An apparatus and method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame. The core is made of a material obtained by molding under heat a rubber composition containing a base rubber containing polybutadiene having a stress relaxation time, an unsaturated carboxylic acid andor a metal salt thereof, and an organic peroxide. A sample may be expelled from a sample holder using a piston that moves from a lower portion to an upper portion of the sample holder.