Why You Should Single-Source EMI Shielding Materials

EMI shielding of electronics using thermoplastic housings traditionally has been a complex and costly process. Today, OEMs not only have to meet form, fit and function requirements, but also must reduce the total cost of ownership, reduce weight, simplify the supply chain and reduce time-to-market.

For these reasons, OEMs will benefit from using a full-service, single-source supplier who can simplify these challenging responsibilities by taking on these tasks and more such as:

• Provide technical expertise in the dispensing, curing and spraying of sophisticated materials
• Reduce complex material requirements of tens of parts down to a single stock keeping unit
• Reduce the size of inventory and eliminate a layer of inventory management processes
• Support customers' quality processes such as the automotive industry's PPAP (Production Part Approval Process) scheme and aerospace and defense certifications

Incorporating expert materials

Parker Chomerics offers an integrated assembly service which pre-assembles and dispenses its products into a housing, heat sink assembly or substrate and delivers a custom product or sub-system according to the customer’s design specification. The sub-system incorporates expert materials such as engineered plastics, thermal interface materials, electrically conductive elastomers and coatings, some of which require expert processing to guarantee quality and functionality. 

Making choices

Selecting a suitable plastic injection molding partner is not as straightforward as it sounds when it comes to electronic enclosures. This is where design assistance from a reputable expert in EMI shielding will be invaluable. Because the optimization of part geometry will lead you to the highest performance with the lowest possible processing, material and tooling cost.  

Additionally, upon part design completion, mold flow analysis will help create a 3D representation of flow patterns for the injection molding process. As a result, it is possible to visualize flow rates, pressures and temperature values across the entire part, therefore helping adjust the molding process by locating entry gates and compensating for variable pressures or cooling rates to avoid part warpage or uneven shrink rates. A specialist in this area will also be able to source the tooling, build the optimum mold and provide full PPAP reporting back to the customer.

With over 300 different polymer materials available for design engineers to consider, expert advice can prove invaluable.  

A superior choice for plastic housings is Parker Chomerics PREMIER™ PBT -- available in two offerings, one that delivers excellent hydrolysis resistance, the other superior 5VA flame retardant, PREMIER PBT improves long term aging performance when exposed to extreme heat and humidity.  It is a superior choice due to its high shielding effectiveness and enhanced mechanical strength.  Also, being a single pellet composition, it eliminates inconsistent mix ratio problems common with multi pellet blends.

Non-conductive thermoplastics can also be used with secondary EMI coatings.  These are most suitable for parts requiring high temperature resistance, chemical resistance, low water absorption, thin walls or those requiring shielding effectiveness > 85 dB.

Parker Chomerics can help with additional processes such as conductive painting, sputtered vacuum metallization, electroless plating and thermal spraying.

The primary design factors to consider when choosing a secondary EMI coating are

• Shielding effectiveness
• Environmental resistance
• Component geometry
• Production volume

For example, sputtered aluminium is a good solution in low-shielding applications where volume supports a higher tooling cost. Alternatively, while Ni/Cu provides excellent shielding, this coating is not generally recommended for use in high-humidity uncontrolled environments, while thermal spraying of tin-zinc provides high shielding with excellent resistance to harsh environments.

Often plastic housing needs assembly of a secondary component.  These elements can be assembled onto the housing using processes such as heat staking, sonic welding, solvent bonding and mechanical assembly. Depending on the part, assembly can often be done at the injection molding press, within the cycle time, consequently saving money for the customer.

Often the device will need EMI shielding, thermal management components or an optical display filter, in line with the customer requirements.  Depending on the application, materials may include extruded, molded or form-in-place EMI gaskets, thermally conductive pads or gels, microwave absorbers or optical displays. These materials can be dispensed, over-molded, bonded, mechanically fastened or incorporated into the design to become an integral part of the housing. This simplifies final assembly, allowing OEMs to have only one part to order, inventory and handle.

Another benefit of integrating all these components using a single-source supplier is that testing of the EMI package and board level design can be done at the beginning of the design cycle therefore eliminating the need for rework and changes further down the line. Specialists can offer full service compliance testing to meet emissions, immunity, susceptibility and safety requirements and is able to solve virtually any EMC/EMI problem that testing may reveal.

Ultimately, through the selection of a single-source supplier who can provide integration of all design and production capabilities globally, it is possible to reduce cost, reduce weight (in metal-to-plastic conversions), reduce time to market and produce a fully integrated assembly that best suits the customers global footprint. Chomerics' Integrated service allows customers anywhere in the world to design a sub-assembly including EMI shielding solutions and TIMs, and then partner with Chomerics to assemble it.

This blog post was contributed by Mel French, marketing communications manager, Chomerics Division Europe.

Related content:

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Metal-to-Plastic Conversion Benefits for Automotive Engineers

Top Three Design Tips for Corrosion Resistant EMI Protection