Ball at end of melted wire

Guest

i read in one of your forums about eos with a 'ball' forming on one end of the melted wire. i think i saw this in one device about a month ago. does this ball mean anything? why is this ball formed? thnks.

device engr

Joined: 20 Jun 2026 Posts: 76

Hi Device Engr,

Whenever a wire melts and breaks in the middle, a ball is usually formed on the more positive end of the wire. A ball is formed because this shape (spherical) gives the molten end the state of lowest energy before it cools down and solidifies. Also, the ball is formed closer to the die if the bonding post is a better heatsink, or closer to the post if the die is a better heatsink.

Thus, the location of the ball tells you the direction of the eos current, since the ball is formed on the more positive end. It also tells you which conducts heat better, the die or the bonding post/finger.

FARel Engr