A method for estimating a direction of arrival of a signal transmitted by a signal source and received by an antenna array. To detect whether the pick-up tool has gripped the semiconductor chip, a body with a reflecting surface is arranged in the longitudinal drill hole of the pick-up tool which, when passing over the light source on absence of the semiconductor chip deflects light shining from underneath into the longitudinal drill hole of the pick-up tool into a horizontal plane. Likewise, should the male mold section be used in downstream processed, the pick and place unit is operable to engage and lift the male mold sections and place them in an associated male mold pallet. Each broker maintains subscription information in the form of a directed acyclic graph and a broker vector. With this configuration, it is possible to prevent the shift of a threshold voltage Vth, and hence to enhance the reliability of the transfer or reset of electric charges.