Backside surface welding system and method

A method for laser welding a first metal substrate to a second metal substrate, the first metal substrate having a first planar surface and a second planar surface disposed opposite the first planar surface, the method comprising:

• selecting first and second metal substrates having a thickness, surface tension and thermal characteristics suitable for controlled flow thereof when in a molten state;
• placing an end face of the second metal substrate proximate to the first planar surface;
• generating an input laser beam from a fiber laser,
• providing a beam delivery system configured to receive the input laser beam and to generate an output laser beam having a beam spot that moves in a predetermined pattern along a first and a second axes;
• and
• passing the input laser beam through the beam delivery system to irradiate a target area on the second planar surface of the first metal substrate with the beam spot, the target area positioned over an intersection region of the first planar surface where the end face is positioned proximate to the first planar surface.