Learn about improvements in print quality and innovations in substrates
What’s in store for the next generation of medical sensors and electrodes? In all likelihood, we’ll see the incorporation of several of the design features and performance attributes currently found in wireless communication devices: wireless transmission and receipt of data, incorporation of batteries and application-specific integrated-circuit (ASIC) chips for device management, and displays that will indicate the physiological status of the patient.
Attributes such as these are expected to be used in combination with cell phones or central receivers that incorporate application-specific programming. In addition, sensors are expected to be low profile, unobtrusive, small, lightweight, inexpensive, and highly flexible to conform to body motion. That is a lot to ask for in a market that is highly cost competitive and necessarily risk adverse. And who will promote the technologies and drive their growth? Look for the big push to come from cell-phone and Internet-service providers.
As medical practices and monitoring move away from the office environment to the home and the complexity of data collection and analysis grows, the features listed above will grow in importance to the patient and practitioner. This article describes how industrial-printing specialists are meeting changing demands.
Areas of development
Screen printing is commonly used to print electronic circuits onto a variety of flexible and rigid substrates. Presses are typically located in Class 10000 clean rooms designed to minimize particulate contamination and improve manufacturing yields. A representative example of a screen-printing setup is shown in Figure 1.
Printed circuits are often deposited onto plastic films or laminates, but recently interest in direct printing onto foam substrates has found favor with medical OEMs. Most circuits require both conductive and dielelectric materials. The conductive materials measure current as an indirect measure of a physiological response. Dielectric materials separate and protect the conductive trace layers.
A variety of conductive inks are available, but silver, silver/silver chloride, and carbon inks are generally used. The silver inks are made by the incorporation of silver-flake particles into an appropriate resin dissolved in solvent. Ratios of conductor to resin vary depending on the application and required conductivity levels. In addition, silver chloride salts are incorporated to provide both electrical and ionic conductivity. The ratio of silver to silver chloride can also vary depending on the application. Electrical conductivity levels are usually in the range of 0.1 ohms/sq.
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