Introduction

Thermosonic ball bonding is the most common and cost effective method for general use on modern ICs.

  1. 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)
  2. 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
  3. The capillary is lowered onto the pad and squishes the ball onto the pad. Ultrasound and heat are used to form a solid connection
  4. 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

First bond

Overhead shots typically look like this (Photobit camera sensor, focal plane on pad)

ball_bond_01_neo20x_cropped.jpg

or this (focal plane on ball)

ball_bond_02_neo20x_cropped.jpg

Angled SEM image of ball bond (Samsung 16-mbit DRAM). Image copyright 1998-2009 Smithsonian Institution; used by permission.

ball_bond.jpg

Second bond

Test bonds on gold package pad (from AZ's training)

Capillary cleaning

SPT Capillary Unplugging Wires (CUW) tool

https://patents.google.com/patent/US20020096187A1/en

  • 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

https://www.ebay.com/itm/CROSSHAIR-WIRE-FINE-TUNGSTEN-WIRE-FOR-SCOPES-AND-TRANSITS-0125mm-0005/321070292094?hash=item4ac147dc7e:g:v-wAAMXQ2UVQ9N2j

  • 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
 
bonding/ball.txt · Last modified: 2018/04/28 14:18 by mcmaster
 
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