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Medical equipment and devices must be designed with rigorous standards to function in environments where patient safety and product reliability are critical. Today, there is a great demand for innovative, feature-rich, and affordable electronic equipment to be used in diagnostic labs, hospitals and clinics, as well as for consumer selfcare. Engineers are constantly challenged to deploy differentiating leading-edge electronics that demonstrably improve patient care in a cost-effective manner, for in-home patient care and portable monitoring and therapeutic devices.
In order to build high-performance products that are durable enough to withstand the challenging environments of most medical applications, design engineers need to consider how each component will operate within each medical device. From tiny sensors to sophisticated measurement systems, electronic products contribute to modern healthcare efforts, and they must be designed and manufactured to meet the special set of requirements for medical electronic products. Key attributes for switches used in medical products include high reliability, miniature size, long life cycle, corrosion resistance against body fluids and the option of customisation.
No Contaminants, No Problem. Understanding IP 67
Let’s start with a look at product corrosion resistance against body fluids.
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It is important to note that medical switches are subject to many hazardous events, such as hospital cleaning solutions, human and environmental surface contaminants, water vapour transmission, electrostatic discharge (ESD), and environmental pressure differentials. Since ingress of contaminants represents a key failure mode for switches, Light Touch Switches (LTSW) for medical applications increasingly need to meet IP 67 standards for protection against dust and liquid infiltration.
Today’s wearable devices and hearing aids also nearly always require IP 67 tactile switches to withstand exposure to sun screen, lotion and water. The increased product life provided by an IP 67 rated device typically outweighs the trade-offs in the tactile property of the switch - the silicone makes the switch feel less crisp. If you compare two tactile switches with identical push forces, one with and one without the IP 67 membrane, the switch with the membrane will usually feel a bit spongy.
Yet it’s important to be aware of these trade-offs when selecting tactile switches with a silicone membrane, especially if you’re trying to optimise for switch feel. Panasonic’s IP67 tactile switches are manufactured differently. Rather than bond a silicone membrane under the actuator, Panasonic uses a new patented laser method which welds a thin nylon-based film over the actuator. This new method has a clear edge over traditional membrane construction:
- Preserves crisp switch feel: The laser welded nylon film has only a negligible affect on actuation force abd click ratio.To take one example, the click ratio changed from 70.15% without the laser welded film to 68.28% with it - for a minor two percent change.
- Protects against side loads: Placing the film over the actuator has the side beefit of offering some protection against side loads, which helpsprevent damage to the switch. Traditional membrane construction leaves the actuator exposed to damage from side loads.
Improving Tactile Switch Actuation and Lifecycle
Another contributing factor to the longevity of a medical product is quality, and more specifically, how the end user perceives it. For example, for various laparoscopic procedures, surgeons depend on the tactile feedback from their electro-surgery instruments before cutting and sealing tissue. This is also an extremely important design consideration for insulin pumps, since over time diabetes affects and decreases people’s sense of touch due to progressive nerve damage. Switches are being used in transdermal patches to trigger dispensing of pain killers, antibiotics and other drugs through the skin.
| LTSW by Panasonic for medical applications
Panasonic‘s Light Touch Switches have low contact resistance and provide a unique sharp tactile feel in a very small package. |
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 EVPBBIP-67 (2.6 x 1.6) • Top Push Type • High operability equipped with an actuator |
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 EVPAKIP-67 (3.8x1.9) • Side-operational type • Excellent tactile properties • Measure against mechanical peel-off |
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| EVPAT-type | |
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| Side Push Switches by Panasonic for medical applications | |
 EVPAT(3.4 x 1.7) • Good feel • Measure against mechanical peel-off • Miniature package size |
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EVPAVElderly people who have to operate manual drug meters, such as those involving lower dosage levels of prescription drugs, require a consistent and reliable tactile feedback experience to minimalize misuse and over dosage. It is essential that the switch operates properly, not only to ensure medication is being dispensed, but that the proper dosage is dispensed on schedule. Panasonic’s Tactile Metal Domes are frequently used to provide the “snap” or tactile feedback and audible sound when a switch is user-actuated and have proven a necessary design. The dome array is part of the switch contact system, which is encased in the switch assembly to provide a solid “snap” or tactile response when the switch is actuated.
The design ensures that the moment of tactile response more closely coincides with the moment of contact. The mechanical contact system is extremely reliable in harsh environments and offers a superior tactile response that is consistent from switch to switch. As described in the graph above, all tactile switches have actuation force characteristics that can be expressed as a click ratio that expresses the relationship of the switch’s actuation and contact forces. A higher ratio indicates a “crisper” or “snappier” switch feel. The travel distance, or deflection, of a pressed switch can also contribute to its overall feel. Metal dome or embossed arrays offer easily integrated low-cost contact systems that still allow for custom contact configurations.
The Smaller, the Better – Benefits of Side Push Switches
Size is another key factor in medical device design. Take hearing aids for instance– the hearing technology landscape is ever- evolving and encompasses a wide range of products – from traditional hearing aids regulated as medical devices to consumer-technology products (such as personal sound amplification, or PSAPs) and hearing assistive technologies.
Hearing devices are more convenient and compatible than ever, with wireless connectivity to smartphones and lithium-ion rechargeable batteries, etc. All of this functionality have to take into account the fact that the device has to be as discreet as possible, which is mainly a question of size, that it needs to be operated by one hand only.
As a design question this has been successfully answered by Panasonic’s Side Push Switches. Since the height of the switch is first of all not above the PCB, designers can shrink the product or have additional space to work with.
The mid-mount design also means the PCB provides support for the switch, thereby improving the strength of the mount in relation to the direction in which the switch is pressed. Additionally, being able to mount the switch directly onto a PCB removes the need for a flexible or sub PCB for connecting switch and PCB, thus contributing to cost reduction in end product design.
A product is only as good as the sum of its parts; something especially crucial when it comes to designing safe and accurate medical devices and equipment. By taking these factors into account, design engineers can be sure they are choosing the best switches for their medical applications.:
