Surface Mount PPTC Device With Integral Weld Plate
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing surface mountable PPTC devices face damage from high temperatures required for resistance spot welding, leading to irreversible damage and detachment of battery/cell interconnect straps during reflow operations.
Innovation Solution
Incorporating a weld plate with sufficient thermal mass, typically made of pure nickel, to absorb welding heat without damaging the PPTC device, allowing for reliable mechanical and electrical connection of interconnect straps through micro spot welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistance spot welding is applied to attach interconnect straps to PPTC devices, then reliable mechanical and electrical connection is achieved, but the high temperature (1500°C to 1600°C) causes irreversible damage to the PPTC material
Solution Approach 1:
A weld plate made of high-melting-point material (such as nickel or stainless steel) is introduced as an intermediary between the interconnect strap and the PPTC device. The weld plate withstands the high welding temperatures (1500°C to 1600°C) without damage, while the PPTC material is protected from direct thermal exposure. The weld plate is attached to the PPTC device through a low-temperature process (such as soldering or eutectic bonding), allowing the strap to be welded to the weld plate without damaging the PPTC material.
2Object-affected harmful factors
If soldering is used to connect interconnect straps to PPTC devices, then the PPTC material is protected from high temperature damage, but the interconnect straps shift position or become detached during reflow operations
Solution Approach 1:
The weld plate serves as a mediator that provides a stable anchoring point for the interconnect strap through welding, while the connection to the PPTC device is established through a separate low-temperature process. This dual-connection approach ensures both thermal protection and mechanical stability, preventing strap detachment during reflow operations.
Solution Approach 2:
The connection process is segmented into two distinct stages: (1) attaching the weld plate to the PPTC device using a low-temperature process (soldering or eutectic bonding), and (2) welding the interconnect strap to the weld plate using high-temperature resistance spot welding. This segmentation allows each connection to be optimized for its specific requirements without compromising the other.
3Reliability
If high temperature adhesive or polymeric overmold structures are used to hold interconnect straps in place during reflow, then position stability is maintained, but the device complexity increases and additional materials are required
Solution Approach 1:
The mechanical holding system (adhesive or polymeric overmold) is replaced with a metallurgical bonding system. The weld plate provides a rigid, thermally stable platform that mechanically and metallurgically secures the interconnect strap through welding, eliminating the need for additional adhesive layers or polymeric structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables reliable attachment of interconnect straps to PPTC devices without damaging the polymeric material, maintaining the device's functionality and preventing detachment during solder reflow, thus providing a stable and effective electrical connection.
Implementation Method 1
providing the PPTC device with a weld plate having sufficient thermal mass to withstand the spot welding incident without damaging the PPTC material immediately opposite the weld location
Implementation Method 2
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
Data Source
AI summary
A surface mount circuit protection device includes a laminar PTC resistive element having first and second major surfaces and a thickness therebetween. A first electrode layer substantially coextensive the first surface is formed of a first metal material of a type adapted to be soldered to a printed circuit substrate. A second electrode layer formed at the second major surface includes structure forming or defining a weld plate. The metal weld plate has a thermal mass and thickness capable of withstanding resistance micro spot welding of a strap interconnect without significant resultant damage to the device. The device is preferably surface mounted to a printed circuit board assembly forming a battery protection circuit connected to a battery/cell by battery strap interconnects, wherein one of the battery strap interconnects is micro spot welded to the weld plate of the device.