Molded Interconnect Devices May Be a PCB’s Partner in DesignSeptember 16, 2020 by Adrian Gibbons
Molded interconnect devices, when conditioned with laser direct imaging, could be a helpful 3D supplement to PCB design.
Harting recently made the bold claim that laser direct structuring (LDS) technology provides a method of electronic assembly without PCBs. LDS technology, which has taken on increasing popularity in recent years, works hand-in-hand with molded interconnect devices (also called MiD).
MiDs are injection molded rigid-body thermoplastics with special additives embedded in the structure of the plastics. When these plastics are conditioned by laser direct structuring (LDS), they allow metallization in an electroless copper bath to occur.
Laser direct structuring processes draw traces along MiDs, activating embedded additives, which are then built up to create conductive structures for PCB components.
Step-by-step outline of the LDS process. Image used courtesy of 3D-MID
LDS was invented more than twenty years ago at the Hochschule Ostwestfalen-Lippe University of Applied Sciences in Lemgo in partnership with LPKF Laser & Electronics AG. How has LDS/MiD technology developed since that time? And how might it complement traditional PCB design?
How MiD and LDS Supplement PCB Design
To answer these questions, it may be helpful to start with one company that uses LDS technology to create conductive traces on top of injection-molded parts. LPKF Laser & Electronics claims this process provides "a unique way of integrating mechanical and electronic functions on a molding."
The company explains that LDS and MiD technology combined offers reliable plated through-hole connectivity, allowing MiDs to incorporate two layers maximum. Molded interconnect devices are therefore not a replacement for traditional rigid PCB structures. However, when combined with LDS, these two technologies offer a host of benefits complementing traditional PCB design.
The LDS process includes 1) injection molding, 2) laser activation, 3) metallization, and 4) assembly. Image used courtesy of Laser Micronics
Some of these advantages include:
- More 3D design freedom
- Smaller and lighter designs
- Shorter process and decreased assembly times
- Lower costs upfront
- Integrated functionalities, such as antenna, connectors, sensors, and 3D conductive trace structures
Examples of MiD Applications
Examples MiD applications include hosted antenna structures, MEMS-sensor construction, and LED lighting applications, among others. Perhaps the most interesting application for MiD technology is its potential to replace flexible circuits.
Rather than designing a flex PCB, which will then later be adhered to molded plastic, MiDs offer a direct replacement option for certain applications. Image used courtesy of Harting
According to a Laser Micronics report, a sub-division of LPKF, molded interconnect devices offer free-form electronics design in rigid-bodies, reducing system components and weight. In automotive design, cable harnesses can be replaced with MiD technology, which reduces BOM complexity, improves reliability, and reduces costs.
Laser Micronics also demonstrates novel applications of MiD in medical equipment, like injection-molded hearing aids embedded with electronics. These devices offer more space and are lighter than traditional designs in standard form factors.
The question of power dissipation naturally arises when we are considering electronic components embedded inside an injection-molded structure, especially considering LED lighting. LPKF has developed "PowderCoating" with LDS additives, which makes the plastic electrically conductive and allows increased thermal control.
There are two variants of this technology: PES 200, which features high mechanical strength, and the PU 100, which is used for beneficial thermal properties.
Reimagining Antenna Design with LDS Manufacturing
A doctoral thesis published in 2019 by Aline Friedrich demonstrates one unique use case for testing with LDS manufacturing. The study conclusively demonstrated that a vehicle antenna system can be replaced by a mechatronic integrated device operating in the LTE cellular bands at 800 MHz and 1800 MHz.
Simulation of a MiD car antenna system for operating in the LTE frequency bands. Image used courtesy of the Leibniz Universitat Hannover (Aline Friedrich)
The thesis also goes on to explore additional areas that may be suitable for antenna installations, including non-metallic surfaces such as front and rear bumpers, side mirrors, front cowl, and rear tailgates. Most interesting is the approach to generate structures for FM band reception by using the metallic structures of the car as a ground reference to an embedded monopole.
PCB's Partner in Design
Engineers are always looking for ways to improve reliability, decrease cost, and push designs forward. Molded interconnect devices present an opportunity for such innovation.
While designers are used to thinking in planar 2-D worlds of the PCB, perhaps a mechanical-engineering perspective, like that demonstrated with LDS technology, can push EEs to see the world in 3D. Molded interconnect devices and laser direct structuring might just be the PCBs' new partner in design.