Substrate, printed wiring board, and semiconductor package

A substrate comprising:

• a metal clad laminate including a metal foil and a cured product of a prepreg;
• and
• an insulating layer laminated on at least one surface of the metal clad laminate,
• wherein the metal clad laminate has 400 μm or more of an average thickness T1 measured by the following method using a laser displacement gauge and 10 μm or less of an absolute value D1 of a difference between a maximum value and a minimum value of a thickness,
• (Method for measuring the average thickness T1 and the absolute value D1 of the difference between maximum value and minimum value of the thickness of the metal clad laminate):
• In a plan view of the metal clad laminate, four rectangular thickness measurement regions each having a vertical length of 60 mm and a horizontal length of 60 mm are set at any positions not overlapping each other;
• In the rectangular thickness measurement region, a vertical measurement line is set to twelve lines every 5 mm from a position 2.5 mm away from a left side, and on each vertical measurement line, thickness measurement is performed at intervals of 1 mm in a longitudinal direction with a starting point of less than 1 mm (however, not 0 mm) from an upper side;
• In addition, in the rectangular thickness measurement region, a horizontal measurement line is set to twelve lines every 5 mm from a position 2.5 mm away from the upper side, and on each horizontal measurement line, thickness measurement is performed at intervals of 1 mm in a horizontal direction with a starting point of less than 1 mm (however, not 0 mm) from the left side;
• and
• An absolute value of a difference between a maximum value and a minimum value of the thickness is calculated for each of the four thickness measurement regions, and a value obtained by averaging the absolute values is set as the absolute value D1 of the difference between the maximum value and the minimum value of the thickness, in addition, an average thickness of all the points in the four thickness measurement regions is calculated, and this average thickness is set as the average thickness T1 of the metal clad laminate.