Abstract: A bonding method includes attracting and holding a first substrate by using a first holder; attracting and holding a second substrate by using a second holder; and forming a combined substrate by moving the first holder and the second holder relative to each other to bring the first substrate and the second substrate into contact with each other. The bonding method includes heating the first substrate and the second substrate or the combined substrate; and cooling the heated combined substrate by using a cooling unit. In the cooling, bending of the combined substrate is controlled by forming a temperature difference in the combined substrate.

Abstract: A method of circulating an electroless nickel plating solution is characterized in that the system comprises the following process steps effected in the following order: (A) a step of electrolessly plating nickel using a plating solution having nickel hypophosphite contained as a chief chemical material for supplying a plating metal ion Ni2+ and a hypophosphorous acid ion H2PO2− acting as a reducing agent; (B) a step of removing HPO32− from a plating solution that has aged in the step (A); (C) a step of desalting the mother liquor separated from the step (B); and (D) a step of adjusting the components of the treated plating solution and then circulating same back into the step (A) of electroless nickel plating. According to the present invention, the plating solution is free from the formation and accumulation of a sulfuric acid salt and hence a long service life is ensured and a great advantage in environmental protection is provided.