Conductively filled Poly(methyl methacrylate) composites; manufacture and testing processes for EMI shielding effectiveness

Smuga, Jonathan R.

Abstract

Electromagnetic interference (EMI) is an escalating concern in the modern electronic climate. As such it has become a critical area to consider when designing and packaging electronics. With the growing volume of electronic devices available and with processor frequencies increasing, the electromagnetic environment is becoming ever more congested. The need for adequate EMI shielding has become an essential consideration.
The desire for high performance combined with reductions in size, weight and manufacturing cost suggests that polymers should be ideal materials for parts such as electronic housings. Unfortunately polymers generally do not provide shielding from electromagnetic waves.
The research detailed in this thesis investigates the manufacture and testing of conductively filled poly(methyl methacrylate) (PMMA) composites. Samples of PMMA resin and various electrically conductive filler materials were manufactured. The processing methods, electrical properties and electromagnetic behaviour were all investigated. Composite polymer coatings were printed with a K-Control Coater and evaluated for surface resistivity and EMI shielding effectiveness. Samples were produced with a range of filler materials including nickel, carbon, copper/aluminium and silver coated glass spheres. Shielding effectiveness values of approximately 70 dB were obtained for coatings of PMMA filled with silver coated hollow glass microspheres.
Attempts were made to produce an alternaalternative filler material by electroless nickel plating of expanded graphite powder. Successful plating was achieved using conventional methods of surface sensitisation of the graphite. This however resulted in agglomerations of the powder and a loss of the desired physical properties. Alternative thermal surface treatments proved to be unsuccessful in activating the graphite surface with no nickel deposition occurring.
Furthermore, electroless nickel plating techniques were successfully utilised in the development of an alternative manufacturing process for producing electrically conductive PMMA composites which contained a reduced metallic content, in relation to a more traditional production technique. Plaques were manufactured by compression moulding of nickel plated PMMA granules. These were compared against samples manufactured with nickel powder mixed in a Brabender Plasti-Corder. The electroless plating method produced samples that outperformed the comparative method and were shown to contain a reduced metallic content. Shielding effectiveness of the electroless plated granule samples achieved approximately 34 dB compared to a maximum of only 2.5 dB for the Brabender compounded samples.
Outwith these areas of empirical testing a computer model was produced to simulate the electromagnetic shielding behaviour of composite materials using Comsol Multiphysics. This model appears to successfully simulate the waveguide testing apparatus. However the theoretical conductivity values as calculated from effective media theory resulted in disproportionate shielding effectiveness values obtained.
Further research into the electroless plated and compression moulded PMMA composites would be beneficial in order to fully optimise the process. Equally the theoretical model would require further investigating and validating before more accurate simulations could be achieved.

Thesis Type	Thesis
Deposit Date	Jun 15, 2012
Peer Reviewed	Not Peer Reviewed
Keywords	Electromagnetic interference (EMI); shielding; conductively filled poly(methyl methacrylate) (PMMA) composites;
Public URL	http://researchrepository.napier.ac.uk/id/eprint/5426
Award Date	Jun 15, 2012

Conductively filled Poly(methyl methacrylate) composites; manufacture and testing processes for EMI shielding effectiveness

Smuga, Jonathan R.

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