Thermosonic ball bonding is the most common and cost effective method for general use on modern ICs.
- The wire is fed through a ceramic capillary, shaped somewhat like the end of a cheap mechanical pencil (fat cylinder with a thin cylinder on the end)
- The tip of the wire is melted by an electric arc (negative electric flame-off or NEFO, the most common process) or hydrogen flame (in older bonders, or highly ESD-sensitive applications) and surface tension forms a ball
- The capillary is lowered onto the pad and squishes the ball onto the pad. Ultrasound and heat are used to form a solid connection
- The second bond (from the wire to the leadframe) is normally very similar to a wedge bond but has a semi-circular or ring shape as it is formed by the side of the capillary
Overhead shots typically look like this (Photobit camera sensor, focal plane on pad)
or this (focal plane on ball)
Angled SEM image of ball bond (Samsung 16-mbit DRAM). Image copyright 1998-2009 Smithsonian Institution; used by [[archive>smithsonian|permission]].
Test bonds on gold package pad (from AZ's training)
SPT Capillary Unplugging Wires (CUW) tool
- Haven't tested
- My capillary is something like 1.6 mil => 40 um => CUW-35 reccomended
- Note 1 mil wire => 25 um
- Pretty boring
- Says poke it with a wire, ultrasonically clean it, and maybe sand the tip
- Duh..this is what I tried before looking. Although I don't have a fine enough wire on hand
A few sources hint at methanol as the preferred cleaning agent
- CROSSHAIR WIRE FINE TUNGSTEN WIRE FOR SCOPES AND TRANSITS .0125mm/.0005"
- 0.0005 and 0.0015
- 3' lengths
- Smaller than I wanted, but eh lets give it a try since its so inexpensive