Relevant Thermal Characteristic Values for MID

Of the many thermal characteristic values measurable for polymers, two that are highly relevant for molded interconnect devices are glass transition temperature (for amorphous and partially crystalhne thermoplastics) and melting temperature Tu (for partially crystalline thermoplastics). They can be determined by dynamic mechanical analysis (DMA) or differential scanning calorimetry (DSC). Other characteristic properties of primary importance are (short-term and long-term) service temperature and heat deflection temperature, as are temperature response and heat conductivity and the thermal expansion of the thermoplastic substrate materials. 

The substance and significance of the thermal expansion of plastics is discussed in more detail below. The reason is that MID are multimaterial systems, consisting of polymer substrate (thermoplastic, and in the future thermoset plastics as well), metal (e.g., Cu-Ni-Au), and electronic devices. Fig. 2.7 illustrates this, taking an MID conductor structured by laser direct structuring by way of example. 

FIGURE 2.7 Microscope image of a laser direct structured, wet-chemically metallized Cu/Ni/Au conductor on a PET/PBT blend 

The expansion of plastics in response to temperature is much more pronounced than that of metals. The thermal expansion of the plastic is superimposed with reversible and irreversible effects that lead to a change in the linear transient with temperature. 

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