19. 06. 2017
MID in pole position
Three-dimensional molded interconnect devices
Three-dimensional molded interconnect devices (MID) are a welcome addition to conventional printed circuit boards and are particularly well suited to Industry 4.0 applications. The example of a smoke detector illustrates how design and functional integration are simplified with this technology.
Whether rigid or flexible, printed circuit boards are a virtually indispensable part of electronic devices as interconnect devices. Plastic molded interconnect devices (MIDs) offer many advantages with regard to connection technology including the combination of electrical and mechanical functions in a single component. This makes it possible to use the housing and other molded inner structures as an interconnect device and sometimes eliminating the need for a PCB.
Three-dimensional functional integration
The MID is a multifunctional component with sensors arranged and aligned with a high precision combined with an RFID antenna for sending and receiving signals. This concentration of functions on a single carrier material enables development engineers to create three-dimensional microelectromechanical systems (MEMS). MIDs are ideally suited for this purpose, particularly when manufacturing large and very large volumes.
MID technology in detail
Three-dimensional MIDs are manufactured using the LDS (laser direct structuring) method. The shape of the interconnect device desired by the customer is created in a single-component injection molding process. This offers virtually unlimited freedom for three-dimensional design.
While conventional printed circuit boards use FR4 fiberglass fabric or similar base material, molded interconnect devices are built from thermoplastics. The thermoplastic base material is first compounded with a (nonconductive) laser-activated metal-organic additive.
The LDS laser beam structures the circuit pattern onto the device by cleaving the metal-organic additives while roughening and ablating the plastic precisely where the beam strikes the surface. Copper seeds split out from the additive, attracting free copper in the subsequent metallization step.
In the following electroless metallization process within a copper bath the copper seeds created in the lasering step now attract solid copper out of solution. After copper plating, electroless nickel and immersion gold (ENIG) layers may be added to the copper layer. When an MID is not soldered or bonded, nickel alone over copper is sufficient. ENIG metallization ensures good surface properties for designs where SMT soldering or Wire-Bonded component placement is desired.
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