Thermoset Plastics for MID

TABLE 2.4 Important Properties of Thermoplastics Suitable for Laser Direct Structuring [7, 22, 147] 

The differences in thermai expansion between copper and LDS plastic, particularly the partially crystalline types such as PET/PBT, PA 6/6T, and PPA, some of which exhibit abrupt changes at the giass transition, have long-term negative effects on the adhesive strength of the metaiiization and therefore on the serviceability of the MID. TCP is a materiai weii suited for MID applications for which only a slight mismatch between the coefficients of thermal expansion (GTE) of the plastic and the conductors is admissibie. 

However, the reiativeiy high price of TCP remains a motivator for the development and production of new high-performance materials so that MID suitable for lead-free soldering can still be produced economically. The thermoset, moldable compounds that are not yet the accepted state of the art in MID technology have properties profiles that appear to offer more than enough points of departure for use as substrate materials for molded Interconnect devices. 

Thermoset moldable compounds can be mixed with a very wide variety of fillers to modify their properties to meet the requirements for a given application. Adding suitable fillers can produce coefficients of thermal expansion and elongation behavior virtually identical to those of copper. Once thermoset materials have cured, moreover, their three-dimensional molecular network structure gives them a very high level of dimensional stability. Consequently, in terms of temperature resistance to soldering many of the materials in this class are potentially suitable as MID substrates. Table 2.5 summarizes some of the important thermal properties of commercially available thermoset moldable compounds. Thermoset moldable compounds, moreover, have economic potential because in some cases the cost of the material Is low. Phenolic resin moldable compounds in particular are available at a price of less than about 7 (EUR 5) per kg and could therefore be considered an economical alternative to LDS high-temperature thermoplastics. 

TABLE 2.5 Important Thermal Properties of Selected Thermoset Moldable Compounds [136,167] 

---