Method for producing flexible printed wiring board

A method for producing a flexible printed wiring board using a photoresist, comprising:

• placing the photoresist, including a first region and a second region, on a substrate;
• placing a first photomask including a first light-transmitting portion such that the first light-transmitting portion faces the first region to expose the photoresist through the first light-transmitting portion;
• and
• placing a second photomask including a second light-transmitting portion such that the second light-transmitting portion faces the second region to expose the photoresist through the second light-transmitting portion, wherein
• the first region is adjacent to the second region such that an edge portion of the first region overlaps an edge portion of the second region,
• the first light-transmitting portion has a linear shape including a first tip having a tapered shape,
• the first tip comprises:
• a first edge portion;
• a first curved side connected to the first edge portion;
• and
• a second curved side connected to the first edge portion and facing the first curved side,
• the second light-transmitting portion has a linear shape including a second tip having a tapered shape in an opposite direction to the first tip,
• the second tip comprises:
• a second edge portion;
• a third curved side connected to the second edge portion;
• and
• a fourth curved side connected to the second edge portion and facing the third curved side,
• the placing of the first photomask comprises placing a first alignment target point in the first tip at a first position,
• the placing of the second photomask comprises placing the second photomask such that a second alignment target point in the second tip overlaps the first position,
• the first alignment target point is separated from the first edge portion by a first distance on a first center line extending in a first longitudinal direction through a center of the first light-transmitting portion,
• the first and second curved sides are outside a first virtual triangle,
• the first virtual triangle is formed by connecting a first intersection between the first center line and the first edge portion, a second intersection between a first virtual line and the first curved side, and a third intersection between the first virtual line and the second curved side,
• the first virtual line extends along a first width direction of the first light-transmitting portion and passes through the first alignment target point,
• the second intersection is separated from the third intersection by a second distance,
• the second alignment target point is separated from the second edge portion by the first distance on a second center line extending in a second longitudinal direction through a center of the second light-transmitting portion,
• the third and fourth curved sides are outside a second virtual triangle,
• the second virtual triangle is formed by connecting a fourth intersection between the second center line and the second edge portion, a fifth intersection between a second virtual line and the third curved side, and a sixth intersection between the second virtual line and the fourth curved side,
• the second virtual line extends along a second width direction of the second light-transmitting portion and passes through the second alignment target point,
• the fifth intersection is separated from the sixth intersection by the second distance, and
• Δ
• ⁢
• x
• <
• A
• <
• Δ
• ⁢
• x
• +
• D
• -
• 2
• ×
• Δ
• ⁢
• y
• ×
• cos
• ⁢
• θ
• 2
• ×
• sin
• ⁢
• θ
• is satisfied
• where
• Δx is an amount of deviation of the second alignment target point from the first position in the first longitudinal direction,
• Δy is an amount of deviation of the second alignment target point from the first position in the first width direction,
• θ is an amount of deviation of the second alignment target point from the first position in a rotational direction around a first normal line passing through the first position and perpendicular to the first photomask,
• A is the first distance, and
• D is the second distance.