Joining of Contact Pins and Conductive Compounds via Injection Molding – Influence of the Flow Situation on the Electrical Contact Resistance

Abstract

While a lot of research can be found in the field of bulk resistance of carbon filled polymers, comparatively few papers focus on contact resistance between compound and metal contacts. Due to that small number of researches that deal with contact resistances, studies of the influence of injection molding conditions and parameters on the contact resistance are also very rare. In contradiction to that, these influences on bulk resistance have been studied. The objective of this work was to investigate the electrical contact resistance of overmolded tinplated copper contacts after modifying flow situations and molding conditions by procedural and constructional methods in contact areas. Metal pins were overmolded with a polypropylene compound containing 45 vol.% graphite, utilising an insert injection molding process. To affect the flow situation at the contacts, several processing parameters, such as mold temperature and injection speed, were modified. In addition, the contact alignment related to melt flow direction was varied. Electrical properties were studied and related to macroscopic and microscopic connection properties and flow situations in contact regions. It was found that the contact resistance is a significant factor while examining electrical resistances of overmolded samples. Furthermore, it was shown that the various flow situations had an essential impact on contact resistances. Weld lines at the position of the contact caused a decreased contact resistance. The correlation of the weld line effect, the filler orientation and contact resistance were successfully investigated by μ-CT. Regarding processing parameters, it was observed that a high mold temperature of 120 °C increased not only bulk conductivity, but also had a positive impact on contact conductivity. Macroscopic and microscopic connection mechanisms of contact surfaces were interpreted and connected to the experimental observations.

Determination of Local Electrical Properties Using a Potential Field Measurement for Electrically Conductive Carbon Fiber Reinforced Plastics with Metal Contact Pins Joined via Injection Molding

“…In particular, the local orientations and filler concentrations should be mentioned here [ 14 , 15 ], as well as the potential formation of weld lines, which have an influence on the local fiber distribution [ 16 , 17 ] and thus also on the conductivity in this area. Due to processing dynamics, electrical properties may vary at different positions, which are placed in different flow situations in an injection-molded specimen [ 18 ]. There is also a correlation between the above-mentioned injection molding parameters and the electrical properties [ 19 , 20 , 21 ].…”

“…While the total resistance of such compounds is already well-studied [ 22 , 23 , 24 ], there are only a few approaches known that deal with the relationship of the local conductivity within such parts in connection with the filler orientation either by means of simulative or experimental methods [ 13 , 18 , 19 ]. In addition to determining the electrical properties of anisotropically filled polymer materials, the contact between such materials and metal parts is also a relevant topic.…”

“…In addition to determining the electrical properties of anisotropically filled polymer materials, the contact between such materials and metal parts is also a relevant topic. Approaches for the measurement of the electrical resistance of areas close to the contact as well as for modeling the contact mechanisms are available [ 18 , 25 ]. Direct overmolding of electrical metal contact pins by means of assembly injection molding offers particularly high potential for application scenarios involving the functionalization of injection-molded components.…”