3D printed circuit boards: three technologies, three examples (Part 1)

HSMtec 3D pcb
Three-dimensional printed circuit board with HSMtec

Three-dimensional PCBs make optimum use of limited installation space and can be constructed using various processes, assembly variants and materials. With rigid-flex, semiflex and HSMtec 3D, we present three manufacturing processes and shed light on their technical properties, possible applications as well as their advantages and limitations.

Increasing packing density, reducing weight and at the same time increasing the reliability of assemblies – three-dimensional PCBs are being used in more and more products. The ability to directly connect parts of a circuit on different PCBs or PCB segments replaces connectors and cables. In addition, 3D PCBs open up new design possibilities and help to reduce system costs.

It is characteristic that the PCBs are laid out as a two-dimensional PCB, manufactured in the panel and assembled. Only after assembly is the PCB bent into its three-dimensional shape. A distinction is made between one-off bending for assembly, a few bends e.g. in use or constant bending e.g. for high bending cycles in use.

Rigid-flex printed circuit board: versatile geometries and layouts

Rigid-flex circuit boards are the preferred and optimal solution when several rigid circuit boards in different mounting positions and orientations are to be electrically connected. The parts of the circuit are distributed over several rigid circuit carriers and connected to each other via a flexible PCB foil made of polyimide. The flexible foil is integrated into the layer structure of the connected circuit boards. The flexible and rigid parts are electrically connected via. At the bending points, the FR4 material is milled away down to the flex foil. The thin polyimide guarantees maximum three-dimensional adaptability to limited space conditions. The space requirement of the PCB can be “folded away”, so to speak.

The rigid-flex technology is very versatile in terms of layout options and geometries. Further advantages: The elimination of many solder joints, cables, wires, jumpers and connectors not only minimises space and weight, but also eliminates potential sources of error and reduces overall costs. However, bending radii and bending cycles must be observed for the thin materials of the flexible PCB part.

Starrflex-Multilayer
Rigid-flex multilayer: The electronics for the Power-Check tool clamp are housed on a 4-layer rigid-flex multilayer that connects four rigid parts with one flex part.

One example: The compact housing of the Power-Check tool clamp from Ott-Jakob in Allgäu fits into the tool magazines of all machine manufacturers. The tool clamp checks the force with which the tool is pulled into the spindle cone of the machine tool. If the force falls below a certain threshold, there is a risk of increased tool wear or vibrations that leave unclean machining marks on a workpiece. The Power-Check checks not only the force: when setting up a new motor spindle, different tolerances for tools of different lengths can be simulated. In addition, digital switching outputs can be programmed for clear signal messages about whether a tool is well or poorly clamped.

The sophisticated design is realised in a four-layer rigid-flex multilayer – just 122.89 mm long and 70.15 mm wide – with an electroless nickel-gold surface, which connects four rigid parts with, among others, a flex part that lifts off. On it are, among other things, a microcontroller, a measuring device amplifier, several magnetic switches, LEDs for the display, a complete front end for radio transmission and a lithium cell as energy storage.

 
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