Reliability in Medical PCBs
Whether you are creating a wristwatch that keeps track of blood pressure or heart rate, or an insulin pump, medical PCBs must be both flexible and durable. These devices are constantly subjected to vibration, flexing, and bending while also needing to withstand moisture, chemicals, shock, and other environmental conditions. As a result, medical PCBs are becoming increasingly tinier and require finer lines and spaces along with thinner copper and base material. This leads to the need for a specialized flex circuit that can withstand these conditions and still provide reliable functionality.
Unlike rigid boards, which use a fiberglass substrate that is impregnated with epoxy resin, flex circuit pcb have a base made of a thin layer of flexible plastic. The most common choice is polyimide. It is a very tough material that can withstand repeated flexing without damage, and it is tolerant to heat from solder reflow and expansion and contraction due to temperature fluctuations. It also can withstand multiple reflow cycles and has a low melting point that prevents hot spots in the board.
The flex substrate also requires an additional layer of flexible plastic, known as coverlay, to insulate the outer surface conductors and protect them from corrosion and damage. This is commonly a layer of PI, although it can be made from PET or a flexible-epoxy-and-glass-fiber core. Manufacturers used to attach these layers with adhesives, but this led to increased stress in the traces and connections. To avoid this, manufacturers developed adhesiveless PI that attaches to the copper of a flex circuit directly.
How to Ensure Reliability in Medical PCBs
Copper is a highly conductive metal, but it is also prone to fatigue. As a result, if your flex circuit will be subjected to repeated flexing and bending, you need to consider the use of higher-grade rolled annealed copper foil. This will increase the amount of stretch before fatigue cracking sets in and will improve flex durability by providing greater springiness in the Z deflection direction.
Flex circuits are also useful for reducing package size and weight, as they can be folded or bent to fit in tight areas or around complex geometries. This makes them ideal for medical gadgets that need to conform to specific sizes and styles, such as wearable sensors and invasive devices that must be placed into patients’ bodies.
Ensure reliability in your flex or rigid-flex circuit by selecting the best materials for the job and collaborating with a manufacturing partner that can deliver high quality products on time and budget. By using PCB layout software and simulation tools, you can verify the design for fabrication and test to make sure that your flex circuit meets project requirements. Using Altium Designer on the Altium 365 platform gives you access to the full range of features and automation tools you need to get your design off the ground quickly. Try it for free today.
