EMC across the board

Robert John Webber advocates design rule adoption for beating EMC problems

Jonathan Newell visits Harwin to discuss the increasing importance of factoring EMC into PCB design at an early stage.

From its recently expanded factory in the north Portsmouth suburb of Farlington, Harwin has been supplying its own designed and built cables and PCB hardware since well before the advent of the modern computing era.

Since the early days of the company’s formation, the industry has hurtled along a path of inexorable miniaturisation accompanied by increasing densities and higher demands on connectivity and robust reliability.

Staying agile in such an environment is vital for remaining competitive and Harwin has the agility and foresight to make changes to its products and manufacturing facilities to stay ahead of the next wave of change in the electronics sector.

To find out more about the latest products and the company’s approach to EMC, I visited the Portsmouth factory and spoke to EMC Product Strategy Manager, Robert John Webber.

Navigating EMC complexity

Electro Magnetic Compatibility (EMC) has never been the easiest branch of electrical engineering and is becoming more complicated as circuitry becomes more densely populated, frequencies become higher along wires and antennas proliferate. I asked Webber whether it was governed by very precise rules or whether it was something of a black art.

“It certainly isn’t a black art but it’s very complex. The laws of physics make it very predictable of course but there are a lot of parameters to consider and there is an art to this,” he explained.

He went on to explain that good design from the start is essential and although there is no substitute for thorough testing, careful thought and experimentation at the design stage can prevent many problems.

“If you think of the board layout from the very start and how it will affect EMC performance, then the design will be less iterative,” says Webber.

Going through a process of re-designing and making corrective changes is bad for a number of reasons, not least of which is that each iteration has a potential effect on the product’s EMC performance.

Webber explained that there are a set of design rules that are well established for improving the outcome of board designs. “These design rules are based on standards, experience and experiments. They’re not set in stone and could change as densities increase and will certainly become more critical,” he told me.

An environment in flux

Changes in densities and the resulting overcrowded EMC environment are certainly creating a challenge to design engineers and prototyping is becoming more important for producing a compliant product.

Shielding is essential in reducing emissions from noisy components or protecting these components from a noisy environment. Cans, which cover critical or sensitive components, are an extension of the PCB ground plane, which provides a large surface area to prevent the board from becoming an antenna for emitting or receiving RF. These shielding cans are able to be surface mounted or can be attached using the older through hole and wave solder method.

However, as Webber explained, both of these techniques are expensive in terms of the amount of solder used and the effort required in reworking and inspecting.

To overcome this and to facilitate easier prototyping, Harwin supplies its EZ-BoardWare Shield Cans as well as its prototyping kits. Using the kits, engineers are able to form their own size and shape of shielding can and rework it to achieve optimum performance before placing an order for production volumes.

Using the Harwin can / spring clip approach to attachment also makes it easier to assemble without the use of solder paste or wave soldering processes.

Clip together assemblies

The way Harwin achieves its easy assembly board hardware approach is through the use of spring clips. The clips attach to the ground plane of the board to ensure continuous, solid grounding, including the components attached to the clips.

The universal spring clips are first attached to the board using surface mount pick-and-place equipment and solder paste. The EMC can is then hand pushed onto the clip ensuring ground continuity across the shielding can.

There are a range of clips available, which can be supplied with different retention forces for hand removal or for solder removal. Sometimes, the hand force removal option is good for final products where service access is regularly required to the component beneath the shielding can. The example used by Webber was on smart meters.

The clips themselves are of a stamped and plated construction and so they’re very inexpensive. They can also be used on signal contacts from antennas to boards.

The clips come in a wide range of designs, sizes, compression forces, heights and spring displacements to suit size restrictions and proximity factors from one component to another.

Webber told me, “Our main focus is to meet the requirements of new markets in connected industry through innovative design and so we prioritise product development.

The company produces test reports for all of its products to give its clients confidence in what they’re purchasing and this doesn’t just extend to EMC, but also to vibration response. Vibration can be a significant factor in the reliability of spring contacts.

Cabling

Harwin is well known as a connectivity specialist, supplying a wide range of electronic connectors and Webber explained to me that EMC is becoming more significant in cable connection design now. “Signal frequencies are becoming much higher down the cable now and at very high frequencies, the wires turn into antennas,” he told me.

The cables themselves have better shielding options than ever before but often the connectors are lagging behind. At Harwin, a lot of design effort is put into the connector design so that the back shell of the connector extends the cable shielding to the connector so that there are no exposed wires that could present an EMC risk. “Well designed back shells provide good protection from absorption,” he said.

Compliance from the start

Harwin has invested heavily in the development of products that provide engineers with flexible design options for overcoming the challenges of EMC in crowded RF environments. By employing such products as the prototyping shielding can kit in the early stages of PCB design, product development costs can be reduced as well as the time spent on re-designing and re-working using “permanent” solder technologies.

As component densities further reduce and the RF environment becomes even more crowded, such tools will gain even more significance in the future.

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