Welding structure, wiring board with metal piece, and welding method

A wiring board with a metal piece comprising:

• a flexible printed circuit comprising:
• a wiring pattern;
• and
• a base and a coverlay that sandwich the wiring pattern;
• and
• a metal piece welded to the wiring pattern,
• wherein the wiring pattern has a hole that passes through the wiring pattern in an up-down direction in which the flexible printed circuit and the metal piece are superimposed,
• wherein the flexible printed circuit is disposed on an upper surface of the metal piece,
• wherein the metal piece comprises a nugget portion where a part of the metal piece has been melted by heat of laser light that is irradiated from above and has re-solidified,
• wherein a peripheral portion of the hole in the wiring pattern covers the nugget portion, and
• wherein a part of the nugget portion is exposed through the hole.

A welding method comprising:

• a preparation step of superimposing a first metal member on an upper surface of a second metal member, wherein the first metal member has a hole;
• a fixing step of fixing the first metal member and the second metal member with a jig;
• and
• an irradiation step of applying laser light near the hole from above through a jig hole that is disposed in the jig and welding the first metal member and the second metal member, wherein
• in a top view, a trajectory of the laser light in the irradiation step is annular from a first point outside the hole to a second point inside the hole, and
• 0<R2<D1÷2<R1<D2÷2 is satisfied where a diameter of the hole is represented by D1, a diameter of the jig hole is represented by D2, a distance between a central axis of the hole and the first point is represented by R1, and a distance between the central axis and the second point is represented by R2.