Using 3D-Printed Parts Around Sensitive Electronics: ESD Is More Than a Material Choice

When a 3D-printed part is going to be used around electronics, choosing an ESD-capable material is only one part of the specification. The finished component still has to suit the way it will be handled, what it will come into contact with and the ESD controls already in place.

A board carrier is a useful example. Mechanically, the requirements are fairly easy to recognise. It needs to hold the board properly, locate it consistently and survive normal handling. Electrically, there is more to consider. Charge can be generated as the carrier is handled or as the board is inserted and removed. The carrier may also need to work as part of an existing ESD-controlled area rather than as an isolated component.

An enclosure around an electronic assembly has a different job again. So does a component used close to a PCB during repair or assembly. All three applications could lead somebody to ask for an “ESD-safe” printed material, but that description alone doesn't tell us enough about the part.

ESD control is normally managed as part of a wider programme covering the materials, grounding arrangements, handling conditions and verification methods used around sensitive devices. For a printed component, the useful starting point is what it needs to do electrically once it is in use.

The material data gets you part of the way

There are good industrial materials available for these applications.

ABS-ESD7 provides an electrostatic-dissipative FDM route. Antero 840CN03 provides an ESD-capable route where a higher-performance PEKK-based thermoplastic is required, while LOCTITE 3D IND3380 ESD provides a photopolymer option for applications suited to P3/DLP production.

They are not interchangeable, and the ESD requirement is unlikely to be the only reason for choosing between them.

Size matters. So does temperature, mechanical load, wear, chemical exposure, accuracy, surface requirement and the quantity of parts required. A large board carrier has a different manufacturing problem from a small detailed component that sits around connectors on a PCB.

There is also a tendency to look at a resistance value on a material data sheet and carry that number straight across to the finished component. With additive manufacturing, I would be careful about doing that.

We have some useful data within D2M from evaluating the electrical performance of ABS-ESD7 parts produced by FDM. Across the parts evaluated, the measured resistance remained within the ESD-safe range. The study covered several printer platforms and build orientations, and also assessed tray position, distance from the platen, wall thickness and infill.

Those results are useful, but they apply to the printers, parts and geometries that were evaluated. They are not a reason to assume that every component printed in ABS-ESD7 will give the same result. If electrical behaviour matters to the application, the finished part still needs a defined requirement and an appropriate way to check it.

Specify the finished part

If I were reviewing one of these applications, I wouldn't consider “print in ESD material” to be a complete requirement.

The part drawing or manufacturing specification should make clear what needs to be checked in the finished component. The level of control depends on the application, but the requirement should be something that can be measured and repeated rather than an assumption attached to the material name.

For some parts, that could mean checking resistance between defined points. In another application the relevant check may involve the component after installation because its electrical behaviour depends on how it contacts the rest of the assembly. Appropriate resistance measurement and compliance verification methods should therefore be part of the definition where the electrical behaviour is important.

There is a practical production issue here as well. If a part is accepted and then produced again six months later, somebody needs to know what was actually approved.

For an FDM component that could include the material, machine route, build orientation and any geometry or process conditions that have been shown to matter. If a different printer, material batch, design revision or manufacturing route is introduced later, it should be possible to decide whether the change matters rather than starting from memory.

We already treat dimensions in this way. A 20 mm feature is not controlled because somebody selected a machine capable of producing 20 mm features. The feature is defined on the part and checked against its requirement. An electrical property that matters to the function of the component deserves the same treatment.

The interfaces need some thought as well

The printed material is only one element in the final assembly.

A tray may sit on a grounded workstation. A housing may be attached through metal fasteners. A removable component may rely on contact with another conductive or dissipative surface. Another part may have no intended connection to ground at all.

Where the ESD design relies on a controlled electrical path, the interfaces need to support it. Conductive and dissipative items used inside an ESD-controlled environment may depend on grounding or equipotential bonding, but the correct arrangement depends on the application and the wider control system.

In the finished printed part, that brings fairly ordinary mechanical details into the electrical discussion.

Where does a metal fastener touch the component? Is there a coating at the interface? Will the contact surface wear? Does dirt or repeated handling change the connection over time? Is the part being tested in the condition in which it will actually be used?

None of those questions requires a complicated ESD theory lesson. They are simply part of designing the assembly properly.

A useful electronics example

A recent PCB repair application involving Nokia, Kurtz Ersa and Henkel uses a customised printed component produced in LOCTITE 3D IND3380 ESD as part of a tool used around temperature-sensitive electronics. The design also incorporates a metal element, so the solution is not just a block of ESD resin with the right shape. Geometry, thermal behaviour and ESD performance are being dealt with together in one application.

I think this is a more useful way of looking at additive manufacturing for electronics.

The benefit of printing the component is its ability to suit the board and the process. The ESD-capable material makes that geometry usable in an environment where electrostatic behaviour matters. Other parts of the design deal with requirements that the printed material is not being asked to solve on its own.

That tends to be how real applications develop. There is rarely a single material property that decides everything.

What I would want defined before producing the part

For a new application around static-sensitive electronics, there are a handful of things worth agreeing before moving into repeat production:

• what the component is doing and what it will contact during use;
• the electrical requirement for the finished part and the method used to check it;
• the other mechanical, thermal, chemical and dimensional requirements;
• the material and additive manufacturing process being used;
• any build or geometry variables that need to remain controlled;
• whether the part relies on grounding or another electrical interface once installed;
• what will be recorded as the accepted manufacturing condition;
• which changes would require the part to be checked again.

The amount of work behind those points should match the application. A simple carrier used internally does not need to become a research project. Equally, if a part is being introduced specifically to protect sensitive electronics, there is not much value in specifying an ESD material and never confirming how the actual component behaves.

Where additive manufacturing fits

There are good reasons to use additive manufacturing for this type of work. Electronics production often involves components that are specific to a product, board geometry or process. Quantities may be relatively small, designs can change, and conventional manufacture can be disproportionate for a tray, enclosure or specialised component that only exists to support one configuration.

The flexibility is useful, but it doesn't remove the engineering requirement.

D2M can help with the application review, process and material selection, and the definition of a production route where ESD behaviour needs to be considered alongside the normal mechanical and operating requirements. Our existing ABS-ESD7 work also gives us measured data to work from when an FDM route is being considered, rather than treating the material designation as the end of the discussion.

If a printed tray, enclosure or component is going to be used around sensitive electronics, the aim should be fairly straightforward: specify what the finished part needs to do, choose a manufacturing route that can deliver it, and check the property that matters before putting the component into use.