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Smart Cover Len's Design for Smart HMI.

Richard Applin

By Richard Applin.


Halo Logo
Cover Lens Design

For HMI Designers the Cover Lens forms the outer surface of the product, and the first point of interaction for the user.

Custom Cover Lenses fulfill the unique aesthetic and material requirements of any industrial application. 

Incorporating impact resistance requirements, toughness and scratch resistance, as well as moisture and dust ingress protection, the Cover Lens and method of bonding are critical to successful HMI Design.

How Does Halo Deliver Seemless HMI Cover Lens Integration?

Whether a product is Touch or Non Touch based, the Cover Lens is integral to the design. Halo places significant emphasis on consultative design with our client's , defining form, fit and function, material properties and special features. Here are some of the main design considerations:

IK Rating. IK ratings help to classify products by their

resistance to impacts, which is especially useful when

considering hand held devices, which can be dropped from

height. Halo utilises Chemically Strengthened Glass to ensure

even our standard lens materials meet IK06 ratings. For very

rugged applications, we can use IK09, thicker substrates,

and even tailor the PCT Sensor IC to enable Touch

Activation at thicknesses of 6mm or greater.

                                                                                                                                   Optical BondingHalo deploys Optical Bonding in almost all client

                                                                                                            projects. Filling the air gap with an Optical Clear Adhesive or Film

                                                                                                            /Resin, depending on the size and weight of the combined layers, 

                                                                                                            provides moisture and dust ingress protection, higher contrast ratio,

                                                                                                            and impact resistance.

                                                                                                            The Optical Bond is made between the Cover Lens and the Display

                                                                                                            and is usually 0.1mm or thereabouts in thickness. The process is not

                                                                                                            considered re-workable, and careful attention must be paid to curing

                                                                                                            to ensure that small bubbles do not evolve over time, when subject

                                                                                                            to changes in pressure during transportation or operation.

                                                                                                            Once the preserve of higher value niche product design, in Military

                                                                                                            and Medical applications, Optical Bonding is now widespread.


Curved Lens design is increasingly relevant with the advent

of Smart Controls for Industrial and Home Automation design.

Combined with rounding or corners of beveled edges, Design

Engineer's are increasingly experimenting with unique shapes,

form factors and sizes.

Often the Design Engineer will specify an oversized border

lens design with large rounded edges for form an oval or

significantly rounded front design, combing hidden till lit

black Silk Screen Printing with smoked effects delivering

varying levels of opacity. 

                                                                                                            ESD Design Engineers will be required to meet certification for EMC

                                                                                                           and ESD related to their specific sector. For instance, 15 KV ESD for

                                                                                                           Air Discharge and 8 KV ESD for Contact Discharge is common in

                                                                                                           ISO13486 Medical product design certification.   

                                                                                                           Halo often advises clients to add some overlap in the boredr of the

                                                                                                           Cover Lens, to ensure that the charge path is located further from the

                                                                                                           risk components and display IC.                                                
































Cracked TFT
Smart Control Curves Cover Lens
ESD Path

The diagram on the left clearly shows an identified discharge path, where ESD is able to contact the TFT FPC. Analysing various materials to fill the gap with, the table below demonstrates the required thicknesses to mitigate an 8KV discharge event. The best performing material for thickness would be an ESD Acrylic Tape.

ESD CHarge DIstances

The tape can be implemented to fill the gap . 3M provide suitable gasket DST (Double Sided Tape) , which can be deployed to adhere the display within a  recess, but also tackle 8 KV discharge events. Halo often consults clients to design a Double SIded Adhesive Gasket for their lens.

Speak to us today to understand more about designing smart and novel Cover Lenses to enhance your HMI Design.

Screen of a smart digital thermostat with the external and target temperatures indicated.

Holes and Cut Through Features. As a Design Engineer you may be challenged to deliver tactile controls which need to protrude through the border of the Display Cover Lens.

This could be in the form of a Rotary Switch, or a physical button. Either way Halo is able to use laser cutting techniques to machine holes straight through the lens material delivering a unique integrated tactile HMI Design.

Consideration is given to mechanical integrity, as holes created too close to the edge of the Cover Lens could lead to weakening mechanically. Holes are also recommended to integrate rounded internal edges to aid stability.

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