Micro Resistance Welding

One form of welding that is rapidly gaining in popularity as electronics and other devices continue to shrink is the process of micro resistance welding. This process is a thermal process, where the parts to be welded are heated to their melting points at their interface, and thus form one body when the weld cools. This process is nearly identical to the process of normal scale resistance welding although there are several differences and complications. The first of these is that the control systems must be much more precise in order to allow for the proper weld formation. A second complication because of the small size of the part, the oxide layer on it is much thicker in proportion than on a large scale resistance welded piece. Due to this special care must be exercised to remove the layer during the weld process. Lastly, is the increased difficulty of mating the parts in preparation for the weld.

How Micro Resistance Welding Works
To begin a micro resistance weld, the two parts are placed on top of each other above a copper alloy electrode. A second electrode is the brought down in this stack, using either a cable based foot petal or a pneumatic system, which compresses the two pieces together. Once the two pieces are squeezed together, a high electrical current is passed through the electrodes and through the parts at the precise intersect area. Because the contact area at the intersection is very small, the material heats rapidly when the current is turned on, melting both pieces where they contact. As soon as the energy is turned off, the molten zone rapidly cools and solidifies, forming a weld between the two pieces.

The most critical part of the process is the current and contact point. This electrical flow, which controls a sophisticated power supply, is not simply turned on then off after some period of time. Rather, the power supply provides a current that first ramps up to the desired amperage, then holds it there for a predetermined time before sloping back down to zero. The profile of this amperage curve is critical to the formation of a good weld and is formulated for each welding job.

Depending on the weld, it may be necessary to add other features to the current profile. One common addition is a long, lower amperage pulse before the main welding current is applied. This initial current helps to break down the oxide layers on the surfaces of the parts, leading to a much more consistent part interface. Due to this the weld is less affected by differences in the thickness of the oxide layer and is therefore more repeatable. It is also sometimes advantageous to modulate this initial pulse.  This creates a microscopic "scrubbing" action at the interface and further aids in the removal of the oxide layer. There are also many ways in which the main welding current profile can be altered, but they will not be discussed in this article.

Uses of Micro Resistance Welding
Micro resistance welding has countless applications in nearly all areas of manufacturing, including electronics, automotive systems, aerospace and medical devices. In the electronics field, micro resistance welding is a possibility whenever the need to quickly and efficiently weld small wires to each other or wires to parts, such as PCB pads. Examples of this include the production of sensors, lights, battery packs, solar cells and smoke detectors. Another  field in which micro resistance welding is growing in popularity is the automotive industry. In this field it is used for the production of lighting assemblies, electronic sensors, airbag systems and ignition controls. The aerospace industry uses micro resistance welding for such diverse applications as missile components, chaff, model fabrication and detonators.  Finally, the process is used in the medical field in many applications such as guide wires, cutting tools, pacemakers, hearing aids and much more. Micro Resistance Welding at Joining Technologies.

Joining Technologies employs micro resistance welding for a variety of applications in the sensor, electronic, instrumentation, and medical device manufacturing. Resistance welding is just one of many joining processes used at Joining Technologies  to address micro precision joining of ultra small electro mechanical assemblies. One of the most common applications for MRW is wire connections. In some cases MRW can be used  to simply hold components in place prior to being joined by another fusion energy process.

In conclusion, micro resistance welding is low cost viable option for joining small parts. It is fast, reliable, safe and clean, produces minimal fumes and has a relatively low cost per joint, due to its lack of consumables and  minimal electricity requirements. These advantages make micro resistance welding ideally suited for many of your joining needs.