Advanced joining techniques combine best of common methods to target high-speed, high-performance cable assemblies.
BY KRIS NIPPANI and WILLIAM TKAZYIK
To keep up with data transmission speeds found within the latest high-speed serial interfaces, such as InfiniBand, Fibre Channel, and Gigabit Ethernet, interconnect technology processes need to step up to the next level.
There are three common types of performance attachment methods for conductor-to-connector termination. The first, direct weld (Figure 1), is the direct attachment of the conductor to the connector terminal through the use of high current that causes enough heat to allow the two metals of the conductor and terminal to mix and form one homogeneous material between them.
 FIGURE 1. In direct weld termination, high-current heat causes the metals of the terminal and conductor to form one homogenous material. |
The electrodes are configured such that the positive electrode comes in contact with the wire, and the negative electrode comes in contact with the terminal. When all come in contact, the circuit is complete, and current flows to form the weld.
This method provides for an exceptional, easily repeatable, precise and highly reliable connection.
The second method, hot bar (Figure 2), is a solder re-flow technique using a single, one-piece metal bar (“hot bar”) that comes in contact with all conductors that are to be terminated at once. The conductors and solder on the underlying printed circuit board (PCB) are heated until the solder re-flows and forms a proper solder joint.
 FIGURE 2. In the hot bar solder re-flow method, a one-piece metal bar comes in contact with all conductors for a mass-termination technique. |
When properly fixtured, this mass termination technique allows for a significant labor savings over traditional single-point soldering methods, while still providing the same mechanical integrity.
 FIGURE 3. Parallel gap termination is often used to attach conductors to PCB pads, which are then soldered to a connector. |
The third method, parallel gap (Figure 3), is typically used to attach conductors to pads of PCBs, which are in turn soldered to a connector made for PCBs. Due to the configuration of a PCB termination area, the electrodes must be located side-by-side instead of opposite each other, as in the direct weld method. Parallel gap also serves to weld the conductor metal and PCB pad, resulting in a highly reliable connection over traditional soldering.
Attaching for high speed
We have created our own performance attachment variation, called direct attach technology. Through this method, which seeks to meet present and future high-speed data transmission requirements, a greater mechanical and electrical integrity can be obtained.
A significant aspect of this proprietary method is in the preparation of the conductors. In-house tooling capabilities provide for fixturing of all conductors into a “ribbonized” configuration. A laser-stripping operation is then employed, which has the ability to match the cable conductor’s configuration.
This process provides for the necessary minimal strip lengths without damage to the wire surface or excessive deformation to the conductor’s insulating material. Other stripping methods, such as manual, chemical, thermal, or semi-automatic wire stripping, do not provide the same precision and may damage the wire and/or shielding, thereby sacrificing electrical and mechanical performance.
With direct attach technology, today’s standards are surpassed by combining the best of the abovementioned three methods into one efficient, highly reliable, interconnect system. Some of the biggest advantages of direct attach technology are:
- Extremely low signal propagation delay mismatches;
- Minimal impedance discontinuities and corresponding unwanted signal reflections;
- Higher speed operation;
- Improved insertion loss;
- Consistent, reliable, high-integrity mechanical terminations;
- IPC Class 2 and ANSI J standard compliance.
Wire harness-friendly
Direct attach technology meets the requirements for cable and wire harness assemblies as defined in IPC/WHMA-A-620 and the ANSI-J Standard Requirements for Soldered Electrical and Electronic Assemblies. A wide range of common connectors can be used with this technology, including LFH, SCSI, HDM, VHDCI, MICRODOT, and MicroGigaCN. These interconnects are essential to such industries as high-performance computing, medical equipment, military and aerospace, high-resolution video, industrial electrical/electronic control, network storage and switching, and general data communications.
The methods of electrical connections have evolved over the years from crimping wires to contacts, forcing the insulation out of the way (insulation displacement), to manual hand soldering, to the semi-automated processes discussed here. Today’s application requirements demand the best of all worlds, and we believe that direct attach technology meets that need.
The “lower tech” methods still have their place under certain conditions and requirements, but when it comes to high-speed cables and connector technology, direct attach technology can be your wisest choice.
KRIS NIPPANI is senior applications engineer, and WILLIAM TKAZYIK is applications engineer at C&M Corporation, Wauregan, CT. (www.cm-corp.com)
