DAVID FROMM, Chief Operations Officer, Promex Industries, Inc.
Looking ahead to 2025, a rapidly accelerating trend is the proliferation of complex assembly directly onto flexible substrates. We are seeing heightened demand from customers for flex assembly capabilities. Two years ago, about 10% of our customer inquiries were related to flex projects. Today, this figure has soared to 70-80%. In addition, requested assemblies incorporating flexible circuit boards are becoming increasingly complex, with chip-on-flex and other complex assemblies incorporating non-surface-mount components. Flex circuits offer many more product design opportunities than rigid circuits, but they also pose additional, different challenges. As a result, they are changing the required equipment set and workflows required to build these complex devices.
Demand for flex stems from using sensors and/or actuators as the core technology to enable the network proliferation of information-gathering devices that are connected to the cloud via an internet router (typically a cell phone or the like); flex enables more compact and durable devices. Frequently, the form of the device needs to be adjustable so that sensors can be positioned where they are needed. These use cases introduce a new variable into the assembly process: the circuit must be able to move during assembly, use, or both, putting increased mechanical stresses onto interconnection joints within flex-circuit devices.
This factor must be considered when devising an assembly solution. Creating a reliable joint requires limiting motion in the Z direction and curling of the flex substrate during assembly along with employing different encapsulant and underfill materials with unique mechanical properties to accommodate motion in the final device while protecting delicate electrical and mechanical joints. Both of these challenges require careful design of processes, fixturing, and tools used for assembly.
Why is flex demand growing now? Fabrication technology, particularly lithography, required to create high-density circuits on flex has greatly improved, with circuit density rivaling that of rigid substrates; commercially available flex has trace densities as low as 25-micron lines/spaces, moving down to 10 microns. Accordingly, product designers are pursuing chip-on-flex, high-density flip-chips on flex, wire bonding to flex – essentially, doing virtually anything with flex that they can do with rigid substrates.
The rise of assembly on flex is benefiting many applications – from wearables and implantable medical devices, to automotive and aerospace systems; Mars Rover units contain high-technology rigid-flex as well as extended-length flex circuit technology. This is pivotal for advanced semiconductor packaging, where maximizing functionality within a small footprint is essential. Material requirements are also evolving; implantable and wearable devices require bio-compatible materials, creating further assembly challenges with fewer material choices available.
Flexible circuit technology’s ability to conform to the shape of things that need to move eliminates connectors, which can fail or break. Flex offers high durability and robustness and is far less susceptible to thermal cycling fail than rigid circuits incorporating connectors. We anticipate continued high demand for our contract manufacturing capabilities, enabled by the knowhow of our skilled engineers and assembly experts.
Click here to read the 2025 Executive Viewpoints in Semiconductor Digest
