A molded interconnect device is an injection-moldedthermoplastic part with integrated electronic circuit traces. The use of high temperature thermoplastics and their structured metallization opens a new dimension of circuit carrier design to the electronics industry. This technology combines plastic substrate/housing with circuitry into a single part by selective metallization.
Applications
Key markets for the MID technology are consumer electronic, telecommunication, automotive and medical. A very common application for MIDs are integrated antennas in cellphones and other mobile devices including laptops and netbooks.
Manufacturing methods
Molded interconnect devices are typically manufactured in these technologies:
Laser Direct Structuring (LDS)
The LDS process uses a thermoplastic material, doped with a metallic inorganic compound activated by means of laser. The basic component is single-component injection molded, with practically no restrictions in terms of 3D design freedom. A laser then writes the course of the later circuit trace on the plastic. Where the laser beam hits the plastic the metal additive forms a micro-rough track. The metal particles of this track form the nuclei for the subsequent metallization. In an electroless copper bath, the conductor path layers arise precisely on these tracks. Successively layers of copper, nickel and gold finish can be raised in this way. The LDS process is characterized by:
flexibility: for a changed routing of traces, only new control data have to be transmitted to the laser unit. Thus different functional components can be produced from one basic unit
precision: finest conductor pathes with a width of < 80 µm are possible
prototyping: available LDS-coating of any part enables test specimen
Laser Direct Structuring was invented at Hochschule Ostwestfalen-Lippe, University of Applied Sciences in Lemgo, Germany, from 1997 until 2001. LDS technology was developed in a research cooperation with the former LPKF Limited, patented by the inventors and first exclusively licensed to LPKF. In 2002 the patents concerning LDS technology were transferred to LPKF Laser & Electronics AG. The major drawbacks of LDS are the need for the expensive metallic inorganic compound for the entire mold, the necessity for a chemical plating process, a very rough surface of the plated layer making connectors difficult to achieve. The created circuitry usually is limited to only one layer of wiring without crosses.
Printed Electronics
Selective metallization can be achieved by printing of conductive traces onto the surface of the thermoplastic part. Aerosol jet, inkjet, or screen printing may be used, whereas aerosol jet printing delivers the most reliable results on an arbitrary shaped mold. The main advantages to PE include:
any polymer can be used for injection molding
no metallic inorganic compound is necessary, which reduces cost
large variety of conductive coating materials including silver, copper, gold, platinum, graphite, and conductive polymers
thickness can be tightly controlled
direct deposition without plating possible
more complex circuitry possible as isolation layers, dielectrics, and other materials can be deposited in multiple layers
Currently, printed electronics is still a research and development area but an increasing number of companies start production of smart phone antennas and substitute LDS on other injection-molded parts. The major drawback is a low level of standardization because of the versatility of the technique.
Two-shot molding
Two-shot molding is an injection molding process using two different resins and only one of the two resins is platable. Typically the platable substrate is ABS and the non-platable substrate is polycarbonate. In a two shot component, these are then submitted to an electroless plating process where the butadiene is used to chemically roughen the surface and allow adhesion of a copper primary layer. The plating chemistry can be controlled to prevent the roughening of the polycarbonate portions of the component. While not commonly found outside of cellphone antenna production, this technology is public and widely available.
Placement of components onto the 3D body can be done in any mCAD software. There is a special design software available which can read in mCAD data as well as electrical CAD data including the net list. This tool offers interactive routing on the 3D surface as well as an online design rule check. Data can be exported in a LPKF production file. Also some PCB CAD software start offering 3D-MID design capability, like e.g. Target3001!.
