Radiation-Crosslinked Film for Flexible Circuit Carriers
Plastic film must satisfy stringent requirements if it is supposed to function as the substrate for metal circuit traces. These include, among others, the ability to withstand soldering temperatures of over 250°C as well as high mechanical loads during hot stamping. In this regard, film materials produced from engineering thermoplastics approach their limitations. However, new research from the University of Erlangen-Nuremberg show that PA and PBT films can be modified by means of radiation-induced crosslinking in a way that makes them suitable for manufacturing flexible circuit carriers.
Irradiating the film increases its heat deflection temperature. This, in turn, allows the temperature of the hot stamping die to be increased, which ensures better adhesion of the copper circuit traces to the plastic film substrate. In addition, the crosslinked film exhibits greater stiffness, which reduces bulging in the course of hot stamping. The crosslinked film withstands peak soldering temperatures of up to 260° C and can be employed in the conventional SMT process sequence, according to the research team in Erlangen.
Whether the films are suitable for backmolded circuit carriers (3-D MID) was also investigated. In this case, the film is first thermoformed. After radiation-induced crosslinking, the film can be heated beyond the crystallite melting point, since the material behaves elastically in areas where crosslinking has occurred. This makes the films very suitable for thermoforming. Very good adhesion can then be achieved during the subsequent injection molding process.
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