Circuit board
Provided is a method of manufacturing a circuit board including preparing a board structural body ( 11 ) and covering a conductor circuit element ( 13 ) on an outermost layer of the board structural body ( 11 ) with a cover film ( 14 ), wherein a heat treatment is performed while having a release material ( 15 ) interposed between the cover film ( 14 ) and a heat-processing device. The release material ( 15 ) is a laminate at least including, sequentially from the cover film toward the heat-processing device, a low friction film ( 16 ) selected from an ultrahigh-molecular-weight polyethylene film and a polytetrafluoroethylene film, a first aluminum foil ( 17 ), a first high-density polyethylene film ( 18 a ), a second high-density polyethylene film ( 18 b ), and a second aluminum foil ( 19 ). The first high-density polyethylene film ( 18 a ) and the second high-density polyethylene film ( 18 b ) are positioned such that respective MD directions are perpendicular to each other.
1. A circuit board, comprising:
a board structural body comprising a board and a conductor circuit element disposed on a surface of the board; and
a cover film on a conductor circuit side of an outermost layer of the board structural body,
wherein:
the cover film comprises a film comprising a thermoplastic polymer capable of forming an optically anisotropic melt phase,
in a cross-section of a thickness direction of the circuit board, the board structural body is covered with the cover film at an approximately uniform thickness,
in the cross-section of the thickness direction of the circuit board, the conductor circuit element has an approximately rectangular shaped cross-section and the cover film covers the conductor circuit element in a laterally equal manner,
when the approximately rectangular cross-section of the conductor circuit element has a thickness t, the approximately rectangular cross-section is provided with four corners of a board-side left end part, a board-side right end part, a cover film-side left end part, and a cover film-side right end part, the cover film has a thickness t1 measured from the cover film-side left end part, a thickness t2 measured from the cover film-side right end part, and a thickness t3 measured from a cover film-side central part; and
deviation of a thickness (unit: %) of the cover film satisfies formula (1):
[Max( t 1- t 3)−Min( t 1- t 3)]/ t< 30 (1),
wherein Max(t1-t3) is a maximum value among the thicknesses t1 to t3 of the cover film, Min(t1-t3) is a minimum value among the thicknesses t1 to t3 of the cover film, and t is a thickness of the conductor circuit element.
2. The circuit board of claim 1 ,
wherein the conductor circuit element comprises a differential signal line, and
the board structural body is covered with the cover film at an approximately uniform thickness in the cross-section of the thickness direction of the circuit board.
3. The circuit board of claim 1 ,
wherein when the conductor circuit element comprises a first differential signal line and a second differential signal line,
the first and second differential signal lines respectively have thicknesses t a and t b in rectangular cross-sections of the first and second differential signal lines,
a rectangular cross-section of each of the first and second differential signal lines is provided with four corners of a board-side left end part, a board-side right end part, a cover film-side left end part, and a cover film-side right end part,
the cover film has a thickness t1 measured from the cover film-side left end part of the first differential signal line, a thickness t2 measured from the cover film-side right end part of the first differential signal line, a thickness t3 measured from a cover film-side central part of the first differential signal line, a thickness t4 measured from the cover film-side left end part of the second differential signal line, a thickness t5 measured from the cover film-side right end part of the second differential signal line, a thickness t6 measured from a cover film-side central part of the second differential signal line, and a thickness t7 measured from a central part between the first and second differential signal lines; and
deviation of a thickness (unit: %) of the cover film satisfies formula (2):
[Max( t 1− t 7)−Min( t 1− t 7)]/ t< 30 (2),
wherein Max(t1-t7) is a maximum value among the thicknesses t1 to t7 of the cover film, Min(t1-t7) is a minimum value among the thicknesses t1 to t7 of the cover film, and t is an average of the thicknesses t a and t b of the first and second differential signal lines.
4. A circuit board, comprising:
a board structural body comprising a board and a conductor circuit element disposed on a surface of the board; and
a cover film on a conductor circuit side of an outermost layer of the board structural body,
wherein:
the cover film comprises a film comprising a thermoplastic polymer capable of forming an optically anisotropic melt phase,
in a cross-section of a thickness direction of the circuit board, the board structural body is covered with the cover film at an approximately uniform thickness, and
a thermal expansion coefficient α C of the cover film is from −2 to +3 (×10 −6 /° C.) with respect to a thermal expansion coefficient α M of a conductor in the conductor circuit element.
5. A circuit board, comprising:
a board structural body comprising a board and a conductor circuit element disposed on a surface of the board; and
a cover film on a conductor circuit side of an outermost layer of the board structural body,
wherein:
the cover film comprises a film comprising a thermoplastic polymer capable of forming an optically anisotropic melt phase,
in a cross-section of a thickness direction of the circuit board, the board structural body is covered with the cover film at an approximately uniform thickness, and
an insulation material of the board comprises a thermoplastic polymer capable of forming an optically anisotropic melt phase.
6. A circuit board, comprising:
a board structural body comprising a board and a conductor circuit element disposed on a surface of the board; and
a cover film on a conductor circuit side of an outermost layer of the board structural body,
wherein:
the cover film comprises a film comprising a thermoplastic polymer capable of forming an optically anisotropic melt phase,
in a cross-section of a thickness direction of the circuit board, the board structural body is covered with the cover film at an approximately uniform thickness, and
a difference in dielectric constants between an insulation material of the board and an insulation material of the cover film is within +5%.