Putting them to work

Compression connectors can be better understood by looking at some successful applications:

• A handheld patient monitoring device (Fig. 3), such as for a multi-function, LCD module and battery connector.

FIGURE 3. This handheld patient monitoring device incorporates multi-function compression contacts for both power and signal functions.

The design challenge involves a single piece design that is capable of connecting an LCD display and two rechargeable batteries. Additional design criteria include the requirement to be compatible with automated assembly processes, and to have a high level of reliability, including shock and vibration.

The solution is to create a single-piece plastic housing that holds a battery compartment on one side, and a recess to hold the LCD module on the other. The customer’s assembly robot places the LCD module into the housing, then places the PCB over the locating posts integral to the connector, and heat-stakes the PCB in position, effectively attaching the LCD to the connector and PCB. This design eliminates the previously used battery wires and clips, as well as eliminates the soldering operation needed to attach the connector and LCD module to the PCB, thereby creating a cost effective solution.

• A portable medical imaging device, such as for a high-density, board-to-board-to-board interconnect.

The design challenge involves creating a high-density device that could couple three parallel PCBs with 592 I/O contacts in a 1.0-inch (25-mm) × 1.5-inch (38-mm) package (Fig. 4). The system needs to be highly reliable, as well as allow serviceability of the device (disassembly and reassembly).

Click here to enlarge image FIGURE 4. One of the dual 592 contact wafers, with alignment and attachment guides.

The solution is to create a compression micro-contact connector with nearly 600 contacts that can be accurately positioned and retained between each of the three PCBs. The contacts are gold-plated and insert-molded for a tight tolerance registration and low resistance connection. To create the precision outline, a post-molded laser-cut operation is performed to obtain the desired mounting options and alignment holes. Two low-profile stainless steel plates with mechanical screw locks are used to support the top and bottom PCBs to effectively create the PCB wafer system.

This compression micro-contact connector results in a high performance yet cost-effective solution that fits into the handheld scanner. The custom connector design lets the technicians remove the handheld device, disassemble the head for cleaning, and reassemble the device in the field.

• A portable fluid pump with a modular control unit. The device consists of a central modular unit that serves as a power and control unit. Auxiliary electronic application devices (i.e., patient monitoring or data recorders) can be attached or mounted to the central device as required. This application features a very robust, liquid tight, I/O (input/output) connector to connect external auxiliary units to the main control module.

The design challenge involves requiring a connector that enables both power and signal circuits to run between the central module and the add-on auxiliary units. Additional criteria includes eliminating external cable assemblies, reducing system cost, allowing attachment of the auxiliary units by non-technical users, having a sealed system, and incorporating early mate and late break grounding features.

The solution is to design a custom male-to-female bracket that has a built-in compression contact connector incorporated (Fig. 5). To add a module, the nurse places the male bracket of the auxiliary unit into the female bracket on the center control module, which allows the auxiliary unit to rotate down into final position. As the bracket rotates, compression contacts press against mating contacts in the other bracket, make the electrical connection, and lock the two units together.

FIGURE 5. The compression-on-compression interconnect method, with hinge/lock mounting bracket.

The contacts in the bracket are well protected from damage and are sealed against spray-on disinfecting cleaners, allowing an auxiliary unit to quickly attach to, and be retained by, the main control unit without additional costly or cumbersome mechanical hardware. This design consequently makes all necessary electrical connections to run the system, both transportable and seamless to the user.

Compression connector technology offers the medical device designer many valuable advantages. When coupled with the advances in computer automated design techniques, contact material selection, improved insert molding techniques, and rapid prototyping processes, compression contact connectors are giving medical device designers a multitude of new options to help create higher performance and user-friendly devices.