Steve, If it is, as you stated, of good quality and high purity, normally too much gold is not a problem for gold wire bonding. (However, it can be a reliability problem over time with aluminum wire but must here assume gold wire due to the thickness.) The heat sink is a potential problem depending on its mass. If the stage does not come to temperature there could be some bonding issues. Thermosonic bonding stages are normally operated at around 150C and most bonding schedules are target for that. As a quick check, you may wish to see if the quality if the last bonds are better than the first to get an indication (assuming here that the stage finally gets to temperature) This depends also on the size of the die and the number of wire bonds Too much temperature causing excessive softening of the flex adhesive or bonding adhesive and can result in acoustic dampening which could also cause some potential problems. Here the early bonds might be better than the latter ones. Again the size of die and number of bonds may have a time related influence . Just a few thoughts... Let us know what you ultimately learn. Kind regards, Joe