A method of bonding a metal ball for a magnetic head assembly is provided. Then, the client apparatus executes a biometric authentication based on biometric authentication method information notified from the server apparatus and encrypts the random number based on the private key. A threading device is associated with the rolls for an initial threadup of the yarn before the start of the process, and by which it is possible to lay the advancing yarn against the circumference of the rolls with a total looping greater than 360\xb0. Then, a polymer material including flux is placed on the surface of the solder bumps by a dipping process.