1. Field of the Invention
The present invention relates to electrical circuit components. More particularly, the present invention relates to a surface mountable polymeric positive temperature coefficient (PPTC) device including a weld plate to which a conductor strap interconnect, e.g. an interconnect suitable for battery packs, may be resistance welded, for example.
2. Introduction to the Invention
It is known to provide an electrical cell or battery protection circuit comprising a printed circuit board and a PPTC device, which is surface-mounted to the printed circuit board. An electrical circuit formed on the printed circuit board including the PPTC device functions to regulate within a safe limit the current flow from and/or to the electrical cell or battery. In this prior arrangement an interconnect strap from the cell or battery was typically connected to a foil electrode of the PPTC device by soldering. One example of this prior approach is disclosed in International Publication No. WO99/60637 (K.K.Raychem). Another example is shown in a commonly assigned U.S. patent application Ser. No. 09/923,598, published on Feb. 6, 2003, as patent application Publication No. US2003/0026053. The disclosures of these publications are expressly incorporated herein by reference.
One drawback of the prior approach such as that disclosed in the referenced publication is that the interconnect strap from the battery was soldered to the foil electrode of the PPTC device. In some cases, the interconnect strap was connected yet again to the printed circuit board. In such devices those battery/cell interconnect straps tended to shift position or become detached when the PPTC device was heated and soldered, e.g. by reflow techniques, to the printed circuit board. In order to maintain the battery/cell interconnect strap in place during reflow operations, it was found necessary to employ a high temperature adhesive material or to provide a high temperature polymeric overmold structure to hold the strap in place.
While it would be desirable to be able to weld a battery/cell interconnect strap or battery/cell electrode directly to the PPTC device, resistance spot welding techniques practiced by users of PPTC devices must generate sufficient local heating to melt the metal and thereby fuse the strap to an underlying electrode layer of the device. Heretofore, the high temperatures required for effective welding, on the order of 1500° C. to 1600° C., have resulted in irreversible damage, or destruction of physical properties and electrical characteristics, of the PPTC material. Thus, a hitherto unsolved need has remained for a surface mountable PPTC device to which a battery/cell electrode strap could be attached by welding.