In addition to saving space, this enables direct integration of IC chips and small surface-mount devices (SMDs) into the molded housing. It also allows for the creation of recesses, channels, and openings for sensors, and contact elements. Three different processes are typically used in creating MID assemblies.
Two-shot molding is a two-stage injection molding process using two different plastic compounds, one of which can be metalized to create conductor paths, while the second compound is inert to plating agents. Minimum line widths and spacing are around 400 μm.
LDS uses laser beam to define electrical conductor paths and functional features. The beam selectively activates metal additives in a molded polymer to allow plating of the conductor paths with minimum line widths and spacing down to 150 μm.
In LSS, an entire surface is chemically activated and metalized. The electrical structure is created through laser ablation and subsequent separation of the tracks by etching. Dimensional resolution is about the same as in LDS.
The processes most commonly used in MID assemblies are wire bonding, flip-chip mounting, and attachment with conductive adhesive. MID devices can also be created with connection pads for surface mounting to a circuit board.
In addition to final packages with a reduced height and footprint, circuit components and traces can be easily integrated with I/O connectors to create an assembly that becomes the finished device package. Conductive traces can be created to take on shapes that allow them to function as antennas, heaters, shielding, and switch contacts.
Hybrid connectors are a recent development that allows mixed transmission media, such as power, control signals, data communications, and pneumatic lines in a single connector housing. This eliminates the need for multiple connectors for different purposes, shrinks the overall size of the finished product, and lowers costs. Other features have been added to improve functionality, reliability, and safety.
An example of this new type of connector is used in a laser hair removal instrument created by Lutronic Cor por ation, Fremont, CA, which required FDA approval before being commercialized. The design of this instrument involves a handheld laser wand connected to a table- or floor-mounted power and control unit. One design challenges was to figure out the best way to run power, control signals, and cooling water from the main console to the laser head.
Major design criteria included a streamlined look with compact external connections that would be easy to connect and disconnect the laser head from the console. For Lutronic to develop a custom connector with these features would have required a difficult and lengthy engineering project. Therefore, its engineers looked for an off-the-shelf connector that could be modified to incorporate all the instrument’s electrical/ electronic interface wiring, plus laser head cooling water connections. They found it in HARTING’s Han-Yellock® connector line. (See Figure 2)
In the Han-Yellock connector, a variety of inserts are available to carry power, data communications, signal wiring, and air for cooling or control. In Lutronic’s case, the pneumatic functionality was modified to carry cooling water to the laser head. Based on earlier Lutronic designs of small cooling water connection components, this functionality was a relatively easy addition to the Han-Yellock housing. To avoid the possibility of water leakage into the electrical connections, which wasn’t an issue with a pneumatic insert, Lutronic engineers designed a solid separator wall to isolate the water from the electrical side of the connector.
Along with a mating bulkhead connector on the main console, this hybrid connection carries signals that control the temperature parameters of the laser, communicates the status of laser head control buttons and trigger assembly, and supplies cooling water to prevent the laser from overheating.
It also has a single-hand latching mechanism with audible and visual indicators of the locking status, which ensures a safe, solid connection of the laser headpiece and cable assembly to the console, and makes it easy to swap out laser heads. Another plus is cable production that does not require any special assembly tools, and availability of economical off-the-shelf hardware.