process and, therefore, needs not to be considered in the decision tree. For each decision tree, different properties of the abstract product representation are used. As shown in the figure, this decision for the joining process is taken based on the following properties:  
* Component properties: Weight, temperature consistency;
* connection point properties: Metallization;
* relation properties: Stability, electric conductivity, tolerance. An analog approach is shown in Reference [24] for the decision on the sequence of the assembly processes. The methodology was established based on the analysis of a cross-section of several different micro-assembly products and validated with four specific products:  
Figure 5: Decision tree for the Joining Processes. Blue are component properties, orange connection point properties, and red relation properties (based on Reference [24]). * Printed circuit board (PCB) based optical module for a rotary encoder;
* surface-mounted device (SMD) assembly of a Flex-PCB;
* molded Interconnected Devices (MID) based light module;
* MID based sensor holder for a hall sensor element.