Validating The Resistance Welding Process, American Welding Society Journal, December 2009 Issue

The resistance welding world encompasses a wide range of applications and part sizes.  Within this unique world, competition for securing new orders and retaining existing business is increasing, especially in a down economy.  One way to provide a competitive edge is to validate your resistance welding process.  The automotive and medical device sectors have a long history of using the validation process.  To ensure consistent resistance welding quality, the automotive companies require proof of resistance welding validation from their automotive sub-system suppliers.  In addition, the Federal Food and Drug Administration (FDA) requires medical device manufacturers to validate all processes used to manufacture a medical device.  Both sectors essentially employ the same validation process, but use different labels for each validation component.  While this article uses a battery pack example to illustrate the resistance welding validation process, this basic validation process is applicable to all resistance welding applications regardless of the part size.

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The size of the large scale resistance spot welding application market is easily an order of magnitude greater than small and Micro-Scale resistance welding applications. Large scale resistance spot welding is well over 100 years old and represents a mature joining process. These factors have driven the creation of welding tables that clearly define the large scale resistance spot welding process.   

Small and Micro-Scale resistance spot welding on the other hand is being fueled by the explosion to make everything smaller, from automotive electronics, to telecommunications components and medical products. The only thing that these applications have in common is their lack of commonality, making the creation of standardized welding tables almost impossible.

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FlashSoldering was first developed in 1998 as a new innovative, non-contact, localized reflow soldering process for terminating fine insulated copper magnet wires to electronic contacts without first removing the wire insulation.  Subsequent research in 1999 has extended FlashSoldering applications from miniature magnetic component packages to soldering insulated single and multiple magnet wires and Litz wire to high-speed data connectors and other forms of electronic contacts.  Quality issues concerned with copper-tin intermetallic growth and what happens to the magnet wire insulation during FlashSoldering were successfully resolved.  Applications for FlashSoldering have broadened to include: single and multiple toroidal transformer packaging; LAN filters; low power DC-DC converters; single or multiple form coils and inductors; woven or braided high speed data cables; and connecting a single wire to a Litz wire bundle.

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FlashSoldering is a new non-contact reflow soldering process specifically developed for terminating tine insulated copper magnet wire to a special electronic contact without the need for added solder or flux.  Two components comprise the FlashSoldering system.  The first component is a unique electronic contact used to locate and retain very tine insulated copper magnet wires during the soldering process.  The second component is a diode laser which is then used to simultaneously remove the insulation and reflow solder the wire to the contact without damaging or contacting the wire. 

Extensive testing using 100 micron (.004 inch) diameter heavy polyurethane-nylon insulated copper magnet wire has proved that FlashSoldering is a repeatable process. Additional testing will be necessary to determine the practical maximum and minimum magnet wire diameter range. Applications include terminating miniature toroidal transformers, DC-DC converters, LAN filters, and more.  The receptacle or lead frame is scaleable to production requirements.

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The electronics industry effectively uses mass reflow soldering techniques to bond the majority of through-hole and surface mount components to their printed circuit board (PCB) assemblies.  However, some temperature sensitive electronic components can not tolerate the high temperature peak of 230°C for one minute that is typically encountered in the mass reflow soldering process without suffering damage.  These components are soldered off-line using hand or other semi-automated soldering techniques.  This process is commonly known as "Odd Form Soldering" or "Selective Soldering" and constitutes as much as 10% of all electronic assembly work.

"FlashSoldering", using diode laser technology, is a new, non-contact, selective soldering process that offers the electronic component assembler a highly controlled method for soldering a variety of temperature sensitive miniature and micro-miniature components.

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