Study On The Crater Issue In Thin Al Pad Of Die During Copper Wire Bonding Process

The copper wire as one kind of wire bonding materials has attracted more and more attentions in package industry due to its low cost and good conductivity.However,crater defect during bonding process was easily found when wire bonding was out of control because the copper wire was hard and oxidizable.For the aluminum pads on discrete semiconductor dies,the thickness of aluminum was gradually reduced from 4?m to less than 2?m due to the market requirement.So the control method and parameter optimization in copper wire bonding process for discrete semiconductor chips with thinner aluminum pad were studied and analyzed in this paper.First of all,the knowledge of copper material,the wire bonding tool in this study,EFO(electronic flame-off)ball,bonding process and the crater check method by NaOH were introduced respectively.And then the wire bonding process was studied by three stages.It was found that initial force,contact force and bonding force had an inter-impact to each other.When the force parameter of three stages was set from big to small,the damage to silicon interface can be released smoothly.Lastly,the first bonding parameters were optimized and the security QC control limit was set.The wire pull limits were 8-11 g,and the ball shear test limits were 40-60 g.The bonding power was suggested to be set as small as possible while the wire pull can meet the QC limits.And it was also found that the bonding force should be set 20 g smaller than contact force,contact force should be set 40 g smaller than initial force.Initial force parameter with less than 100 g was recommended in thin Al pad of die.